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ELEMENTS OF
STEAM AND GAS POWER ENGINEERING

VMeQraw-M Bock (h. Jne

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ELEMENTS OF

STEAM AND GAS POWEE
ENGINEERING

BY
ANDREY A. POTTER

DEAN OF ENGINEERING, PURDUE UNIVERSITY, FORMERLY DEAN OF ENGINEERING,

KANSAS STATE AGRICULTURAL COLLEGE. AUTHOR OF "FARM MOTORS",

ENGINEERING THERMODYNAMICS, ETC.

AND

JAMES P. CALDERWOOD

PROFESSOR OF MECHANICAL ENGINEERING IN THE KANSAS STATE AGRICULTURAL
COLLEGE. AUTHOR OF ENGINEERING THERMODYNAMICS, ETC.

First Edition
Fourth Impression

McGRAW-HILL BOOK COMPANY, Inc.
NEW YORK: 370 SEVENTH AVENUE

LONDON : 6 & 8 BOUVERIE ST., E. C. 4

BSD. OBuARr

XHE MAPLE PRESS YORK: PA

PREFACE

In the preparation of this treatise the authors have attempted
to present a clear and concrete statement of the principles under-
lying the construction and operation of steam and gas power
equipment.

The first chapter is devoted to a general survey of the field
of power engineering and brings out the factors essential for the
production of power, the principles governing the action of
various mechanical motors, and a comparison of their
performance.

The main portion of the book is divided into three parts.
The first part takes up the subject of steam power and includes
fuels, combustion, theory of steam generation, boilers, boiler
auxiliaries, boiler accessories, steam engines, steam turbines,
auxiliaries for steam engines and turbines, and the testing of
steam power equipment. The second part is devoted to gas
power and includes a study of the internal combustion engine,
fuels for internal combustion engines, gas producers and the
various auxiliaries found in connection with internal combustion
engine power plants. The last portion of the book treats of the
application of steam and gas power to locomotives, automobiles,
trucks and tractors.

The method followed in each chapter was to give: first,
the fundamental principles underlying the particular phase of
equipment under consideration; second, the structural details;
third, auxiliary parts; fourth, operation and management of the
equipment considered.

This book has been prepared primarily as a textbook for
students in engineering schools and colleges in order to familiarize
them with power plant equipment before they take up the more
abstract study of thermodynamics and design. The subject
matter of this treatise is so prepared that it should prove of
considerable value to those who are responsible for the operation
of steam or internal combustion engine power plants. Illustrative

***->

vi PREFACE

problems will be found at the close of each chapter. These
problems are intended mainly as a guide in encouraging outside
reference reading.

In the preparation of this text the authors are particularly
indebted to H. W. Davis and A. J. Mack of the Kansas State
Agricultural College for their valuable assistance.

The authors are also grateful to E. M. Shealy, J. A. Moyer,
A. J. Wood, C. F. Gebhardt, L. H. Morrison, R. H. Fernald,
G. A. Orrok, and A. M. Greene for their permission to use certain
illustrations from publications of which they are authors. The
various manufacturers of power machinery have also been most
liberal in giving the authors permission to use cuts.

Andrey A. Potter.
James P. Calderwood.
Manhattan, Kansas,
January, 1920.

& *Vtf

CONTENTS

Page
Preface . . . . v

CHAPTER I

Fundamentals of Power Engineering 1

Mechanical Power — Factors Essential for the Production of
Power — Sources of Energy — Principles Governing the Action of
Various Mechanical Motors — Comparison of Various Types of
Motors — Principal Parts of a Steam Power Plant — Condensing
Steam Power Plant — Gas Power Plants — Problems.

CHAPTER II

Steam Power Fuels and Combustion 10

Fuels. The Heating Value of Fuels — The Proximate Analysis
of Fuels — Fuels for Steam Generation.

Combustion. Chemistry of Combustion — Air Required for Com-
bustion— Flue Gas Analysis.
Problems.

CHAPTER III

Steam 21

Theory of Steam Generation — Quality of Steam — Steam Tables —
Determination of the Quality of Steam — Problems.

CHAPTER IV

Boilers 35

Classification of Boilers — Plain Cylindrical Boiler — Horizontal
Return Tubular Boiler — Scotch Marine Boiler — Locomotive Boiler
— Vertical Fire Tube Boiler — Water Tube Boilers — Babcock and
Wilcox Boiler — Heine Boiler — Stirling Boiler — Wickes Boiler
— Parker Down Flow Boiler — Marine Water Tube Boilers —
Materials — Heating Surface — Staying — Settings and Furnaces
— Capacity and Efficiency of Steam Boilers — Firing — Management
of Boilers — Problems.

CHAPTER V

Boiler Auxiliaries 58

Superheaters. Types of Superheaters — Babcock and Wilcox
Superheater — Stirling Superheater — Heine Superheater — Foster
Superheater.

vii

viii CONTENTS

Page

Mechanical Stokers. The Field of Mechanical Stokers — Chain-
grate Stokers — Inclined Grate Stokers — Under-feed Stokers —
Taylor Stoker.

Feed Water Heaters and Economizers. Feed Water Heaters —
Economizers.

Draft Producing Equipment. Chimneys — Artificial Draft.
Feed Pumps and Injectors. Feed Pumps — Injectors — Duty of
Pumps.

Grates for Boiler Furnaces.
Coal and Ash Handlinq Systems.
Problems.

CHAPTER VI

Piping and Boiler Room Accessories 83

Grades and Sizes of Piping — Pipe Fittings — Expansion of Piping —
Pipe Covering — Erecting Pipe — Valves — Blow-off Valves — Safety
Valves — Steam Gages — Water Glass and Gage Cocks — Water
Column — Steam Traps — Fusible Plugs — Problems.

CHAPTER VII

Steam Engines 92

Description of the Steam Engine — Early History of the Steam
Engine — Losses in Steam Engines — Action of the Plain Slide Valve
— Types of Plain Slide Valves — Balanced Valves — The Double
Ported Valve — The Corliss Engine — Poppet Valves — The Uniflow
Steam Engine — Reversing Engines — Condensing and Non-Con-
densing Engines — Multiple Expansion Engines — The Steam Loco-
mobile— Valve Setting — Setting Corliss Valves — Horsepower
— Indicated Horsepower — Indicator Reducing Motions — The
Indicator Card — The Measurement of Power from Indicator
Cards — Valve Setting by Indicator Cards — Brake Horsepower
— Friction Horsepower — Mechanical Efficiency — Steam Engine
Governors — Engine Details — Lubricators — Steam Engine Econ-
omy— Installation and Care of Steam Engines — Problems.

CHAPTER VIII

Steam Turbines 135

Advantages of the Steam Turbine — History of the Steam Turbine
The DeLaval Simple Impulse Steam Turbine — Velocity and Energy
of Steam — Compound Impulse Turbines — The Rateau Turbine —
The Kerr Turbine — The DeLaval Multiple Impulse Turbine —
The Terry Turbine— The Sturtevant Turbine— The Westing-

CONTENTS ix

Page
house Impulse Turbine — The Curtis Steam Turbine — The Reaction
Turbine — The Parsons Turbine — The Impulse-Reaction Turbine —
The Spiro Steam Turbine — Exhaust Steam Turbines — Applications
of the Steam Turbine — Steam Turbine Economy — Installation and
Care of Steam Turbines — Problems.

CHAPTER IX

Engine and Turbine Auxiliaries 164

Condensers. The Principle of the Condenser — The Measurement

of Vacuum — Types of Condensers — Jet Condensers — Barometric

Condensers — Ejector Condensers — Surface Condensers.

Vacuum Pumps. Wet Air Pumps — Edwards Air Pump — Dry Air

Pumps — Circulating Pumps.

Cooling Ponds and Cooling Towers. Reclaiming Cooling Water —

Cooling Ponds — Spray Ponds — Cooling Towers.

Separators. Steam Separators — Exhaust Steam and Oil Separators

— Exhaust Heads.

Problems.

CHAPTER X

Steam Power Plant Testing 182

General Rules — Preparing for the Test — Starting and Stopping
the Test — Weighing the Fuel — Weighing the Feed Water — Draft
Gages — Temperature Measurement — Measuring the Weight of
Steam — Measurement of Power — Measurement of Speed — In-
dicator and Calorimeters — A. S. M. E. Code — Problems.

CHAPTER XI

Internal Combustion Engines 191

History — The Otto Internal Combustion Engine Cycle — The Two-
stroke Cycle Engine — The Diesel Internal Combustion Engine
Cycle — Details of Internal Combustion Engines — Oil Engines —
Losses in Internal Combustion Engines — Installation and Care of
Internal Combustion Engines — Problems.

CHAPTER XII

Internal Combustion Engine Fuels and Gas Producers 211

Fuels. Classification of Fuels — The Heating Value of a Fuel —
Selection of a Fuel — Distillates of Crude Petroleum — Gasoline —
Kerosene — Crude Oil — Alcohol — Benzol — Shale Oil — Fuel Gases —
Blast-furnace Gas — Coke-oven Gas — Natural Gas — Producer Gas.
Gas Producers. Details of Gas Producers — Classification of Gas

x CONTENTS

Page
Producers — Suction Gas Producers — Pressure Gas Producers —
Combination Producers — Rating of Gas Producers — Factors
Influencing Producer Operation.
Problems.

CHAPTER XIII

Auxiliaries for Internal Combustion Engines 228

Carburetors. Principles of Carburetion — Carburetors — Simple Car-
buretors or Mixed Valves — Float Feed Carburetors — Kingston
Carburetor — Marvel Carburetor — Stewart Carburetor — Stromberg
Carburetor — Zenith Carburetor — Holly Carburetor — Kerosene
Carburetors.

Ignition Systems. Electric Ignition Systems — The Make-and-
Break System of Ignition — The Jump Spark System of Ignition —
Comparison of the Two Systems of Electric Ignition — Source of
Current — Electric Batteries — Primary Batteries — Storage Batteries
— The Lead Storage Battery — The Edison or Nickel-Iron Storage
Battery — Ignition Dynamos — Magnetos — Low Tension Magnetos
— Inductor Type of Magneto — High Tension Magnetos — Timer
and Distributor Systems.

Governors. Hit-and-Miss Governing — Quality Governing — Quan-
tity Governing — Combination Systems.
Mufflers.
Problems.

CHAPTER XIV

Gas Power Plant Testing , . . 255

Measurement of Fuel Used — Heat Consumption of the Engine —
Brake Horsepower — Indicated Horsepower — The Measurement
of the Heat Absorbed by the Jacket Water — Duration of Test —
Starting the Test — Gas Producer Testing — A. S. M. E. Code —
Problems.

CIJAPTER XV

Locomotives 260

The Locomotive Compared with the Stationary Steam Power Plant
— The Essential Parts of a Locomotive — Early History of the
Locomotive — Classification of the Locomotive — The Development
of the Locomotive — The Mallet Articulated Compound Locomotive
Superheaters — Locomotive Stokers — Draft Appliances — Injectors
— Air Brakes — Problems.

CONTENTS xi

Page
CHAPTER XVI

Automobiles, Trucks and Tractors 273

Automobiles. Types of Automobiles — Essential Parts of a Gasoline
Automobile— Automobile Motors — Cooling of Automobile Motors-
Lubrication — Automobile Valves — Clutches — Transmissions — Dif-
ferentials for Automobiles — Universal Joint — Front and Rear- Axles
— Steering and Control Systems — Brakes — Wheels and Tires — Car-
buretors— Ignition — Automobile Starting Systems — Automobile
Lighting — Management of Automobiles.

Trucks. Power Plants for Trucks — Power Transmission Systems
for Trucks.

Tractors. Essential Parts of a Tractor — Steam Tractors — Gas
Tractors — Rating of Tractors — Care of Trucks and Tractors.
Problems.

Index 299

ELEMENTS OF STEAM

AND

GAS POWER ENGINEERING

CHAPTER I
FUNDAMENTALS OF POWER ENGINEERING

Mechanical Power. — The substitution of mechanical power for
animal labor marks a most important epoch in the progress of
civilization. The increase in the amount of mechanical power
used for manufacturing, for transportation, and for other pur-
poses has been enormous during the past forty years and particu-
larly so in the United States of America. The greatest factors
which contributed to the increased use of power are the develop-
ment of electrical machinery and efficient electrical transmission
systems, the perfection of the internal combustion engine and
steam turbine, the growth of the manufacturing industries, and
the improvements in transportation equipment and systems.

Factors Essential for the Production of Power. — Two require-
ments are essential for the production of power: first, a source
from which energy may be derived ; and second, a motor which is
capable of transforming this energy into work. Without energy
all attempts to produce power would be futile; without a motor
energy cannot be utilized, even when available, in producing
power.

A motor is an apparatus capable of transforming energy into
mechanical work. Any apparatus which transforms energy
from one form into another, but not into work, is not a motor.

2 STEAM AND GAS POWER ENGINEERING

A Motor Must Do Work. By work is meant the production
of motion against some external force. The mechanical motors
available for the production of power are heat engines, including
steam, gas, oil, hot-air, and solar engines; pressure engines, such
as water wheels and water motors; windmills; electric motors.

Sources of Energy. — The principal source of all energy is the
sun. It causes the growth of plants which furnish food for man
and animals. The great coal deposits are only the result of the
storing up of the sun's rays in plants in bygone days. These
rays are also responsible for the raising of water from sea level to
mountain top, thus giving it energy which can be utilized to turn
water wheels and do useful work.

On the other hand, while the sun's rays are the fundamental
source of all energy, they can be utilized directly by man only to
a very limited extent. Heat engines have been built which
transform the heat derived directly from the sun into mechanical
energy; but, because of their bulk when compared with the energy
transformed and because of the irregularities in the sun's rays
caused by clouds and the movement of the earth, this type
of motor has never proved practicable. As a result, secondary
sources of energy must be utilized. These secondary sources
are: the wind; waterfalls; carbon in different forms, such as coal,
petroleum, or gas; and chemicals such as are used in electric
batteries.

Principles Governing the Action of Various Mechanical
Motors. — All mechanical motors do work by virtue of motion
given to a piston, or to blades on a wheel by some substance such
as water, steam, gas, or air; or to a rotor by electricity. The
first requirement in any of these cases is that the above-men-
tioned substance, often called the working substance, be under
considerable pressure.

This pressure in the case of the water motor or waterwheel is
obtained by collecting water in dams and tanks, or by utilizing
the kinetic energy of natural waterfalls. The total power
available in water when in motion depends on the weight of
water discharged in a given time and on the head or distance
through which the water is allowed to fall. The head of water
can be utilized by its weight or pressure acting directly either on
a piston, or on blades or paddles on wheels.

FUNDAMENTALS OF POWER ENGINEERING 3

Considering next the various forms of heat engines, we find
work accomplished by steam or gas under pressure, the pressure
being obtained by utilizing the heat of some fuel or of the rays
of the sun.

A motor utilizing the heat of the sun is called a solar motor or a
solar engine. The action of this type of motor depends on the
vaporization of water into steam by means of the rays of the sun,
which are concentrated and intensified by means of reflecting
surfaces. The steam thus generated is used in some form of heat
motor.

In the case of the steam power plant (Fig. 1, page 6) a fuel,
like coal, oil, or gas, is burned in a furnace and its heat of com-
bustion is utilized in changing water into steam at high pressure
in a special vessel called a boiler. This high-pressure steam is
then conveyed by pipes to the engine cylinder where its energy
is expended in pushing a piston as in the case of the reciprocating
engine. The sliding motion of the piston may be changed into
rotary motion at the shaft by the interposition of a connecting
rod and crank. Another method is to allow the high-pressure
steam to escape through a nozzle, strike blades on a wheel and
produce rotary motion direct, as in the case of the steam turbine
(Fig. 109, page 135).

In another type of heat engine, called a hot-air engine, air is
heated in the engine cylinder by a fuel which is burned outside
of the cylinder. The air by its expansion drives a piston and
does work.

In the case of gas and oil engines (Fig. 163, page 194), the fuel
which must be in a gaseous form as it enters the engine cylinder,
is mixed with air in the proper proportions to form an explosive
mixture. It is then compressed and ignited within the cylinder
of the engine, the high pressure produced by the explosion push-
ing on a piston and doing work. These engines belong to a class f
called internal-combustion engines, and differ from the steam and
hot-air engines, which are sometimes called external-combustion
engines, in that the fuel is burned inside the engine cylinder, in-
stead of in an auxiliary apparatus.

The windmill derives its high pressure for doing work from the
moving atmosphere.

The electric motor converts electrical energy at high pressure

4 STEAM AND GAS POWER ENGINEERING

into work; this electrical pressure or voltage is produced in an
apparatus called an electrical dynamo, or a generator of electricity.

Comparison of Various Types of Motors. — The solar motor, as
previously stated, is but little used on account of its high first
cost and great bulk in relation to the small power developed.

In localities where the wind is abundant and little power is
needed, the windmill is a desirable and cheap source of power.
The greatest application of windmills is for the pumping of
water for residences and farms, and for such other work as does
not suffer from suspension during calm weather. Electric storage
and lighting on a small scale from the power of a windmill has
been tried in several places with fair success, but probably will
not be adopted to any great extent on account of the high first
cost and the small practical capacity of such an installation.

The water motor or water turbine is very economical if a
plentiful supply of water can be had at a fairly high head, but
its reliability is affected by drought, floods, and ice in the water
supply. For this reason many of the hydraulic power stations
must resort to the use of steam or gas power during certain
seasons of the year.

The hot-air engine, while not economical in fuel consumption,
is used to a limited extent for pumping water in places where the
cost of fuel is not an important item and where safety and sim-
plicity of mechanism are essential. The hot-air engine, on ac-
count of its high cost, bulk, and poor fuel economy, has been
largely superseded by the oil engine, which uses gasoline or the
heavier oils.

The internal-combustion engine (Chapter XI), whether using
gas or oil, is well adapted for small and medium-sized powers.
It finds its greatest application in the automobile and in other
power vehicles (Chapter XVI) ; also for uses on farms either as
stationary engines or as oil traction engines.

For the generation of electricity, especially in large units, the
steam engine (Chapter VII) and the steam turbine (Chapter VIII)
have been found to be the most suitable types of motors, because
of their lower first cost, when compared with other types of
motors, and because of their greater reliability. By far the great-
est part of commercial power is developed by steam motors.
The reason for this fact is that the conversion of power from one

FUNDAMENTALS OF POWER ENGINEERING 5

form into another is always accompanied by losses; thus power
developed from a cheap source is not necessarily the most eco-
nomical from a commercial point of view. An example of this is
the hydro-electric plant, where the cost of power would be small
if no consideration had to be taken of the greater first cost of the
installation and the cost of the long transmission lines. As
another illustration, the oil engine is conceded to have the highest
efficiency as a motor for the transforming of heat energy into
work, but commercially its application has been limited to special
uses or to those localities in which the cost of oil is low and the
supply is large. When all factors are considered, it is usually
found that the steam power plant is the cheapest producer of
power in large quantities.

About three-fourths of the total power used for manufacturing
in this country is developed by steam prime movers; that is by
steam engines and steam turbines. In electric generating sta-
tions over 70 per cent, of the power is developed by steam prime
movers and but slightly more than 1 per cent, by internal com-
bustion engines. The power developed by gas and oil engines
in connection with the manufacturing industries is less than 5 per
cent.

Principal Parts of a Steam Power Plant. — The principal parts
of a simple steam power plant are illustrated in Fig. 1, and include
the following:

1. A furnace, in which the fuel is burned. This consists of a
chamber arranged with a grate (1), if coal or any other solid fuel
is used, and with burners when the fuel is in the liquid or gaseous
state. The furnace is connected through a flue or breeching (2)
to a chimney. The function of a chimney is to produce sufficient
draft, so that the fuel will have the proper amount of air for
combustion; it also serves to carry off the obnoxious gases after
the combustion process is completed. The flue leading to the
chimney is provided with a damper (3), so that the intensity of
the draft can be regulated.

2. A boiler (4), which is a closed metallic vessel filled to about
two-thirds of its volume with water. The heat developed by the
burning of the fuel in the furnace is utilized in converting the
water contained in the boiler into steam. The boiler (4) is
arranged with a water column (5) to show the water level, with

STEAM AND GAS POWER ENGINEERING

a safety valve (6) to prevent the pressure from rising too high,
and with a gage (7) to indicate the steam pressure.

3. The function of a setting, which is the term usually used to
designate the brick work which surrounds the boiler, is to provide
correct spaces for the furnace, combustion chamber and ash-pit,
to prevent air from entering the furnace above the fuel bed, and
to decrease the heat of radiation to a minimum. In some power
plants the setting is also used to support the boiler shell, but this
is poor practice.

Fig. 1. — Elementary non-condensing power plant.

4. The feed pump (8) supplies the boiler with water through
the feed pipe (9).

5. The steam lines (10) and (11) convey steam from the boiler
to the engine and to the steam end of the pump respectively.

6. In the engine the energy of the steam is expended in doing
work. The steam enters the engine cylinder (12) through the
valve (13) and pushes on the piston (14). The sliding motion
of the piston, which is transmitted to the piston rod (15), is
changed into rotary motion at the shaft (16) by means of a con-
necting rod (17) and crank (18).

FUNDAMENTALS OF POWER ENGINEERING

STEAM AND GAS POWER ENGINEERING

7. The exhaust pipe (19) conveys the used steam to the atmos-
phere, or to some use where its heat is abstracted, converting
the steam back into water.

Condensing Steam Power Plant. — In Fig. 2 is illustrated a
condensing steam power plant with water tube boilers. The
various parts are numbered to correspond with similar parts in
the simple power plant of Fig. 1.

Fig. 3. — Modern steam power plant.

In Fig. 3 is illustrated a modern steam turbine plant equipped
with coal and ash handling machinery, mechanical stokers, and
other labor saving devices.

Gas Power Plants. — The equipment of a gas power plant de-
, pends upon the fuel used. The simplest type of gas power plant
is the gasoline engine (Fig. 163), which consists of a cylinder and

FUNDAMENTALS OF POWER ENGINEERING 9

piston, a carburetor for preparing the explosive mixture, valves
for admitting the mixture to the cylinder and for expelling the
burnt gases to the atmosphere, a device for igniting the mixture
at the proper time, a mechanism for changing the reciprocating
motion of the piston into rotary motion, a governor to keep the
speed constant at variable loads, a lubrication system for the
cylinder and bearings, an arrangement for cooling the cylinder
walls, a flywheel to carry the engine through the idle strokes,
and bearings and a frame to support the various parts.

Details concerning various types of gas power plants will be
given in Chapter XI.

Problems

1. Make a thorough study of some non-condensing steam power plant in
your vicinity and hand in a report concerning the important details. State
in which respects the power plant you have examined differs from that illus-
trated in Fig. 1.

2. Make a sketch showing how the piping in a non-condensing power
plant would be modified if the exhaust steam is used for heating.

3. Make a study of some internal combustion engine power plant and
hand in a report concerning fuel used and fundamental details of the engine.

CHAPTER II
STEAM POWER FUELS AND COMBUSTION

Fuels

The fuel in the case of the steam power plant is burned under
the boiler, and its heat is utilized in changing water into steam.

Fuels may be used in their natural state, or may be prepared
or manufactured in various ways. The chief natural fuels are
coal, wood, petroleum oil, and natural gas. The chief prepared
fuels are coke made from the distillation of coal, artificial gas
made from solid or liquid fuels, and the various petroleum distil-
lates. Another prepared fuel is briqueted coal which is made by
pressing finely ground coal into brick form, the particles being
held together by some cementing material. There are a great
many other materials which could be used for fuel, such as acety-
lene, alcohol, and benzol, that have valuable fuel properties, but
their high cost makes their use prohibitive. Then again there is
another class of fuel which is derived as a by-product in various
industries. To this class belongs gas discharged from blast
furnaces which has considerable value as a fuel.

The Heating Value of Fuels. — By the heating value of a fuel,
often expressed by the terms, heat of combustion, calorific value,
and heat content, is meant the amount of heat liberated by the
perfect combustion of one unit weight of a solid or liquid fuel,
or of a unit volume of a gaseous fuel. The value of the fuel for
power purposes is dependent upon its heat content in a unit
weight. Thus of two grades of coal, the one containing the
greater heating value is the most desirable commercially, other
things being equal.

The heating value of the fuel is measured in heat units. A
heat unit is the amount of heat required to raise the temperature
of one pound of water one degree. The unit used in English

STEAM POWER FUELS AND COMBUSTION 11

speaking countries is the British thermal unit (B.t.u). TheB.t.u.
is denned as the amount of heat required to raise the temperature
of one pound of water from 62 to 63 degrees Fahrenheit. An-
other definition of a B.t.u. is Jf80 of the heat required to raise
the temperature of one pound of water from the freezing point
to the boiling point on the Fahrenheit scale.

This calorific value or the heating value of a fuel may be
determined by means of a chemical analysis, but a more satisfac-
tory determination can be made by an instrument, called a coal
calorimeter.

Several different types of coal calorimeters are available, but
those of the bomb type, similar to the one illustrated in Fig. 4,
are the most accurate and satisfactory for determining the

Fig. 4. — Bomb calorimeter.

heating value of solid and heavy liquid fuels. This type of
instrument consists of a steel vessel or bomb, lined with porcelain,
platinum, or gold to prevent corrosion, and into which a weighed
sample of the fuel is introduced. The bomb, after it has been
charged with fuel, is filled with oxygen from the cylinder 0,
to which the bomb is connected through the union U. The
quantity of oxygen admitted to the bomb is regulated by means
of the valve W and the pressure gage M . The bomb is then
placed in the calorimeter vessel A , which contains a known weight

12 STEAM AND GAS POWER ENGINEERING

of water. The water is agitated by the stirring mechanism
shown and the thermometer T indicates its rise in temperature
when the fuel within the bomb is burned. The calorimeter
vessel A is fitted with a water jacket which reduces the effect
of external changes of temperature and causes a more uniform
temperature of the thermometer T. The fuel charge is ignited
electrically and burns in the presence of oxygen. The heating
value of the fuel is calculated from the observed temperature rise
of the water as indicated by thermometer T, since the heat
gained by the water must equal the heat given up by the fuel,
after making allowances for radiation and other similar factors
which may produce a gain or loss of heat.

The Proximate Analysis of Fuels. — While the heating value of
a fuel is important in estimating its commercial value, other
properties must be considered as well. Two different coals, for
instance, may have the same heating value but the properties
of one, not disclosed by the heating value, may cause it to be
more or less desirable than the other coal. The proximate
analysis of a fuel has been devised to assist in this. The
proximate analysis determines the amount of moisture, volatile
matter, fixed carbon, ash and sulphur.

Moisture requires heat for its evaporation, and is direct loss.
Ash, when present in large amounts, will form clinkers, and is
also an item of expense in its disposal. Sulphur is usually con-
sidered a detrimental constituent, especially if in amounts greater
than 2 per cent. Coals containing large quantities of sulphur
are usually avoided.

The volatile matter and the fixed carbon are the heat producing
constituents of the coal. The volatile matter represents that
part which distils off at a comparatively low temperature, and
may be considered the gaseous or flaming constituent. The
amount of volatile matter gives some conception of the smoke
producing qualities of the fuel. If smokeless combustion must
be secured in any particular plant, and no special furnaces have
been installed which will insure the proper combustion of volatile
gases, a coal with a large content of volatile matter should not
be selected. The fixed carbon is just the reverse of the volatile
matter; it being that part of the coal which burns without flame
and consequently gives no trouble from smoke.

STEAM POWER FUELS AND COMBUSTION 13

Fuels for Steam Generation. — The fuels most commonly used
for steam generation are coal, wood, petroleum oils, and natural
gas.

Wood is but little used for steam generation except in remote
places, where timber is plentiful, or in special cases where saw-
dust, shavings, and pieces of wood are by-products of manufac-
turing operations. Wood burns rapidly and with a bright flame,
but does not evolve much heat. When first cut, wood contains
30 to 50 per cent, of moisture, which can be reduced by drying
to about 15 per cent. One pound of dry wood is equal in heat-
producing value to about % lb. of soft coal. It is important
that wood be dry, as each 10 per cent, of moisture reduces its
heat-producing value as a fuel by about 12 per cent. The chem-
ical compositions and the calorific values of some of the more
common woods are shown in Table 1.

Table 1. — Analysis and Calorific Value of Dry Wood

Kind of wood

Carbon

Hydrogen

Nitrogen

Oxygen

Ash

B.t.u.
per pound

Oak

50.16
49.18
48.99
49.06
48.88
50.36
50.31

6.02
6.27
6.20
6.11
6 06
5.92
6.20

0.09
0.07
0.06
0.09
0.10
0.05
0.04

43.36
43.91
44.25
44.17
44.67
43.39
43.08

0.37
0.57
0.50
0.57
0.29
0.28
0.37

8,316
8,480
8,510

Ash

Elm

Beech

8,591
8,586
9,063
9,153

Birch

Fir

Pine

Coal is more extensively used as a fuel for steam generation
than any other substance. It is a substance which results from
collections of vegetable matter, which has been gradually changed
in physical and chemical composition until it finally became coal.

In the first stages of the transformation the material is classed
as peat. In its next stage it is known as lignite or brown coal.
Following this in the proper order of transformation are soft or
bituminous coal, semi-bituminous, semi-anthracite, and finally
anthracite or hard coal.

Table 2 gives the proximate analyses and the calorific values
of American coals.

STEAM AND GAS POWER ENGINEERING

Table 2. — Composition and Calorific Value of American Coals
(U. S. Bureau of Mines)

State

Classification

Proximate analysis

Mois-
ture

Vola-
tile
matter

Fixed
carbon

Ash

Sul-
phur

B.t.u.
per lb.,
dry coal

Pennsylvania..
Pennsylvania..
Pennsylvania..
Pennsylvania..
West Virginia.

Colorado

Illinois

Kansas

Kentucky

Missouri

Ohio

Oklahoma. . . .
Pennsylvania..
West Virginia.

Colorado

North Dakota
Wyoming

Anthracite

Semi-anthracite.
Semi-bituminous
Semi-bituminous

Bituminous

Lignites

2.19

3.43

5.48

2.72

3.17

10.27

7.12

11.10

4.83

5.87

5.15

4.83

3.48

3.36

20.71

32.65

23.46

5.67
6.79
7.53
16.70
18.46
38.25
34.55
35.51
33.71
30.98
37.34
35.76
35.15
22.50
31.82
30.57
35.64

86.24
78.25
81.00
75.38
70.86
44.99
50.68
40.69
57.73
51.67
49.00
55.55
55.45
68.86
43.98
28.49
35.73

5.90

11.53

11.47

5.20

7.51

6.49

7.65

12.70

3.73

11.48

8.51

3.86

5.92

5.28

3.45

8.29

5.17

0.57
0.46

0.55
1.07
0.42
2.23
3.99
0.82
5.00
2.94
1.34
1.18
0.52
0.45
1.33
0.49

13,828
12,782
13,547
14,521
13,995
11,416
12,481
11,065
13,842
12,339
12,733
13,829
13,700
14,369
9,941
7,357
9,050

The weight of coal per cubic foot will vary from 43 to 58
pounds. An anthracite coal will have a greater weight than a
bituminous coal; the higher the amount of fixed carbon in the
coal, the greater is its weight.

Anthracite, commonly known as hard coal, is the highest grade
of coal. It consists mainly of fixed carbon having little, and in
some cases no, volatile matter. Some varieties approach graph-
ite in their characteristics, and are burned with difficulty unless
mixed with other coals. This coal is slow to ignite, burns with a
short flame, and gives an intense fire free from smoke. As it is
available for steaming purposes only in certain limited sections,
its use is not common.

Semi-anthracite coal is softer and lighter than anthracite. It
contains less carbon than anthracite coal, and its volatile matter
ranges from 7 to 12 per cent. It ignites more readily than
anthracite and makes an intense, free-burning fire.

Semi-bituminous coal has all the physical characteristics of
bituminous coal, but it differs from it in that the volatile matter
content is not so high. Semi-bituminous coal contains from 12

STEAM POWER FUELS AND COMBUSTION 15

to 25 per cent, volatile matter, and when compared with semi-
anthracite coal its fixed carbon is less.

Bituminous coal is a classification intended to include coals
which contain 20 per cent, or more volatile matter and less than
60 per cent, of fixed carbon. One objection to the use of bitu-
minous coal as a fuel is its smoking quality. This may be an
undesirable feature, especially if its use is in a city where smoke
ordinances are enforced and when special smokeless furnaces
have not been installed. Another feature which may be con-
sidered undesirable is the tendency for highly volatile coals to
ignite spontaneously.

Bituminous coal constitutes over 85 per cent, of the fuel used
in manufacturing, when including the manufacture of coke.
The term bituminous coal is broad in its interpretation, and
includes a great variety of coals which have many different quali-
ties. For this reason many of the coals of this classification are
given special names depending upon some marked physical
characteristic they possess. Dry or free burning bituminous
coal is one of the best of the bituminous varieties for steaming
purposes. As compared with other bituminous coals, it is low in
volatile matter and burns with a short bluish flame. Bituminous
caking coals is the term applied to those varieties that swell up,
become pasty and fuse together in burning. They contain a
greater amount of volatile matter than the dry bituminous coals
and for that reason burn with a larger flame and have a greater
tendency to smoke. Long flaming bituminous coals are those
containing the greatest amounts of volatile matter. They possess
a strong tendency to produce smoke. Cannel coal is a variety
rich in volatile matter. It is used principally in the manufac-
ture of artificial gas. It differs in appearance from the other
varieties in that it has a dull resinous luster. Its volatile content
varies from 45 to 60 per cent. It is seldom used as a steaming
coal, though it is sometimes mixed with other coals containing
less volatile matter.

Lignite may be classified as coal in the process of formation.
This coal contains a very large proportion of volatile matter
and less than 50 per cent, fixed carbon. However, it has a good
heating value and burns freely, but owing to the high percentage
of volatile matter it will not stand storage, but crumbles badly

STEAM AND GAS POWER ENGINEERING

soon after exposure to air. Its use is restricted to those localities
in which it is found.

Other solid fuels used to some extent for steam generation are :
Peat, which is an intermediate between wood and coal and is
found in bogs; sawdust; oak bark after it has been used in the
process of tanning; bagasse, or the refuse of cane sugar; and
cotton stalks. Coke is also used to some extent, the advantage of
this fuel as compared with coal being that coke will not ignite
spontaneously, will not deteriorate or decompose when exposed
to the atmosphere, and produces no smoke when burned. Coke
is manufactured by burning coal in a limited air supply, the
volatile hydrocarbons being driven off during the process.

Petroleum fuels, either in the form of crude petroleum or as the
refuse left from its distillation, are used for making steam to a
considerable extent in certain parts where the relative cost
of oil is less than that of coal. It has been estimated that
petroleum oils at 2 c. per gallon are equally economical for steam
making with coal at $3 per ton. The advantages of oil, as com-
pared with solid fuels, are ease of handling, cleanliness, and
absence of smoke after combustion. Table 3 gives the analysis
and heating value of several American petroleum oils.

Table 3. — Analysis and Calorific Value of Oils (C. E. Lucke)

Classification

Density at
60°F.

Ultimate analysis

Heating value
B.t.u. per lb.

gr-

°B6.

o2+

High

Low

California fuel

0.966
0.926
0.957
0.924
0.914
0.866
0.841
0.829

14.93
21.25
16.24
21.56
23.18
31.67
36.47
38.89

81.52
83.26
86.30
84.60
86.10
85.40
84.30
85.00

11.61
12.41
16.70
10.90
13.90
13.07
14.10
13.80

6.92
3.83

2.97

1.6
0.6

0.55
0.50
0.80
1.63
0.06

0.6

18,926
19,654
21,723
18,977
20,949
20,345
20,809
20,752

17,903

Texas, Beaumont fuel

California crude

18,570
21,254

Texas, Beaumont crude

Pennsylvania crude

18,025
19,735

19,203

West Virginia crude

Ohio crude

19,578
19,547

Natural gas is used for steam generation only in natural gas
regions, where its cost is very low. If the cost of natural gas is
greater than 10 cents per 1,000 cu. ft., it cannot compete with
coal at $3 a ton. Illuminating gas and other artificial gas is
too expensive for steam generation and cannot compete with

STEAM POWER FUELS AND COMBUSTION 17

other fuels. The heating values of various gaseous fuels will be
found in Table 4.

Table 4. — Heating Value of Gaseous Fuels

Character of Gas B.t.u. per cu. ft.

Coke-oven Gas 600

Water Gas 275

Blast Furnace Gas 100

Natural Gas 950

Producer Gas 120

Fuels suitable for internal combustion engines are treated in
Chapter XII.

Combustion. — Combustion is a chemical combination of the
heat-producing constituents of a fuel with oxygen, accompanied
by the evolution of heat.

Carbon, hydrogen, and sulphur are the main combustible con-
stituents of all fuels. Of these, the sulphur is of minor impor-
tance in contributing to the heating value, because it is present
in small quantities in fuels suitable for steam power plants.
Carbon is present either in a free, uncombined state or in com-
bination with hydrogen as a hydrocarbon.

Oxygen, the supporter of combustion, is one of the most com-
mon substances found in nature. The largest supply of oxygen
is found in the atmosphere, and it is from this source that the
supply required for the combustion of fuel is derived. Air is
chiefly a mixture of oxygen and nitrogen, although small amounts
of other gases are usually present.

Air contains 0.23 parts by weight of oxygen and 0.77 parts by
weight of nitrogen. Only the oxygen is used in the combustion
of the fuel; nitrogen is an inert gas and has no chemical effect upon
the combustion of the fuel.

Chemistry of Combustion. — In the process of combustion, the
heat producing elements of the fuel, which are carbon, hydrogen,
and sulphur, unite with oxygen from the air.

If the combustion is perfect, the combustibles unite with the
greatest amount of oxygen. Thus in the case of carbon, if the
combustion is perfect, every atom of carbon unites with two
atoms of oxygen forming carbon dioxide (C + 02 = C02), and
liberates 14,600 B.t.u. per pound.

18 STEAM AND GAS POWER ENGINEERING

If there is a lack of oxygen, combustion is imperfect, every
atom of carbon unites only with one atom of oxygen forming
carbon monoxide (C + O = CO) and liberating only 4,400 B.t.u.
for each pound of carbon burned.

Hydrogen, when burned, enters into combination with oxygen,
as indicated by the following chemical reaction, forming water
(H20):

H2 + 0 = H20

The sulphur unites with oxygen to form sulphur dioxide, as
indicated by the following reaction:

S + 02 = S02

The importance of proper air supply in the burning of a fuel
is quite evident from the above. Each pound of carbon when
completely burned is capable of liberating 14,600 B.t.u. If car-
bon is burned to carbon monoxide, only 4,400 B.t.u. will be liber-
ated, producing a loss of 10,200 B.t.u., which is about 70 per cent,
of the original heating value of the carbon. While it would be
an extremely inefficient furnace that would produce much carbon
monoxide, any furnace, unless properly operated, produces more
or less incomplete combustion, with the consequent lower effi-
ciency in the utilization of the fuel.

Air Required for Combustion. — For the complete combustion
of one pound of carbon 2.66 pounds of oxygen, or 11.5 pounds of
air will be theoretically required. Complete combustion will not
be obtained in a boiler furnace if only this theoretical amount of
air is supplied. An excess of air varying from 50 to 100 per
cent, will be required, depending upon the draft and upon the
fuel used. With natural draft, a greater excess of air is
required than with mechanical draft.

Too much air will produce a great loss of heat by diluting the
gases arising from the furnace. Air should be added to the
furnace so that each atom of carbon has sufficient opportunity to
unite with as much air as possible. When this is accomplished no
further excess air is needed. Ordinarily, bituminous coal re-
quires about 20 pounds of air per pound of fuel, or about 250
cubic feet of air per pound of fuel.

Flue Gas Analysis. — The analysis of the gases leaving the
boiler is made to ascertain whether the fuel is being burned

STEAM POWER FUELS AND COMBUSTION 19

economically. If there is an excess of air, too much oxygen will
be present in the flue gases; if there is a deficiency there will be
carbon monoxide present.

Many instruments have been devised to facilitate this analysis.
The fundamental principles upon which they operate are much
the same. A simple device, called an Orsat apparatus and shown

From Flue

Fia. 5. — Orsat apparatus.

in Fig. 5, is commonly used. It consists of three pipettes, A,
B, and C, filled respectively with caustic potash, a mixture cf
caustic potash and pyrogallic acid, and cuprous chloride. A
measuring burette, M, and a displacement bottle, W, is also
provided. The sample of the flue gas to be analyzed is drawn
into the measuring burette. It is then passed into the pipette
A containing the caustic potash where the carbon dioxide is

20 STEAM AND GAS POWER ENGINEERING

absorbed. The gas is then drawn back into the measuring
burette and the shrinkage in volume represents the amount of
carbon dioxide present. The remaining gas is similarly treated
in pipette B where the oxygen is absorbed, and is finally passed to
pipette C where the carbon monoxide is removed.

Perfect combustion is indicated by a flue gas analysis, which
shows about 1 per cent, of carbon dioxide for every 4 per cent,
of nitrogen. Low carbon dioxide may be due to excessive air,
air holes in the fuel bed, or to the infiltration of air through cracks
in the setting. Dirty heating surfaces and the presence of soot
will be indicated by a low carbon dioxide in the flue gases. Too
much oxygen in the flue gases shows excess of air. A good flue
gas analysis will show 4 to 8 per cent, oxygen, 10 to 13 per cent,
carbon dioxide, and no carbon monoxide.

Problems

1. Coal costs $3.00 a ton (2,000 lbs.). If the coal in question has a heat-
ing value of 12,000 B.t.u. per lb , what is the cost in cents of 1,000 B.t.u.?

2. Natural gas costs 15 c. per 1,000 cubic feet. If its heating value is 950
B.t.u. per cu. ft., what is the cost of 1,000 B.t.u.?

3. Fuel oil whose heating value is 18,500 B.t.u. per pound sells at 5 c.
per gallon. Coal with a heating value of 13,000 B.t.u. per pound may be
purchased at a price of $4.00 per ton. Which would be the cheaper fuel if
the estimate is based upon the cost of an equal number of heat units?

4. Compile a table showing composition and heating value of the fuels
most commonly used in your locality.

5. Prove that 2% pounds of oxygen will be required to burn 1 pound
of carbon into carbon dioxide.

6. Prove that 11^ pounds of air will be required to supply 2% pounds
of oxygen.

CHAPTER III
STEAM

Theory of Steam Generation. — If heat is added to ice, the
effect will be to raise its temperature until the thermometer regis-
ters 32°F. When this point is reached a further addition of
heat does not produce an increase in temperature until all the ice
is changed into water, or in other words, the ice melts. It has
been found experimentally that 144 B.t.u. are required to change
1 pound of ice into water. This quantity is called the latent
heat of liquefaction of ice.

After the given quantity of ice, which for simplicity may be
taken as 1 pound, has all been turned into water, it will be found
that if more heat is added the temperature of the water will again
increase, though not as rapidly as did that of the ice. While the
addition of each British thermal unit increases the temperature
of ice 2°F., in the case of water an increase of only about 1° will
be noticed for each British thermal unit of heat added. This
difference is due to the fact that the specific heat, or the resistance
offered by ice to a change in temperature is only one-half that
offered by water. That is, the specific heat of ice is 0.5.

If the water is heated in a vessel open to the atmosphere, its
temperature will continue to rise until it reaches a temperature of
about 212°F., the boiling point of water, when further addition of
heat will not produce any temperature changes, but steam will
issue from the vessel. It has been found that about 970 B.t.u.
are required to change 1 pound of water at atmospheric pressure
and at 212°F. into steam. The quantity of heat so supplied
which changes the physical state of water from the liquid state to
steam is called the latent heat of vaporization.

If the above operations are performed in a closed vessel,
such as an ordinary steam boiler, water will boil at a higher tem-
perature than 212°F., since the steam driven off cannot escape

22 STEAM AND GAS POWER ENGINEERING

and is compressed, raising the pressure and consequently the
temperature.

The fact that the boiling point of water depends on the pressure
is well known. Thus in a locality where the altitude is 6,000 ft.
above sea level and the barometric pressure is 12.6 pounds per
square inch the boiling point of water is about 204°F. as compared
with 212°F. at sea level where the barometric pressure is 14.7
pounds per square inch.

Assuming that the pressure is increased to 60 pounds per
square inch by the gage, it will be found that the boiling point of
water is 307.3°F. At 100 pounds per square inch water will
boil at 337. 9°F. and at 150 pounds the temperature will read
365.9°F. before steam will be formed.

Quality of Steam. — Steam formed in contact with water is
known as saturated steam, which may be wet or dry.

In the first case steam carries with it a certain amount of water
which has not been evaporated. The percentage of this water
determines the condition or the quality of the steam; that is, if
the steam contains 3 per cent, by weight of moisture, the steam
is spoken of as being 97 per cent. dry. A stationary steam
boiler, properly erected and operated and of suitable size, should
generate steam that is 98 per cent. dry. If there is more than 3
per cent, moisture, there is every reason to believe that the boiler
is improperly installed, inefficiently operated, has too small a
space for the disengagement of the steam from the water, or is
too small for the work to be done.

In the second condition, that of being dry steam, the vapor
carries with it no water that has not been evaporated ; that is, it
is dry. Any loss of heat, however small, not accompanied by a
corresponding reduction in pressure, will cause condensation,
and wet steam will be the result. Steam, whether wet or dry,
has a definite temperature corresponding to its pressure.

An increase in temperature not accompanied by an increase in
pressure will cause the steam to acquire a condition that will
permit a loss of heat at constant pressure without condensation
necessarily following. This condition is called superheat.
The advantage of superheated steam lies in the fact that its tem-
perature may be reduced by the amount of superheat without
causing condensation. This makes it possible to transmit the

STEAM

steam through mains and still have it dry and saturated at the
time it reaches the engine cylinder. Superheated steam may be
secured by passing saturated steam through coils of pipe 'in the
path of the hot flue gases from the boiler to the chimney. An
apparatus for superheating steam is called a superheater.

The pressure of steam will remain constant if it is used as fast
as it is generated. If an engine uses steam too rapidly the boiler
pressure will drop, and similarly if the fuel is burned at a constant
rate and an insufficient amount of steam is used the pressure of
the steam in the boiler will increase.

Steam Tables. — In Table 5 are given some of the most impor-
tant properties of saturated steam, which include:

1. Pressure of steam in pounds per square inch absolute (p).
This column gives the total pressure exerted and is the sum of the
gage pressure which measures the pressures above that of the
atmosphere and the atmospheric pressure as indicated by the
barometer. A barometric reading of 30 inches corresponds to a
pressure of 14.7 pounds per square inch.

Table 5. — Properties of Saturated Steam

(Marks and Davis)
ENGLISH UNITS

m O
5°*

turn

Specific

Volume

Cu. Ft. per

Pound

Ill

Si*

.0886

1072.6

3301.0

.000303

.0886

.2562

28.1

1057.4

1085.5

1207.5

.000828

.2562

.5056

48.1

1046.6

1094.7

635.4

.001573

.5056

101.8

69.8

1034.6

1104.4

333.00

.00300

126.1

94.1

1021.4

1115.5

173.30

.00577

141.5

109.5

1012.3

1121.8

118.50

.00845

153.0

120.9

1005.6

1126.5

90.50

.01106

162.3

130.2

1000.2

1130.4

73.33

.01364

170.1

138.0

995.7

1133.7

61.89

.01616

176.8

144.8

991,7

1136.5

53.58

.01867

182.9

150.8

988.1

1138.9

47.27

.02115

STEAM AND GAS POWER ENGINEERING

Properties of Saturated Steam — Continued

ENGLISH UNITS

8 •

&£

8 1

■

4*3

§a

-£ c3 O
(JO

Specific

Volume

Cu. Ft. per

Pound

tigs
ftjo

11*

(-I'D .
PhAcJ

t .

188.3

156.3

984.8

1141.1

42.36

.02361

193.2

161.2

981.8

1143.0

38.38

.02606

197.7

165.8

979.0

1144.8

35.10

.02849

202.0

170.0

976.4

1146.4

32.38

.03089

205.9

173.9

974.0

1147.9

30.04

.03329

209.6

177.6

971.7

1149.3

28.02

.03568

14.7

212.0

180.1

970.4

1150.4

26.79

.03733

14.7

213.0

181.1

969.5

1150.6

26.27

.03806 •

216.3

184.5

967.4

1151.9

24.77

.04042

219.4

187.7

965.4

1153.1

23.38

.04277

222.4

190.6

963.5

1154.1

22.16

.04512

225.2

193.5

961.6

1155.1

21.07

.04746

228.0

196.2

959.8

1156.0

20.08

.04980

230.6

198.9

958.0

1156.9

19.18

.05213

233.1

201.4

956.4

1157.8

18.37

.05445

235.5

203.9

954.8

1158.7

17.62

.05676

237.8

206.2

953.2

1159.4

16.93

.05907

240.1

208.5

951.7

1160.2

16.30

.0614

242.2

210.7

950.3

1161.0

15.71

.0636

244.4

212.8

948.9

1161.7

15.18

.0659

246.4

214.9

947.5

1162.4

14.67

.0682

248.4

217.0

946.1

1163.1

14.19

.0705

250.3

218.9

944.8

1163.7

13.74

.0728

252.2

220.8

943.5

1164.3

13.32

.0751

254.1

222.7

942.2

1164.9

12.93

.0773

255.8

224.5

941.0

1165.5

12.57

.0795

257.6

226.3

939.8

1166.1

12.22

.0818

259.3

228.0

938.6

1166.6

11.89

.0841

261.0

229.7

937.4

1167.1

11.58

.0863

262.6

231.4

936.3

1167.7

11.29

.0886

264.2

233.0

935.2

1168.2

11.01

.0908

265.8

234.6

934.1

1168.7

10.74

.0931

267.3

236.2

933.0

1169.2

10.49

.0953

268.7

237.7

931.9

1169.6

10.25

.0976

270.2

239.2

930.9

1170.1

10.02

.0998

271.7

240.6

929.9

1170.5

9.80

.1020

273.1

242.1

928.9

1171.0

9.59

.1043

45 -

274.5

243.5

927.9

1171.4

9.39

.1065

275.8

244.9

926.9

1171.8

9.20

.1087

STEAM

Properties op Saturated Steam — Continued

ENGLISH UNITS

h) o

o a

3 J

Specific

Volume

Cu. Ft. per

Pound

IT-

277.2

246.2

926.0

1172.2

9.02

.1109

278.5

247.6

925.0

1172.6

8.84

.1131

279.8

248.9

924.1

1173.0

8.67

.1153

281.0

250.2

923.2

1173.4

8.51

.1175

282.3

251.5

922.3

1173.8

8.35

.1197

283.5

252.8

921.4

1174.2

8.20

.1219

284.7

254.0

920.5

1174.5

8.05

.1241

285.9

255.2

919.6

1174.8

7.91

.1263

287.1

256.4

918.7

1175.1

7.78

.1285

288.2

257.6

917.9

1175.5

7.65

.1307

289.4

258.8

917.1

1175.9

7.52

.1329

290.5

259.9

916.2

1176.1

7.40

.1351

291.6

261.1

915.4

1176.5

7.28

.1373

292.7

262.2

914.6

1176.8

7.17

.1394

293.8

263.3

913.8

1177.1

7.06

.1416

294.9

264.4

913.0

1177.4

6.95

.1438

295.9

265.5

912.2

1177.7

6.85

.1460

297.0

266.5

911.5

1178.0

6.75

.1482

298.0

267.6

910.7

1178.3

6.65

.1503

299.0

268.6

910.0

1178.6

6.56

.1525

300.0

269.7

909.2

1178.9

6.47

.1547

301.0

270.7

908.4

1179.1

6.38

.1569

302.0

271.7

907.7

1179.4

6.29

.1591

302.9

272.7

906.9

1179.6

6.20

.1612

303.9

273.7

906.2

1179.9

6.12

.1634

304.8

274.6

905.5

1180.1

6.04

.1656

305.8

275.6

904.8

1180.4

5.96

.1678

306.7

276.6

904.1

1180.7

5.89

.1699

307.6

277.5

903.4

1180.9

5.81

.1721

308.5

278.5

902.7

1181.2

5.74

.1743

309.4

279.4

902.1

1181.5

5.67

.1764

310.3

280.3

901.4

1181.7

5.60

.1786

311.2

281.2

900.7

1181.9

5.54

.1808

312.0

282.1

900.1

1182.2

5.47

.1829

312.9

283.0

899.4

1182.4

5.41

.1851

313.8

283.8

898.8

1182.6

5.34

.1873

314.6

284.7

898.1

1182.8

5.28

.1894

315.4

285.6

897.5

1183.1

5.22

.1915

316.3

286.4

896.9

1183.3

5.16

.1937

STEAM AND GAS POWER ENGINEERING

Phoperties of Saturated Steam — Continued

ENGLISH UNITS

o5 §M
.2 ft

2 •
fft,

Is
£ s
fj

la
m

+> 1

.2W
h? 8

<o 8

cSCQ

Specific

Volume

Cu. Ft. per

Pound

§ g 3

02 O -1

317.1

287.3

896.2

1183.5

5.10

.1959

317.9

288.1

895.6

1183.7

5.05

.1980

318.7

288.9

895.0

1183.9

5.00

.2002

319.5

289.8

894.3

1184.1

4.94

.2024

320.3

290.6

893.7

1184.3

4.89

.2045

321.1

291.4

893.1

1184.5

4.84

.2066

321.8

292.2

892.5

1184.7

4.79

.2088

322.6

293.0

891.9

1184.9

4.74

.2110

323.4

293.8

891.3

1185.1

4.69

.2131

324.1

294.5

890.7

1185.2

4.65

.2152

324.9

295.3

890.1

1185.4

4.60

.2173

325.6

296.1

889.5

1185.6

4.56

.2194

326.4

296.8

889.0

1185.8

4.51

.2215

327.1

297.6

888.4

1186.0

4.47

.2237

100

327.8

298.4

887.8

1186.2

4.430

.2257

100

101

328.6

299.1

887.2

1186.3

4.389

.2278

101

102

329.3

299.8

886.7

1186.5

4.349

.2299

102

103

330.0

300.6

886.1

1186.7

4.309

.2321

103

101

330.7

301.3

885.6

1186.9

4.270

.2342

104

105

331.4

302.0

885.0

1187.0

4.231

.2364

105

106

332.0

302.7

884.5

1187.2

4.193

.2385

106

107

332.7

303.4

883.9

1187.3

4.156

.2407

107

108

333.4

304.1

883.4

1187.5

4.119

.2428

108

109

334.1

304.8

882.8

1187.6

4.082

.2450

109

110

334.8

305.5

882.3

1187.8

4.047

.2472

110

111

335.4

306.2

881.8

1188.0

4.012

.2493

111

112

336.1

306.9

881.2

1188.1

3.977

.2514

112

113

336.8

307.6

880.7

1188.3

3.944

.2535

113

114

337.4

308.3

880.2

1188.5

3.911

.2557

114

114.7

337.9

308.8

879.8

1188.6

3.888

.2572

114.7

115

338.1

309.0

879.7

1188.7

3.878

.2578

115

116

338.7

309.6

879.2

1188.8

3.846

.2600

116

117

339.4

310.3

878.7

1189.0

3.815

.2621

117

118

340.0

311.0

878.2

1189.2

3.784

.2642

118

119

340.6

311.7

877.6

1189.3

3.754

.2663

119

120

341.3

312.3

877.1

1189.4

3.725

.2684

120

121

341.9

313.0

876.6

1189.6

3.696

.2706

121

122

342.5

313.6

876.1

1189.7

3.667

.2727

122

123

343.2

314.3

875.6

1189.9

3.638

.2749

123

STEAM

Properties op Saturated Steam — Continued

ENGLISH UNITS

3 v

11*

3Em

e
A

fill

►3o

Specific

Volume

Cu. Ft. per

Pound

§ O 3

o5 g^

124

343.8

314.9

875.1

1190.0

3.610

.2770

124:

125

344.4

315.5

874.6

1190.1

3.582

.2792

125

126

345.0

316.2

874.1

1190.3

3.555

.2813

126

127

345.6

316.8

873.7

1190.5

3.529

.2834

127

128

346.2

317.4

873.2

1190.6

3.503

.2855

128

129

346.8

318.0

872.7

1190.7

3.477

.2876

129

130

347.4

318.6

872.2

1190.8

3.452

.2897

130

131

348.0

319.3

871.7

1191.0

3.427

.2918

131

132

348.5

319.9

871.2

1191.1

3.402

.2939

132

133

349.1

320.5

870.8

1191.3

3.378

.2960

133

134

349.7

321.0

870.4

1191.4

3.354

.2981

134

135

350.3

321.6

869.9

1191.5

3.331

.3002

135

136

350.8

322.2

869.4

1191.6

3.308

.3023

136

137

351.4

322.8

868.9

1191.7

3.285

.3044

137

138

352.0

323.4

868.4

1191.8

3.263

.3065

138

139

352.5

324.0

868.0

1192.0

3.241

.3086

139

140

353.1

324.5

867.6

1192.1

3.219

.3107

140

141

353.6

325.1

867.1

1192.2

3.198

.3128

141

142

354.2

325.7

866.6

1192.3

3.176

.3149

142

143

354.7

326.3

866.2

1192.5

3.155

.3170

143

144

355.3

326.8

865.8

1192.6

3.134

.3191

144

145

355.8

327.4

865.3

1192.7

3.113

.3212

145

146

356.3

327.9

864.9

1192.8

3.093

.3233

146

147

356.9

328.5

864.4

1192.9

3.073

.3254

147

148

357.4

329.0

864.0

1193.0

3.053

.3275

148

149

357.9

329.6

863.5

1193.1

3.033

.3297

149

150

358.5

330.1

863.1

1193.2

3.013

.3319

150

152

359.5

331.2

862.3

1193.5

2.975

.3361

152

154

360.5

332.3

861.4

1193.7

2.939

.3403

154

156

361.6

333.4

860.5

1193.9

2.903

.3445

156

158

362.6

334.4

859.7

1194.1

2.868

.3487

158

160

363.6

335.5

858.8

1194.3

2.834

.3529

160

162

364.6

336.6

858.0

1194.6

2.801

.3570

162

164

365.6

337.6

857.2

1194.8

2.768

.3613

164

166

366.5

338.6

856.4

1195.0

2.736

.3655

166

168

367.5

339.6

855.5

1195.1

2.705

.3697

168

170

368.5

340.6

854.7

1195.3

2.674

.3739

170

172

369.4

341.6

853.9

1195.5

2.644

.3782

172

174

370.4

342.5

853.1

1195.6

2.615

.3824

174

176

371.3

343.5

852.3

1195.8

2.587

.3865

176

STEAM AND GAS POWER ENGINEERING

Properties op Saturated Steam
english units

Concluded

Jr'a .
3*

0) ,

a ho

■*» 3

CJ.J

c3 A
D 5 m

■B *.2
A o

<u a
n 1

Specific

Volume

Cu. Ft. per

Pound

Is 3
Qgo

Sa •

figj4

178

372.2

344.5

851.5

1196.0

2.560

.3907

178

180

373.1

345.4

850.8

1196.2

2.532

.3949

180

182

374.0

346.4

850.0

1196.4

2.506

.3990

182

184

374.9

347.4

849.3

1196.7

2.480

.4032

184

186

375.8

348.3

848.5

1196.8

2.455

.4074

186

188

376.7

349.2

847.7

1196.9

2.430

.4115

188

190

377.6

350.1

847.0

1197.1

2.406

.4157

190

192

378.5

351.0

846.2

1197.2

2.381

.4200

192

194

379.3

351.9

845.5

1197.4

2.358

.4242

194

196

380.2

352.8

844.8

1197.6

2.335

.4284

196

198

381.0

353.7

844.0

1197.7

2.312

.4326

198

200

381.9

354.6

843.3

1197.9

2.289

.4370

200

202

382.7

355.5

842.6

1198.1

2.268

.4411

202

204

383.5

356.4

841.9

1198.3

2.246

.4452

204

206

384.4

357.2

841.2

1198.4

2.226

.4493

206

208

385.2

358.1

840.5

1198.6

2.206

.4534

208

210

386.0

358.9

839.8

1198.7

2.186

.4575

210

212

386.8

359.8

839.1

1198.9

2.166

.4618

212

214

387.6

360.6

838.4

1199.0

2.147

.4660

214

216

388.4

361.4

837.7

1199.1

2.127

.4700

216

218

389.1

362.3

837.0

1199.3

2.108

.4744

218

220

389.9

363.1

836.4

1199.5

2.090

.4787

220

222

390.7

363.9

835.7

1199.6

2.072

.4829

222

224

391.5

364.7

835.0

1199.7

2.054

.4870

224

226

392.2

365.5

834.3

1199.8

2.037

.4910

226

228

393.0

366.3

833.7

1200.0

2.020

.4950

228

230

393.8

367.1

833.0

1200.1

2.003

.4992

230

232

394.5

367.9

832.3

1200.2

1.987

.503

232

234

395.2

368.6

831.7

1200.3

1.970

.507

234

236

396.0

369.4

831.0

1200.4

1.954

.511

236

238

396.7

370.2

830.4

1200.6

1.938

.516

238

240

397.4

371.0

829.8

1200.8

1.923

.520

240

242

398.2

371.7

829.2

1200.9

1.907

.524

242

244

398.9

372.5

828.5

1201.0

1.892

.528

244

246

399.6

373.3

827.8

1201.1

1.877

.532

246

248

400.3

374.0

827.2

1201.2

1.862

.537

248

250

401.1

374.7

826.6

1201.3

1.848

.541

250

275

409.6

383.7

819.0

1202.7

1.684

.594

275

300

417.5

392.0

811.8

1203.8

1.547

.647

300

350

431.9

407.4

798.5

1205.9

1.330

.750

350

STEAM 29

2. Temperatures of saturated steam in degrees Fahrenheit (t).
This column of temperatures shows the vaporization tempera-
ture, or the boiling point, at each of the given pressures.

3. Heat of the liquid (h), or the heat required to bring up
the temperature of a pound of water from freezing point to boiling
point at the given pressure.

4. The latent heat (L), or the heat required to vaporize a
pound of water into dry steam at the given pressure, after the
boiling point is reached.

5. The total heat of the steam (H), which is the sum of the
heat of the liquid and the latent heat, and represents the total heat
that is required to generate dry saturated steam from water at the
freezing point, at the various pressures.

6. The volume of 1 pound of dry steam (v) at the various
pressures.

7. Density of dry steam in pounds per cubic foot (- ) •

To illustrate the use of the steam tables the following examples
will be solved:

Example 1. — Water at 200°F. is fed to a boiler in which the pressure is
100 pounds per square inch gage. How much heat must be supplied by the
fuel to evaporate each pound of water into dry steam ?

Solution. — A pressure of 100 pounds per square inch gage = 100 + 14.7
= 114.7 pounds per square inch absolute, if the barometer reading is 30
in.

The heat required to evaporate one pound of water from freezing point
into dry steam at a pressure of 114.7 lb. per square inch absolute is the
total heat of steam (H) at the pressure, or 1188.6.

Since the water fed to the boiler has a temperature of 200°F., the total
amount of heat to be supplied by the fuel to evaporate one pound of water
into dry steam is:

1 188.6 - (200 - 32) = 1020.6 B.t.u.

Example 2. — If the steam in example 1, contained 3 per cent, moisture,
calculate the heat which must be supplied by the fuel to evaporate each
pound from feed water at 200°F.

Solution. — The heat of the liquid, or the heat required to raise the tem-
perature of a pound of water from 200°F. to the boiling point corresponding
to a pressure of 114.7 pounds per square inch absolute is:
308.8 - (200 - 32) = 140.8 B.t.u.

The heat required to vaporize a pound of water into dry steam at 114.7
pounds per square inch absolute, after the boiling point is reached, is 879.8
B.t.u.

30 STEAM AND GAS POWER ENGINEERING

Since the steam in this example contains 3 per cent moisture, it is 97 per
cent, dry, and the heat required to vaporize it is :
879.8 X 0.97 = 853.4 B.t.u.
The total heat required to change one pound of water at 200° F. into
steam, 3 per cent, wet, and at a pressure of 114.7 pounds per square inch
absolute is :

140.8 + 853.4 = 994.2 B.t.u.
Example 3. — What is the volume of one pound of steam at 150 lbs. per
square inch absolute, if it is 20 per cent, wet?

Solution. — Dry steam at a pressure of 150 lbs. per sq. in. absolute has a
volume of 3.013 cu. ft. per pound.

The volume of one pound of steam which is 20 per cent, wet, or 80 per
cent, dry, at a pressure of 150 pounds per square inch absolute is:
3.013 X 0.80 = 2.41 cubic feet.

Determination of the Quality of Steam.— The quality, or the
per cent, of moisture in saturated steam, is determined by means
of a calorimeter. There are three types of steam calorimeters
in general use,- — the Throttling Calorimeter, the Separating
Calorimeter, and the Electrical Calorimeter.

The throttling calorimeter is the most accurate instrument
for measuring the amount of moisture in steam. This instrument
depends for its action upon the fact that steam, nearly dry,
becomes superheated when its pressure is reduced by throttling,
since saturated steam at high pressure contains more heat than
at low pressure. A simple type of throttling calorimeter is
illustrated in Fig. 6. 0 is the orifice discharging into the chamber
C, into which a thermometer T is inserted. A mercury manome-
ter is attached at Vs.

Let Pi equal the absolute pressure of the steam in the main
steam pipe. The heat contained in one pound of steam at the
pressure Pi would be the sum of the heat of the liquid (hi) and
the latent heat of steam (Lx) corrected for the moisture, or

hi + xLi

where x is the quality of the steam.

If the steam has a pressure P2, as indicated by the manometer,
attached to Vz, after it passes the orifice 0, and a temperature
ts, as registered by the thermometer T, the heat contained
in one pound of steam at the pressure P2 would be the total
heat (Hz) of dry saturated steam at the lower pressure plus the heat

STEAM

due to the superheat. The heat due to the superheat is calcu-
lated by multiplying the degrees of superheat by the specific
heat of superheated steam at the given pressure and temperature.
By specific heat is meant the resistance which a substance offers
to a change in its temperature. The average value of the specific
heat of superheated steam (CP) at the temperatures and pressures
common in calorimeters is 0.4,7. The degrees of superheat
are determined by subtracting the saturated temperature (t2)
corresponding to the lower pressure, as measured by the

Fig. 6. — Throttling steam calorimeter.

manometer at Vz, from the temperature t8, as indicated by the
thermometer T of the steam calorimeter.

Since the total heat in the steam is the same on both sides
of the calorimeter:

hi + xU = H2 + 0.47ft, - h)
Solving for x, the quality of steam is calculated as follows :
#2 + 0.47 (t, - U) - ^

x =

32 STEAM AND GAS POWER ENGINEERING

Example. — Steam is tested by means of a throttling calorimeter. Find
the per cent, of moisture in the steam if the gage pressure of the 3team in the
main steam pipe is 115.3, the pressure in the calorimeter, as indicated by the
manometer at Vz (Fig. 6), two inches of mercury, and the temperature of
the calorimeter thermometer at T (Fig. 6) 260°F.

Solution. — Pi = 115.3 + 14.7 = 130 pounds per square inch absolute.
h = 318.6
Li - 872.2
P2 = 14.7 + (2 X 0.491) = 15.68. (One inch of mercury is

equal to 0.491 pounds pressure per square inch.)
H2 = 1151.4
t2 = 215.3

_ 1151.4 + 0.47 (260 - 215.3) - 318.6
x - g^^ - °-978

Per cent, of moisture = 100 — 97.8 = 2.2

The throttling calorimeter is unsuitable for measuring the
quality of steam which contains more than 3 or 4 per cent,
moisture.

The amount of moisture in very wet steam can best be deter-
mined by a separating calorimeter, illustrated in Fig. 7. Steam
enters the separating calorimeter at A (Fig. 7), passes down the
vertical pipe, plugged at the lower end, from which it escapes
through a large number of holes as indicated. The moisture col-
lects at the bottom of the vessel V and can be measured by the
calibrated glass gage G. The steam leaves the calorimeter at N
and can be collected, condensed and weighed. The gage P
indicates the pressure in the jacket J. This pressure is roughly
proportional to the flow of steam through the nozzle N. The
gage P is usually provided with a scale to indicate the approxi-
mate flow of steam. The per cent, of moisture is calculated
by dividing the weight of water collected in the gage glass G
by the sum of the weights of steam passing out at N and of the
water at G.

The electrical calorimeter consists of an electric heater which
is used for drying and for superheating the steam. The amount
of electric energy required to dry the steam is proportional to
the amount of moisture in the steam.

Problems
1. A boiler generates steam at a pressure of 120 pounds by the gage. If
the barometric pressure is 28.5 in., calculate the absolute pressure in pounds
per square inch.

STEAM

2. Calculate the heat required to change 20 pounds of water at a tempera-
ture of 190°F. into dry steam at 150 pounds per square inch absolute.

3. If the steam in problem 2 contains 5 per cent, moisture, calculate the
heat required.

4. Compare the volumes of one pound of steam at the following pressures
in pounds per square inch absolute: >£, 1, 2, 14.7, 100, 150, 200, 300.

Fig. 7. — Separating calorimeter.

5. A plain cylindrical boiler has a diameter of 30 inches and a length of
12 feet. If two-thirds of the volume of the boiler is filled with water at a
temperature of 270°F., the other third with steam, calculate:

(a) Boiler pressure in pounds per square inch gage if the barometer is
29.2 inches.
3

34 STEAM AND GAS POWER ENGINEERING

(b) Calculate the weight of the water and the weight of the steam, con-
tained in the boiler.

6. The quality of steam at a pressure of 140 pounds per square inch
gage is measured by means of a throttling calorimeter. If the calorimeter
thermometer reads 270°F. and the manometer registers 3 inches of mercury,
calculate the quality of the steam.

7. Prove that the throttling calorimeter will be unsuitable for measuring
the quality of steam which has 10 per cent, moisture at a steam pressure of
150 pounds per square inch gage.

8. Steam is tested by means of a separating calorimeter (Fig. 7) and gives
the following results :

Water collected in the glass gage G 0 . 25 lb.

Steam collected at iV 0. 90 lb.

Calculate the quality of the steam.

CHAPTER IV
BOILERS

The function of a boiler is to generate steam to be used either
in engine cylinders, or for heating purposes. The term boiler
is commonly applied to the combination of the furnace in which
the fuel is burned and the boiler proper, which is a closed vessel
containing water and steam.

Classification of Boilers. — Boilers are divided into two classes,
the fire-tube and the water-tube. In the fire-tube boiler (Fig. 9)
the hot gases developed by the combustion of the fuel pass
through the tubes, while in the water-tube boiler (Fig. 18) these
gases pass around the tubes. Either type may be constructed
as a vertical or as a horizontal boiler, depending on whether the
axis of the shell is vertical or horizontal.

The fire-tube boiler may be externally or internally fired. In
the externally fired boiler (Fig. 10) the furnace is in the brick
setting entirely outside of the boiler shell, while in the internally
fired types (Figs. 13 and 14) the furnace is in the boiler shell,
no brick setting being necessary. For stationary work the
externally fired boiler is the most common, while the internally
fired types are always used for locomotive and traction engine
purposes, and generally for marine power plants. Vertical
fire-tube boilers are usually internally fired.

Plain Cylindrical Boiler. — The plain cylindrical type of boiler
is practically obsolete, but it is of interest because of its simplicit}'.
Fig. 8 illustrates a longitudinal cross-section of such a boiler.
It consists of a cylindrical shell closed at its two ends by dished
heads. Because of the circular shaped heads, no staying is
necessary. The chief disadvantage in the use of this type of
boiler is the small amount of heating surface it contains, which
means that an extremely large boiler is necessary for small
evaporative effects.

STEAM AND GAS POWER ENGINEERING

Horizontal Return Tubular Boiler. — Boilers of this type
are most commonly used in this country. They are simple,
inexpensive, have a large overload capacity, and are economical

^^^^^^^^^l^^^^^^^^^^^^^

Fig. 8. — Plain cylindrical boiler.

when properly handled. The general appearance of a return
tubular boiler is shown in Fig. 9. Fig. 10 illustrates the details
of the setting.

These boilers consist of a cylindrical shell closed at the ends

Return tubular boiler.

by two flat heads, and of numerous small fire tubes which extend
the whole length of the shell. The fire tubes are three or four
inches in diameter and 14 to 18 feet long. About two-thirds of
the volume of the shell is filled with water, the other third,

BOILERS

called the steam space, being left for the disengagement of the
steam from the water. The water line is about six inches above
the top row of fire tubes. Sometimes, as shown in Fig. 11, a

Fig. 10. — Details of boiler setting.

steam dome D is provided to increase the volume of the steam
space. Steam domes are seldom used in modern boilers for
stationary power plants, as they weaken the boiler shell and add
to the first cost of the boiler.

Fia. 11. — Boiler with dome.

The coal is burned upon the grates which, as shown in Fig. 10,
rest upon the bridge wall W and upon the front of the setting.
The hot gases, formed by the combustion of the fuel, pass from
the furnace under and along the boiler shell to the back connec-
tion, or combustion chamber C, from there to the front through

STEAM AND GAS POWER ENGINEERING

the tubes, and up the uptake to the breeching or flue, which leads
to the chimney.

The distance between the grates and the boiler shell should be
greater for bituminous than for anthracite coal. This distance,
in the case of the best anthracite coal, may be as little as 24
inches, but for bituminous coal the distance between the grates
and the boiler should be more than 36 inches. The greater this
distance the more opportunity will be given for the proper com-
bustion of the fuel.

This type of boiler is usually provided with a hand-hole or a
man-hole in front below the tubes, and with a man-hole in the top
of the boiler.

4 $

Triangular
Loop

Fig. 12. — Independent method of setting boiler.

The flat heads, or tube sheets of the boiler, are stayed below
the water line by the tubes. Above the water line special stays
must be provided to prevent the tube sheets from distorting.
In Fig. 9 the distortion of the tube sheet above the tubes is pre-
vented by the use of diagonal stays which transfer the strain to
the shell of the boiler.

Boilers of this type are usually set in brick settings. In some
cases the boiler is supported by brackets, as shown in Fig. 10.
In this case the front brackets rest on metal plates embedded in
the brickwork of the side walls, while the back brackets are placed
on rollers, which in turn rest on horizontal plates, this method
allowing the back of the boiler to move as the shell expands or

BOILERS 39

contracts. A better method is to support the boiler independent
of the setting, on steel framework, as shown in Fig. 12.

The setting should be constructed so that the hot gases will not
come in contact with the shell above the water line.

Scotch Marine Boiler. — -A single ended, two furnace Scotch
marine boiler is shown in Fig. 13. This boiler differs from
those previously described in that it is internally fired. The
boiler consists of a cylindrical shell enclosed at its two ends
by flat plates. The furnace flues are connected to a combus-
tion chamber. Numerous fire tubes fill the upper portion of the
boiler. The travel of gases is first through the furnace-flues,
then to the combustion chamber, and finally through the tubes
to the uptake and stack.

Boilers of this type are self contained, require little overhead
room, and no setting. The rear surface of the combustion cham-
ber is stayed by connecting it to the rear head by means of short
bolts, termed stay bolts. The front surface of the combustion
chamber is stayed by the furnace flues and the tubes, while the
top of the chamber is supported by a bar which transmits the
strain to the two side sheets and is termed a girder stay. The
heads of the boiler above the tubes are supported by through
stays, which are rods connecting both heads as shown. Large
boilers of this type are provided with furnaces at both ends
which open into a common combustion chamber in the middle
of the boiler.

Locomotive Boiler. — Fig. 14 illustrates a locomotive boiler.
A type similar to the one shown is used in stationary work.
The stationary type, however, is only made in comparatively
small sizes and finds its application only in isolated locations, or
where steam is required temporarily. The type used in loco-
motive practice as well as that used in stationary work is classified
as a fire-tube, internally fired boiler.

The locomotive boiler consists of a cylindrical shaped barrel
or shell which contains a large number of fire-tubes. The
furnace or fire-box is constructed by extending the shell down-
ward to form the sides. The walls of the fire-box are made
double, the space thus created being connected to the water space
in the shell. This extension of the plates to form the sides of the
fire-box produces two narrow sections which are filled with water,

STEAM AND GAS POWER ENGINEERING

BOILERS

forming what is usually
termed a water leg. These
boilers are constructed with
a steam dome from which
the steam is taken.

The hot gases leave the
furnace, pass through the
small tubes to the smoke
box at the front of the
boiler, and from there to
the stack.

The flat sheets compos-
ing the water legs are
stayed by the use of small
stay bolts. The same
method of staying is ap-
plied to the sheet forming
the top of the fire box,
but in this case the name
" crown stays" is usually
applied.

Vertical Fire-tube Boil-
ers.— Two forms of vertical
boilers are shown in Figs.
15 and 16. In the form
shown in Fig. 15 the tops
of the tubes are above the
water line, and may become
overheated when the boiler
is forced. To prevent in-
jury from this cause, some
forms of vertical boilers are
constructed as shown in
Fig. 16, the tops of the
tubes being ended in a sub-
merged tube sheet, which
is kept below the water
line.

The essential parts of all
forms of vertical boilers
are a cynndrical shell with
a fire-box and ash pit in

STEAM AND GAS POWER ENGINEERING

the lower end. The tubes lead directly from the furnace to
the upper head of the shell. The hot gases from the furnace
pass through the tubes and out of the stack.

Vertical boilers occupy little floor space, require no setting
except a light foundation, and are inexpensive. To offset
these advantages, vertical boilers, as ordinarily constructed, are

Fig. 15.

-Vertical boiler exposed
tube type.

Fig. 16.

Vertical boiler submerged
tube type.

uneconomical, have small capacity, have too little space for the
disengagement of the steam, and are inaccessible for thorough
inspection and cleaning.

Fig. 17 illustrates one of the larger vertical boilers, known as
the Manning type. The tubes in this boiler are much longer
than those usually installed in vertical boilers of the types pre-
viously discussed, consequently the heating surface is greatly
increased. The shell is enlarged at the fire-box to provide for a
larger furnace and more grate area. No staying is required in

BOILERS 43

this boiler except at the water leg, and at this point the inner
sheet of the fire-box is joined to the outer shell by stay bolts.

<-..._
^^^^■1

Fig. 17. — Manning vertical boiler.

Water Tube Boilers. — Water tube boilers are used in large
power plants on account of their adaptability to higher steam

STEAM AND GAS POWER ENGINEERING

pressures and larger sizes, decreased danger from serious explo-
sions, greater space economy, and rapidity of steam generation.
For small power plants and for steam pressures of 125 pounds or
less the fire tube boiler is usually more suitable on account of its
lower first cost. Also in a fire-tube boiler, if a tube should break,
the boiler can be repaired by plugging without seriously interrupt-
ing service, which is not the case with most types of water tube

Fig. 18. — Babcock and Wilcox Boiler.

boilers. As far as efficiency is concerned, numerous tests show
that either type, when properly designed and operated, will give
the same economy.

There are many different types of water tube boilers, but the
essential parts of all are much the same. They consist of nu-
merous tubes filled with water, and one or more drums for the dis-
engagement of the steam from the water. No tubes run through

BOILERS 45

the drums, consequently dished heads may be used, thus elimi-
nating the necessity for staying.

The Babcock & Wilcox Boiler.- — Fig. 18 shows the Babcock
and Wilcox type of water tube boiler. This boiler consists of
a number of straight tubes fastened into several sets of headers
which are connected to a common drum. The feed water enters
the boiler through a pipe passing through the front end of the
drum and extending back about one-third of its length. Oppo-
site the end of each tube there is provided a hand hole through
which the tubes may be inspected or cleaned. The hot gases from
the furnace are deflected by means of fire brick baffle plates and
the bridge wall and pass across the tubes three times before reach-
ing the uptake at the rear of the boiler. In some cases the baffling
is arranged so that the gases are directed along the tubes. The
boiler is supported by steel beams resting on columns independent
of the setting.

The Heine Boiler. — The Heine boiler is illustrated in Fig. 19.
It consists of a number of straight tubes, expanded into two water
legs or headers of flanged steel plate, which are connected to a
common drum. The tubes are parallel to the drum. Opposite
the end of each tube is a hand hole to facilitate cleaning and in-
spection. The feed water enters the boiler through the front
head, passes into a mud drum, where the impurities are deposited,
circulates from the front toward the back in the drum, and from
the back toward the front in the tubes. The baffle plates in
this type of boiler are usually arranged horizontally so that the
hot gases pass first to the rear of the boiler, then back through
the nest of tubes to the front, and finally back to the stack,
coming in contact with the drum of the boiler in this last pass.
This boiler is supported independently of the setting at the front
end, while the rear water leg rests upon the rear wall.

Stirling Boiler. — Fig. 20 shows a sectional elevation of a Stirling
water tube boiler. This boiler consists of four horizontal cylin-
drical drums, three at the top and one large drum at the bottom.
A series of inclined water tubes connect the upper drums with the
lower. Tubes are used to connect the steam spaces of the upper
drums so that any steam formed in these may be transmitted to
the middle drum. Similarly a series of tubes connects the front
and middle drums below the water line. Such a connection

STEAM AND GAS POWER ENGINEERING

limits the main circulation within the boilers to the front and
middle bank of tubes.

The feed water enters the rear upper drum, flows downward
through the rear bank of tubes to the bottom drum, where the im-
purities are deposited, and then upward through the front bank
of tubes. The rear system of tubes acts as a feed water heater.

Fig. 19.— Heine boiler.

The steam formed during the passage upward through the front
tubes becomes separated from the water in the front drum and
passes into the middle drum, which is connected with the steam
main. The safety valve is located on the top of the middle drum.
The baffle walls are set so that the hot gases from the furnace
pass over the bridge wall, and thence upward through the first

BOILERS

bank of tubes. It then passes downward through the second
set of tubes, and finally upward through the remaining set to
the stack. Thus the water and hot gases circulate in opposite
directions.

Wickes Boiler. — Fig. 21 illustrates the Wickes vertical water
tube boiler. This boiler consists primarily of two cylinders

Stirling water tube boiler.

joined together by straight tubes. The tubes are divided into
two sets by a baffle wall which passes through their center. The
whole boiler is erected in a vertical position and is surrounded
by brickwork.

The gases generated in the furnace pass upward through the
forward compartment, and are directed downward through the
rear compartment. The hotter gases thus come in contact with
the front tubes, while the cooler gases surround those at the rear.

STEAM AND GAS POWER ENGINEERING

This causes the main circulation within the boiler to be upward
through the front and downward through the rear compartment.
Parker Down Flow Boiler. — The Parker boiler is illustrated in
Fig. 22, and consists of a cylindrical drum inside of which is a
diaphragm separating the steam space from the water space.

Fig. 21. — Wickes vertical boiler.

The tubes are arranged to form a series of continuous passages,
termed elements, leading downward from the water chamber, and
are finally directed upward from the bottom ends to the steam
chamber. A check valve at the top of each element prevents the
reversal of flow. The straight tubes form the continuous ele-
ments by expanding them into junction boxes, which are pro-
vided with a hand-hole opening opposite each tube.

BOILERS

The water fed into the drum seeks its level in the elements.
When heat is applied the water in the elements is soon discharged
as steam, into the drum. The water then runs down from the
drum in an effort to retain its level which is made impossible
by the continuous evaporation. As a result, there is a rapid
flow of water and steam downward through the tube elements
impelled by the gravity head of water.

Fig. 22. — Parker down-flow boiler.

The locations of the tube elements and of the baffle walls are
arranged in such a manner that the gases and water circulate
in opposite directions. This principle brings the hottest steam
in contact with highly heated gases, and steam at the lower tem-
perature in contact with cooler gases.

This boiler as in the case of most of the others of the water-
tube type is supported independently of the boiler setting.

Marine Water Tube Boilers. — The service to which a boiler
is to be applied modifies its design. Several types of water
tube boilers have been designed and have been found well adapted
to marine work. The main requirements for a successful boiler in

STEAM AND GAS POWER ENGINEERING

this class of service are that it should occupy little space and
have a large evaporative capacity.

Fig. 23 illustrates a water-tube boiler of the Babcock and
Wilcox type, designed for marine service. It consists of a

Fig. 23. — Babcock and Wilcox Marine boiler.

cylindrical drum whose axis is at right angles to those of the
tubes, or is crossed. The tubes are connected to headers, but
the size of these tubes is smaller and the number of them larger
than is common in the stationary type.

Materials.- — Boilers intended for power purposes are made of

BOILERS 51

rolled steel plates riveted together. Steel is the most desirable
material for the construction of a boiler because of its strength
and cheapness, and also because of its ductility, which permits
the material to be formed into the irregular shapes necessary
in constructing the boiler. Boiler tubes are made of steel and
are usually lap welded.

Cast iron is not generally considered a suitable material. It is
brittle, possesses practically no ductility, and often produces
unsound castings. It is used only in the construction of house
heating boilers, as in this class of service high pressures are not
necessary.

Copper is used in boiler construction in special cases, as in fire
engine boilers, where the use of a material of less strength and
greater cost is permissible in order to obtain a quick steaming
boiler.

Heating Surface. — The heating surface of a boiler is that
surface which is exposed to the flame and hot gases. This
term is expressed in square feet, and the general rule employed in
its calculation is to measure that part of the surface which is in
contact with the flame or gases. For example, the heating
surfaces of a boiler tube would be calculated by multiplying the
internal circumference of the tube in feet by its length in feet if
the tube was surrounded by water upon its external surface, and
its internal surface was in contact with hot gases, as is the case
in fire-tube boilers. If this condition is reversed, as is the case
in water-tube boilers, the heating surface would be calculated by
multiplying the external circumference of the tube by its length.

In a horizontal return tubular boiler, the heating surface
is calculated by taking two-thirds of the cylindrical surface
of the shell, adding to this the internal area of all the tubes, plus
two-thirds of the area of both tube sheets and subtracting from
the result twice the combined external cross-sectional area of all
the tubes.

The heating surface of a boiler is proportional to its capacity,
or to the ability of a boiler to evaporate water into steam. The
larger the quantity of water to be evaporated by a boiler, the
larger must be its heating surface.

Staying. — Cylindrical or spherical surfaces retain their shape
when subjected to either a bursting or to a collapsing pressure.

52 STEAM AND GAS POWER ENGINEERING

Surfaces having a flat shape tend to become circular or spherical
when a pressure is exerted. This tendency of flat boiler plates
to distort when pressure is applied is prevented by the use of
stays, as was pointed out in connection with the various types of
boilers. There are many different types of stays; but in general
they consist of small rods which connect the surfaces to be stayed
and transfer the strain either to the shell of the boiler or to some
other surface. These stays are given special names, depending
upon their general construction, their mode of connection, or the
type of surface to which they are best suited.

Settings and Furnaces. — In building a boiler setting the solid
brick wall is preferable to the hollow wall. If the wall is built
in two parts, the space should be filled with ash, crushed brick or
sand, as loose material reduces air leakage by its plasticity.

Proper furnace design will aid in the economical combustion
of coal. The design of a furnace should be modified to suit local
fuels. To burn coals rich in volatile matter, the furnace must be
so designed that the gases given off from the fuel bed remain at a
high temperature until the combustion process is complete.
This means that the combustion chamber for a high volatile
coal must be large enough for the air to mix with the gases given
off from the fuel bed and before such gases come into contact
with the cool heating surfaces of the boiler. This can be accom-
plished by the use of an extension furnace, such as the Dutch
oven type, or by having the heating surfaces elevated at a con-
siderable distance above the grate. The more volatile matter
the coal contains, the greater should be the distance between the
grate and the shell or the tubes of the boiler. The baffling for
water tube boilers should be arranged so that the hot gases from
the fuel bed come first into contact with the baffles at the bottom
of the tubes.

Air infiltration through cracks in boiler setting reduces the
economy of a boiler plant. Visible cracks in the setting should
be covered. The practice of encasing the whole setting in sheet
steel, or the application of asbestos cement on the outside of the
setting, should be employed more generally. Radiation losses
can be reduced by the use of insulating brick.

Sufficient ash pit capacity should be available to handle the
refuse from at least a 12-hour run. In calculating the size of an

BOILERS 53

ash pit, the weight of ashes can be assumed at 40 to 50 pounds
per cubic foot. In plants where the ashes have to be handled
by hand, it is important that the ash pit be so arranged as to
be readily cleaned.

Capacity and Efficiency of Steam Boilers. — Boilers are usually
rated in horsepower. The term horsepower in this connection
is only a matter of convenience, and does not mean the rate of
doing work; boiler horsepower is an arbitrary unit which is applied
to the evaporation of a definite amount of water. The amount of
power developed by a steam power plant per unit weight of steam
generated by the boiler depends upon the engine used. The
American Society of Mechanical Engineers has recommended
that one boiler horsepower should mean the evaporation of 30
pounds of water per hour at 100°F. into steam at 70 pounds gage.
This is equivalent to the evaporation of 34J^ pounds of water per
hour from feed water at 212°F. into dry steam at the same
temperature.

Another method of expressing boiler horsepower is in terms
of heat. To evaporate one pound of water from a temperature
of 212°F. into steam at 212°F. only the latent heat of evapora-
tion at that temperature is required. From the steam tables
page 24, we find that the latent heat of steam at 212°F. is 970.4
B.t.u. The amount of heat required to evaporate 34.5 pounds
from and at 212°F. would be:

34.5 X 970.4 = 33,479 B.t.u.

Thus a boiler horsepower may be stated as the absorption by the
water within the boiler of 33,479 B.t.u. per hour.

As was previously mentioned, the capacity of a boiler depends
upon its heating surface. Boiler manufacturers often rate boilers
in square feet of heating surface. One square foot of boiler
heating surface can evaporate economically 3 to 3.4 pounds of
water, so that a boiler horsepower can be produced by 10 to 12
square feet of boiler heating surface. For fir -tube boilers it is
customary to assume 10 to 12 square feet of heating surface as
representing one boiler horsepower; in water-tube boilers 10 square
feet of heating surface is equivalent to one boiler horsepower.

The following example will illustrate the application of these
terms:

54 STEAM AND GAS POWER ENGINEERING

Example. — A boiler evaporates 4,000 pounds of water per hour into dry
steam The steam pressure is 100 pounds per square inch absolute, and
the feed water enters the boiler at a temperature of 132°F What boiler
horsepower is generated?

Solution. — The heat required to evaporate one pound of the water under
these conditions will be found by reference to the steam tables page 26 to
be

1,186.2 - (132 - 32) = 1,086.2 B.t.u.

The total heat absorbed by the water per hour is

4,000 X 1,086.2 = 4,344.800 B.t.u.
Since 33,479 B.t.u. is the rate of absorption of heat per boiler horsepower,
the power generated by the boiler is

' o An = 129.8 boiler horsepower.

Under good working conditions, a boiler will evaporate 8
to 12 pounds of water per pound of coal, and 11 to 18 pounds of
water per pound of petroleum fuel. The economy of a boiler
plant depends upon the quality of the fuel used, the design of
the furnace and boiler, the condition of setting, and the care in
firing.

The efficiency of a boiler is the ratio of the heat units absorbed
by the steam per pound of fuel fired, to the heat units supplied
by one pound of the fuel. Tests show that the efficiencies of
boilers will vary under ordinary working conditions from about
40 per cent, for small vertical boilers to about 85 per cent, when
well designed boilers are carefully handled. A boiler under aver-
age conditions should show an efficiency of about 70 per cent.
The main losses in a boiler are the heat carried away by the flue
gases, the loss of fuel through grates, the loss due to poor combus-
tion of the fuel, and the heat lost by radiation.

The amount of heat required to produce one pound of steam
depends upon the temperature of the feed water, the steam pres-
sure, and the quality of the steam. In order to compare boilers
working under different conditions, the economy of boilers is
expressed as the equivalent evaporation from and at 212°F.
This means that the actual evaporation per pound of fuel is
reduced to the number of pounds of water which would be evapo-
rated if the feed water had been supplied to the boiler at 212°F.,
and that dry steam was formed at that temperature which is the
boiling point of water at atmospheric pressure.

BOILERS 55

Example. — A boiler generates 9 pounds of steam per pound of fuel from
feed water at 203°F. Calculate the equivalent evaporation from and at
212°F., if the steam pressure is 160 pounds per square inch absolute and the
quality steam 0.98 dry.

Solution. — The heat required to evaporate 9 pounds of feed water at
203°F. into steam which has a pressure of 160 pounds absolute and a quality
0.98 is equal to:

9[335.5 - (203 - 32) + 0.98(858.8)] = 9054.9 B.t.u.
In order to evaporate water at 212°F. into steam at the same
temperature, 970.4 B.t.u. will be required, therefore the equiva-
lent evaporation in accordance with the conditions of the above
problem will be:

9054.9

970.4

= 9.33 lb.

Firing. — To the average person, firing consists merely of open-
ing the furnace door and throwing fuel on the grate. This is,
however, a fallacy. It has been found that some system of firing
must be adopted in order to produce economical combustion of
coal. The method to be adopted depends mainly on the kind of
fuel used.

The spreading method consists of distributing a small charge
of coal in a thin layer over the entire grate. This system of firing
will give satisfactory results with anthracite coal and with some
bituminous coals. With this method, if the fuel is fed in large
quantities and at long intervals, incomplete combustion will
result.

The alternate method consists of covering first one side of the
grate with fresh fuel and then the other. The volatile gases that
pass off from the fresh fuel on one side of the grate are burned with
the hot air coming from the bright side of the fire. This system
is best applied to a boiler with a broad furnace.

The coking method is best adapted for the smoky and for the
caking varieties of bituminous coal. In this method the coal is
put in the front part of the furnace, and allowed to remain there
until the volatile gases are driven off; it is then pushed back and
spread over the hot part of the furnace, and a new charge is thrown
in the front.

Either one of the three systems of firing explained will produce
good results, if properly carried out and if the fire is kept bright

56 STEAM AND GAS POWER ENGINEERING

and clean. Smoke indicates incomplete combustion and with
bituminous coal occurs if the volatile gases are allowed to pass
off unburned.

Management of Boilers. — Before a boiler is started for the
first time, its interior should be carefully cleaned, care being taken
that no oily waste or foreign material is left inside the boiler.
The various manholes and handholes are then closed and the
boiler is filled to about two-thirds of its volume with water.
The fire is started with wood, oily waste, or some other rapidly
burning materials, keeping the damper and ashpit door open.
The fuel bed is then built up slowly.

While getting up the steam pressure, the water gage glass
should be blown out to see that it is not choked, the gage cocks
should be tried, and all auxiliaries such as pumps, injectors,
pressure gages, piping, etc., carefully inspected. The safety
valve should be carefully examined and tried out before cutting
the boiler into service.

When cutting a boiler into service with others, its pressure
should be the same as that of the other boilers. Steam valves
should be opened and closed very slowly in order to prevent
water-hammer and stresses from rapid temperature changes.

During the operation of a steam boiler the safety valve should
be kept in perfect condition and tried daily by allowing the pres-
sure to rise gradually until the valve begins to simmer. Each
boiler should have its own safety valve and under no conditon
should a stop valve be placed between it and the boiler. The
steam gage should be calibrated from time to time with a stand-
ard gage, or still better by means of some form of dead-weight
tester. It is best not to depend on the water gage glass entirely.
Gage cocks are more reliable and should be used for checking the
water level of a boiler.

In case of low water, do not turn on the feed, but shut the
damper, cover the fuel bed with ashes, or if that is not available,
with green coal. The safety valve should not be lifted until the
boiler has cooled down, as an explosion may occur. Also do not
change operating conditions as regards the use of steam. If the
engine is running allow it to continue but do not open valves to
reduce the pressure.

A boiler should be cleaned often and kept free from scale.

BOILERS 57

If water free from impurities is used a boiler may be run several
months without fear of serious scale formation, but in most
places boilers should be cleaned at least once a month. When
preparing to clean a boiler, allow it to cool down, and the water
to remain in the shell until you are ready to commence cleaning.

In emergencies split tubes of fire-tube boilers may be plugged
without throwing the boiler out of service. Also if a tube becomes
leaky in the tube-sheet the fault can be remedied by inserting a
tapering sleeve slightly larger than the inside diameter of the
tube.

A boiler should aways be thoroughly inspected before it is
started. In the case of the locomotive type of boiler the crown
sheet should be given particular attention.

Problems

1. Calculate the heating surface of a fire-tube boiler to which you have
access, after taking the necessary measurements.

2. Calculate the boiler horsepower of the boiler in Problem 1.

3. A boiler plant operating under a pressure of 135 pound per sq. in.
gage generates 18,000 pounds of saturated steam per hour. If the feed
water temperature is 203° F. and the quality of the steam 3 per cent, wet,
calculate the boiler horsepower of the plant.

4. Calculate the approximate heating surface of the boiler plant in Prob-
lem 3, assuming fire-tube boilers.

5. Prove that 34>£ pounds of water per hour from and at 212°F. is the
same as the evaporation of 30 pounds of water per hour from feed water at
100°F. into steam at 70 pounds gage pressure.

6. Compare the equivalent evaporation from and at 212°F. of the follow-
ing boilers:

Boiler A evaporates 1)4 pounds of water per hour from feed water at 140°-
F. and into steam at a pressure of 140 pounds gage, with 2 per cent, priming.

Boiler B evaporates S}4 pounds of water per hour from feed water at
205°F. and into steam at a pressure of 150 pounds gage, with 4 per cent,
priming.

7. Why is a solid wall preferable to a hollow wall for a boiler setting?

8. Why will air infiltration through cracks in a boiler setting interfere
with the economy of a boiler plant?

9. What causes a boiler to explode?

10. Examine some power plant to which you have access and hand in
report showing the following: type of boilers used, steam pressure carried,
methods used for setting boilers (use sketches), and temperature of feed
water; also the relation between the rating of the boilers in horsepower and
the maximum capacity of the power plant in horsepower or kilowatt.

CHAPTER V

BOILER AUXILIARIES

Superheaters

Types of Superheaters. — The boilers considered in the last
chapter have been designed for the generation of saturated
steam. Boilers which are intended for superheated service must
be supplied with superheaters. The installation of a superheater
increases the amount of heat available in the boiler plant and
makes greater economies possible in the utilization of the steam
in steam engines and in steam turbines. Superheated steam
reduces the losses of heat in piping systems, as superheated steam
gives up heat less readily than saturated steam.

The cost of a superheater depends upon the type and size,
as well as upon the degree of superheat maintained. Ordinarily
the installation of a superheater will add about one-third to the
cost of a steam boiler, but the capacity of the boiler plant will
be greatly increased.

Two types of superheaters are used, the independently fired
and the attached type. The independently fired superheater,
as its name indicates, is placed in an independent setting and is
fired by a separate furnace. The attached superheaters are
located directly in the boiler setting, or in the flue leading from
the boiler, derive their heat from the same furnace as the boiler,
and are consequently subject to the fluctuating temperatures of
the furnace. In the independently fired superheater the degree
of superheat is independent of the boiler furnace. By means of
the independently fired superheaters higher temperatures are
possible than with the attached superheaters. The independ-
ently fired superheater is, however, more expensive in first cost,
costs more to operate, and occupies considerable space, as com-
pared with the attached superheater.

Practically all superheaters consist of a series of tubes expanded

BOILER AUXILIARIES

into rectangular steel headers through which the steam from the
boiler passes before entering the piping leading to the engine.
Heat from the furnace gases is thus absorbed by the flowing
steam and its temperature is raised above that at which it left
the boiler.

To prevent a superheater from overheating some provision must
be made to protect it during the firing up of the boiler, or at

Fig. 24. — Babcock and Wilcox superheater.

such other times when the flow of steam through the superheater
is small. This provision has given rise to several designs. Super-
heaters which consist of plain steel tubes in contact with the flue
gases at all times, can be protected by flooding. This is accom-
plished by allowing water to pass through the superheater until the
steam flow is at such a rate as to prevent overheating. Other sup-
erheaters are protected by deflecting the furnace gases by means
of dampers, the flow of gases over the superheating surface being

STEAM AND GAS POWER ENGINEERING

controlled by the operator. In other types, the tubes are pro-
tected by cast iron fins or rings which surround each tube. Cast
iron is capable of withstanding higher temperatures than steel;
by its use the steel tubes are protected and no flooding or other
protective device is necessary.

Babcock & Wilcox Superheater. — Fig. 24 illustrates a Bab-
cock & Wilcox Superheater attached to a boiler of the same type.

Stirling boiler with attached superheater.

The superheater is located directly under the boiler drums be-
tween the first and second pass of the boiler. It consists of a
series of steel tubes expanded into steel headers. The saturated
steam from the boiler drum enters the top header and passes
through the tubes to the bottom header. The superheated steam
is conducted from the bottom header to the main piping.

Stirling Superheater. — Fig. 25 illustrates a Stirling superheater
attached to a Stirling boiler. The arrangement of this boiler

BOILER AUXILIARIES

and superheater, differs from the Stirling boiler for saturated
steam, by the installation of the superheater in place of the mid-
dle bank of tubes. The superheater consists of two drums con-
nected by a series of steel tubes. By the use of diaphragms and
valves located in the two drums the steam makes a circuitous
path through the superheating elements. This superheater is
made of steel tubes which are in the path of the furnace gases,
and are protected from overheating by flooding. The pipe con-
nection for flooding is indicated in the illustration shown.
Heine Superheater. — The Heine superheater, shown in Fig. 26,

Jp-J:L— *

Fig. 26. — Heine superheater.

differs from the types just discussed in that it is not placed
directly in the path of the flue gases, but is located in such a man-
ner that the flow of the flue gases over the superheating surface
may be controlled. This is accomplished by installing the super-
heater at the top of the setting near the side of the steam drum.
The superheater is enclosed in a brick setting which is provided
with two openings. One opening is near the rear of the super-
heater and is connected to the furnace gas chamber by a small
brick flue, which extends downward from the superheater and

STEAM AND GAS POWER ENGINEERING

terminates near the bridge wall. The other opening, which is
provided with a damper, is near the front of the superheater and
connects with the flue gases as they pass from the boiler. The
amount of superheat can be regulated by varying the quantity
of gases passing over the superheating surface. The superheater
consists of a number of U-shaped tubes connected to a steel
header. The header is divided into three compartments.

Foster Superheater. — The Foster
superheater makes use of the special
tube as illustrated in Fig. 27. The
superheater tubes are double and the
outer tubes are protected by cast iron
rings. By the use of an inner and
outer tube, the steam flows against
the heated surface in a thin stream,
thus increasing the effectiveness of the
superheating surface. The cast iron
rings protect the outer tube from
overheating, so that no flooding is
necessary.

The Foster tubes are used in con-
nection with the separately fired types
as well as with the attached types of
superheaters.

Mechanical Stokers

The Field of Mechanical Stokers. —

Greatest fuel economy can be secured
by firing coal frequently and in small
quantities. With hand firing this is
difficult to accomplish and usually
more coal is put into the furnace at
one time than is desirable for eco-
Mechanical stokers make possible the

Fig.

27. — Foster superheater
element.

nomical combustion,
feeding of* small quantities of fuel at regular intervals, the time
between the charges being so regulated that the fuel is completely
burned. When using mechanical stokers the rate of firing is
even, smoke can be greatly reduced, the furnace doors can be kept

BOILER AUXILIARIES 63

closed, and the air supply regulated to suit the fuel and the load.
Low grade fuels which cannot be burned without smoke by hand-
firing methods, are frequently used successfully with certain
types of mechanical stokers.

Mechanical stokers are an absolute necessity in large power
plants on account of the saving in labor. In very small
plants, stokers are not often used on account of the initial high
cost and the expenses in connection with the operation and
upkeep of the stoker mechanism. Stokers are practical in
plants as small as 500-boiler horsepower, if inferior grades of
fuel must be used, the skill of the firemen is low, or smoke must
be kept down to a minimum.

The cost of upkeep is higher for stokers than for hand-fired
furnaces, and is influenced by the size and by the composition of
the fuel used. For best results lumps three inches or smaller
should be used. The initial cost of stoker equipment depends
upon the size and number of stokers installed, the draft available,
and the kind of fuel.

Mechanical stokers are usually classified into three general
types: the chain-grate, the inclined grate, and the underfeed
type. The type of stoker to be selected depends upon the kind
of fuel to be burned.

Chain-grate Stokers. — Fig. 28 illustrates a typical chain-
grate stoker. The entire grate surface is made of a large
number of chain-links, which form the fuel bearing surface.
Sagging of the upper grate surface is prevented by supporting
the weight of the upper grate on small rollers.

Power for driving the stoker is applied at the front. This
causes the top side of the grate to revolve slowly from the front
of the furnace toward the rear. Coal is fed upon the moving
grate through the hopper in the front and is burned as it passes
toward the bridge-wall. Under proper operating conditions,
the speed of the traveling grate is adjusted so that the coal will
have been completely burned to ash when it reaches the end of
the grate and will drop down into the ash pit below. The speed
of the chain grate must be regulated in accordance with the load
on the boiler and the grade of coal used. Care must be taken in
regulating the speed of the grate to prevent loss of fuel to the
ashpit. Leakage of air between the grate and the bridge wall

STEAM AND GAS POWER ENGINEERING

and through the fire bed at the rear must be reduced to a mini-
mum by regulating the depth of the fuel and ash beds.

This type of stoker is usually operated with natural draft.
The entire grate is mounted upon wheels so that it can be re-
moved from the furnace for the purpose of making repairs. A
coking arch of fire brick extends over the top of the grate and
acts as an incandescent surface upon which the volatile gases
strike as they are distilled from the coal. This promotes the
complete combustion of the gases, which, if allowed to strike

Fig. 28. — Chain-grate stoker.

the cooler boiler surface, would be cooled below their ignition
temperature and smoke would result.

The chain-grate stoker is best suited for small sizes of free
burning, non-caking, and high ash bituminous coals. This type
of stoker is not very satisfactory with high-coking, low ash
coals on account of the fusing action of the fuel under the fire
brick arch.

Inclined Grate Stokers. — The Roney stoker, illustrated in
Fig. 29, is representative of the inclined grate over-feed type.
It consists of a hopper for receiving the coal, a series of stepped
inclined grate bars, which extend across the furnace, and a dump-

BOILER AUXILIARIES

ing grate for receiving the ash and clinkers. The grate bars are
T-shaped in section and are pivoted near their lower ends. The
lower ends of the stepped bars rest in slots cut in the rocker bar.
The rocker bar is given a reciprocating motion by a shaft which
passes in front of the stoker and which in turn receives its motion
from the small steam engine. The coal from the hopper at the
front of the stoker first strikes a dead plate, from which it is
pushed on to the inclined grate bars. The grate bars oscillate,
alternately assuming a horizontal and an inclined position, thus

Sectional Throat Piece
(Always specify

of pieces wanted >
Hopper- En d-

boiler Front yT

Stoker Number
Here •
Hopper Shaft ,
Hand Wheel , "

Stud-
Hand Wheel -
Agitator SectorJ

Agitator-^
Sheath-Nut"

Sheath''
Face-Nut -
Lock-Nut-
£ccentric'
Eccentric Strap
Damping Grate Handle'
Connecting Kod
Guard Handle
Guard Handle Catch'
Door Handle

Fig. 29. — Roney stoker.

slowly sliding the coal down the grate. As in the case of the
chain-grate stoker, the rate of feed can be regulated, and when
properly operated the coal should be completely burned when it
reaches the dumping grate. As the fuel passes under the fire
brick arch, the volatile gases are mixed with heated air, the
coal is coked, and smoke is greatly reduced.

The Murphy stoker, illustrated in Fig. 30, is of the inclined
grate, side feed, type. It consists of a Dutch oven, two
coal hoppers, two sets of inclined grates, and a stoking
mechanism. The grate bars are installed so that only alternate

STEAM AND GAS POWER ENGINEERING

ones are movable and these are given a motion which moves
them above and below the stationary bars. This breaks the
adhesion of the coal to the bars and it slowly feeds down the
inclined grates. A toothed clinker bar is placed in the bottom
of the stoker to break up the clinker.

Transverse Section
Fig. 30. — Murphy stoker.

Underfeed Stokers. — Fig. 31 illustrates the Jones underfeed
stoker. It consists of a retort placed inside the furnace and of an
external feeding mechanism. The retort is trough-shaped and
along each side are placed tuyere blocks for admitting the air.
The feeding mechanism is a steam cylinder in which works a
piston. A coal ram is attached to the same piston rod.
As the ram forces coal into the retort, the coal already there is
forced upward. To prevent the coal from heaping up near the
front of the furnace, pusher blocks, connected to the piston rod,
are placed in the bottom of the retort. These tend to maintain a
level fire.

BOILER A UXIL1 ARIES

The operation of this stoker is such that the clinkers and
ash are worked to the top of the fire and are removed from the

31. — Jones stoker,

furnace through the fire doors by hand. The green fuel is fed
below the burning coal, and the hottest part of the furnace is at
the top of the fuel bed. As the burning coal gradually works its

Fig. 32. — Westinghouse Stoker.

way toward the top, any volatile matter is distilled off and is
consumed before reaching the furnace.

Air for the Jones stoker is supplied by a forced draft fan. A
duct from the fan leads the air to the stoker where it passes into

68 STEAM AND GAS POWER ENGINEERING

the furnace through the tuyeres in the retort. This class of
stoker has a high forcing capacity and is suitable for coking
bituminous coals.

In another type of underfeed stoker, the American, the piston
is replaced by a worm, which continuously feeds the coal under-
neath the fire.

Westinghouse Stoker. — The Westinghouse stoker, illustrated
in Fig. 32, combines the principles of the underfeed and of the
inclined grate types of stokers. The fuel from the hopper is fed
into the upper retort, which is located in the bottom of the coal
hopper. A ram in the retort pushes the green fuel outward and
beneath the burning fuel, which rests upon an inclined grate.
The green fuel being introduced under the fire is slowly coked.
The lower ram forces the fuel bed and refuse toward the dump
plates at the rear. The stroke of the lower ram can be regu-
lated to suit the load and the fuel. Air for the combustion of
the fuel is supplied by a forced draft fan, and enters the fuel
bed through openings in the tuyere boxes.

Feed-water Heaters and Economizers

Feed-water Heaters. — If cold water is fed to a boiler, there
will be a difference in temperature at the various parts of the
boiler shell, and strains will be set up by the unequal expansion
and contraction, which will decrease the life of the boiler, be-
sides impairing the tightness of the setting. With hot feed water,
strains due to unequal expansion and contraction are reduced.
Modern power plants are usually provided with feed-water heaters,
which heat the water by exhaust steam. The use of a feed-water
heater will increase the economy of a steam power plant by
utilizing exhaust steam, which would otherwise be wasted.
Under ordinary conditions, heating feed water eleven degrees
will produce about one per cent, gain in economy. The capacity
of a boiler plant can be increased more cheaply by the installa-
tion of a feed-water heater, outside the boiler, than by increas-
ing the size of the boiler. Heating the feed water outside of
the boiler serves also to purify the water before it enters the
boiler.

Feed water can be heated by live steam, by exhaust steam, or
by the waste chimney gases.

BOILER AUXILIARIES

The heating of feed water by live steam is not recommended,
as no use is made of the waste heat.

Feed-water heaters which utilize the heat of exhaust steam
from engines and pumps are most commonly used. Heaters may
be constructed so that the exhaust steam and water come into

Fig. 33. — Open feed water heater.

direct contact and the steam gives up its heat by condensation.
Such heaters are called open feed-water heaters. One type of
open feed-water heater is illustrated in Fig. 33. In this form,
water passes over trays upon which the impurities thrown out
of the water by the heat are deposited, and can be easily removed.
Open feed-water heaters are provided with oil separators through

STEAM AND GAS POWER ENGINEERING

Seamless
Drawn
Brass -

which the exhaust steam passes before entering the heater. Open
feed-water heaters are usually placed on the suction side of the
feed pump and at a higher elevation than the pump cylinders as a
feed pump cannot lift hot water.

If it is desired to pass the water through the heater under pres-
sure or to prevent the steam and water from coming into contact

with each other, some form
of closed heater should be
used. Fig. 34 illustrates a
heater of this type. Here the
steam on one side of the tubes
heats the water on the other.
Such heaters may be con-
structed so that either the
steam or the water flows
through the tubes. Closed
feed-water heaters are more
expensive than the open
types, more difficult to clean,
and are used only in special
cases.

Economizers. — A feed-
water heater which derives its
heat from the flue gases as
they leave the boiler is termed
an economizer. Economizers
increase the capacity of a
boiler plant while providing a
means for storing large quan-
tities of hot water.

Fig. 35 illustrates an econo-
mizer connected to the boiler.
An economizer consists of a series of straight, vertical, cast iron
tubes connected at their top and bottom by headers. The
boiler feed water enters at the end nearest the chimney, passes
through the sections of tubes and is heated by the hot gases
that circulate through them.

The economizer is usually installed in such a manner that the
gases may be by-passed around the tubes or through them. This

'Exhaust

Mud Blow S Settling Chamber
Fig. 34. — Closed feed water heater.

BOILER AUXILIARIES

provision is made to facilitate repairs without shutting down the
boiler.

The tubes of an economizer must be regularly cleaned both
internally and externally. The heating of the water within the
tubes causes impurities to be deposited, which, if allowed to
accumulate, would impair the efficiency of the tubes. Handholes
are placed over each tube to facilitate the cleaning of the internal
surface. The external surface of the tubes must be freed from

Fig. 35. — Economizer.

soot and moisture, which are deposited from the furnace gases.
The cleaning of the external surface of the tubes is accomplished
by a mechanical cleaner. Small cast iron scrapers surround each
tube and are made to slowly travel the length of the tube. In
this manner, any soot deposit which collects upon the surface
of the tube may be removed.

It is not considered good practice to have the temperature of
the water entering the economizer less than 100°F. Low water
temperatures at the inlet to the economizer produce sweating of

72 STEAM AND GAS POWER ENGINEERING

the first rows of tubes, and may result in the corrosion of the
economizer tubes.

An economizer, besides providing a large storage of hot water
for sudden demands, increases the economy of a steam power
plant by utilizing the heat in the flue gases. The reduction of
the flue gas temperature, due to the absorption of heat by the
economizer, may necessitate the addition of mechanical draft
apparatus, or an increase in the height of the chimney. The
purity of the feed water, the sulphur content in the coal, and the
cost of producing additional draft should be considered in
connection with the installation of economizers. With impure
feed water, the cost of keeping the economizer tubes clean may
be excessive.

Draft Producing Equipment

Chimneys. — A chimney or stack is used to carry off the obnox-
ious gases formed during the process of combustion, to discharge
them at such an elevation as will render the gases unobjection-
able, and to create sufficient draft to cause fresh air, carrying
oxygen, to pass through the fuel bed, producing continuous
combustion. The majority of power plants depend upon chim-
neys for draft.

The draft produced by a chimney is due to the fact that the hot
gases inside the chimney are lighter than the outside cold air.
In the boiler plant, the cold air is heated in passing through the
fuel bed, rises through the chimney, and is replaced by cold air
entering under the grate. This means that the amount of draft
produced by a chimney depends upon the flue gas temperature.

The intensity of the draft produced by a chimney depends also
on its height; the taller the chimney, the greater is the draft
produced, since the difference in weight between the column of
the air inside and that of the air outside increases as the height
of the chimney.

The intensity of chimney draft is measured in inches of water,
which means that the draft is strong enough to support a column
of water of the height given. The draft produced by chimneys
is usually one-half to three-fourths of an inch of water.

Chimneys are made of steel, brick, or reinforced concrete.
For small plants steel stacks are most desirable on account of

BOILER AUXILIARIES

lower first cost and ease of construction and erection. Self-
sustaining steel stacks are used in some large power plants
on account of the smaller space required as compared with other
stacks. Steel stacks will rust and
corrode unless they are kept well
painted.

Brick is most commonly used
where permanent chimneys are de-
sired. A brick chimney, unless care-
fully constructed, will allow large
quantities of air to leak in, which will
interfere with the intensity of the
draft. Brick chimneys are built
round, octagonal, or square, and are
usually constructed with two walls
and an air space between them.
The inside wall is lined with fire-
brick. In some cases chimneys are
built of hard burned brick and without
lining. The thickness of the chimney
wall decreases by a series of steps, as
illustrated in Fig. 36.

The use of concrete chimneys,
reinforced with steel rods, is increas-
ing on account of the absence of
joints, light weight, and space eco-
nomy as compared with brick chim-
neys. Ordinarily a reinforced con-
crete chimney is less expensive to
build than a brick chimney.

Draft produced by chimneys is
called natural draft, and varies as the
square root of the height. The ap-
proximate boiler horse-power a chim-
ney will serve can be determined by
the following formula, in which A is
the internal sectional area of the chimney in square feet, and H is
its height above the grate in feet :

Boiler Horsepower = 3.33 (A - 0.6\/A) Via-

Fio. 36. — Brick chimmey.

STEAM AND GAS POWER ENGINEERING

Artificial Draft. — In large power plants equipped with me-
chanical stokers or economizers, the draft produced by chimneys
is insufficient and some artificial method has to be used. A chim-
ney once built is limited in capacity and will seldom be capable
of producing a draft greater than 0.75 inches of water, or about
0.43 ounces pressure. Draft produced by a fan may have a
large range of pressures, depending upon the speed at which it is
operated.

Artificial draft may be produced by steam jets. In some cases
the jets discharge beneath the grates, forcing the air and steam

Fig. 37. — Forced-draft system.

up through the fuel bed. In locomotives the jets of steam from
the engine exhaust are directed upward from the base of the
stack. Steam jets beneath the grates are cheap to install and
with certain varieties of coal are absolutely necessary in order to
prevent the formation of clinkers. Steam jets are uneconomical,
and in stationary practice preference is given to the fan or the
blower systems of artificial draft.

The method by which the fan produces draft gives rise to the
forced and induced draft systems.

In the forced system, Fig. 37, the air delivered to the furnace is
usually taken from the boiler room, and a duct from the fan dis-
charges it into the ash pit. The air is thus forced into the fur-

BOILER AUXILIARIES

nace, which is under a slight pressure. The fact that the pres-
sure within the furnace is greater than that of the atmosphere is
one of the objections to the forced draft system. It may cause
the gas to leak into the boiler room through the cracks in the
setting, and the flames from the furnace to flare out when the fire
doors are opened. To overcome this latter objection, the system

Induced-draft system.

must be equipped with suitable dampers for shutting off the air
when the furnace doors are opened.

The forced draft system lends itself well to old plants, when
the draft produced by chimneys becomes insufficient on account
of increased demands for power. The forced draft system is also
used in connection with the underfeed types of stokers.

In the induced draft system, Fig. 38, the suction side of the fan

76 STEAM AND GAS POWER ENGINEERING

is connected with the breeching of the boiler, and the products
of combustion are discharged through a short chimney. The
breeching is usually provided with a by-pass direct to the stack
to be used in case of accident to the fan. The furnace and ash
pit, in the case of the induced draft system, are under a slight
vacuum, any tendency for air leakage being inward.

Since the induced draft fan handles gases at temperatures of
400 to 500 degrees F., it must be much larger than a forced draft
fan delivering cold air. This means that the cost of the induced
draft system is greater than that of the forced draft system for
the same size power plant.

The induced draft system is generally installed with economi-
zers and is also used extensively in large steam-electric power
plants which have high peak loads.

Mechanical draft permits a higher rate of combustion with
less air per pound of fuel than is possible with natural draft
produced by chimneys. A forced draft system for a large power
plant will cost about one-third that of a brick chimney. In-
duced draft system will cost from 40 to 60 per cent, less than a
brick chimney. To offset the above advantages is the cost of
operating the mechanical draft system. The power required
to operate a fan will amount to from 2 to 5 per cent, of the total
boiler steaming capacity. The mechanical draft systems have
also greater depreciation and maintenance costs than well con-
structed chimneys.

Feed Pumps and Injectors

Water is forced into steam boilers by pumps or injectors. A
pump will handle water at any temperature, while an injector
can be used only when the water is cold. The injector is not as
wasteful of steam as a pump and for feeding cold water has the
additional advantage that it heats the water while feeding it to
the boiler.

Feed Pumps. — Feed pumps may be driven from the cross-head
of an engine. Such pumps are very simple, but can only supply
water to the boiler when the engine is in operation.

Direct acting steam pumps, driven by their own steam cylin-
ders, are most commonly used for feeding stationary boilers, as
they can be operated independently of the main engine and their

BOILER AUXILIARIES

speed can be regulated to suit the feed water demand of the boil-
ers. With a tight suction pipe a direct-acting pump will lift
cold water about 15 feet. Centrifugal pumps are frequently

Fig. 39. — Boiler feed pumps.

used in large power plants and are generally driven by steam
turbines.

The details of construction of two forms of direct-acting pumps

STEAM AND GAS POWER ENGINEERING

are shown in Fig. 39. The essential difference between these
pumps is that one uses a piston and the other a plunger. Both
types are extensively used. The piston pattern occupies less
floor space, but is more difficult to pack.

In the pump shown in Fig. 39, 1 is the steam cylinder and 2 is
the water cylinder. The valve E is moved by the vibrating arm
F, and admits steam into the cylinder, 1. If steam is admitted
at the left of the piston A, the piston will be moved to the right,

Fig. 40. — Boiler feed pump.

pushing the plunger B, driving the water through the valve K}
and into the feed line at 0. While the plunger is moving to the
right, a partial vacuum is formed at its left which action opens
the valve N and draws the water from the supply at C. When
the plunger B reaches the extreme position to the right, the vibrat-
ing arm F moves the valve E to the left, admitting steam which
pushes the piston and plunger to the left, driving the water
through the valve L and taking a new supply through M . The
function of the air chamber P is to secure a steady flow of water

BOILER AUXILIARIES

through the discharge and to prevent excessive pounding at
high speeds by providing a cushion for the water.

The pump shown in Fig. 40 differs from the one just described
in that the steam valve G is operated by the steam in the steam
chest and not by a vibrating arm outside of the cylinder. The
piston C is driven by steam admitted under the slide valve G,
this valve being moved by a plunger F. This plunger F is
hollow at the ends and the space between it and the head of the
steam chest is filled with steam. Thus the plunger remains
motionless until the piston C strikes one of the valves I, exhausting
the steam through the port E at one end. The water end is
similar to that of the pump in Fig. 39.

Injectors. — Injectors are used very commonly for the feeding
of locomotive, portable, and small stationary boilers. In some
power plants injectors are used in conjunction with pumps as an
auxiliary method of feeding boilers.

Steam

Fig. 41. — Injector.

The general construction of an injector is illustrated in Fig.
41. Steam from the boiler enters the injector nozzle at A,
flows through the combining tube BC, and out to the atmosphere
through the check valve E and overflow. The steam in
expanding through the nozzle A attains considerable velocity,
and forms sufficient vacuum to cause the water to rise to the
injector. The steam jet at a high velocity coming into contact
with the water is condensed, gives up its heat to the water, and
imparts a momentum which is great enough to force the water

STEAM AND GAS POWER ENGINEERING

into the boiler against a steam pressure equal to or greater
than that of the steam entering the injector.

As soon as a vacuum is established in the injector and the water
begins to be delivered to the boiler, the check valve E at the over-
flow closes. Should the flow of feed water to the boiler be inter-
rupted, due to air leaking into the injector or to some other cause,
the overflow will open and the steam will escape to the atmos-
phere.

Due to the fact that the vacuum in an injector is broken as
the temperature of the water increases, injectors can work only
when the feed water is 150°F. or cooler.

Duty of Pumps. — The duty of a pump is measured in foot
pounds of work done in moving water for each 1,000 pounds of
steam used, or for each million British thermal units delivered in
the steam.
Duty per million B.t.u. is:

Water horsepower X 1,980,000 X 1,000,000.
B.t.u. in steam used per hour

Small direct-acting pumps have duties as low as 15,000 foot
pounds per 1,000 pounds of steam used. Large pumping engines
have shown results as high as 181,000,000 foot pounds per 1,000
pounds of steam.

Grates for Boiler Furnaces

Grates are formed of cast iron bars. Several forms of grate
bars are illustrated in Figs. 42 and 43. Plain grates (6), Fig.

Fig. 42. — Grate bars.

42, are best adapted for caking coals and are usually provided
with iron bars, cast in pairs, and with lugs at the side. The
Tupper type of grate (c) Fig. 42, is more suitable for the burning
of hard coal, which does not cake. The grates of a boiler furnace

BOILER AUXILIARIES 81

can be easily inter-changed to suit the fuel burned. For most
economical results some form of rocking and dumping grate, as
shown in Fig. 43, should be used.

Fig. 43. — Dumping grate.

Coal and Ash Handling Systems

In small power plants the coal is delivered to the furnace and
the refuse is removed from the ash pit by hand shoveling. In
such cases the coal pockets or coal bunkers should be located
opposite the boilers, so that the rehandling of coal is reduced to
a minimum. If the coal cannot be stored in front of the boilers,
coal tip-carts are found very satisfactory for conveying the fuel
to the boiler room.

As plants increase in size, mechanical coal and ash handling
systems are warranted. The coal handling system usually
consists of the following equipment: a receiving hopper, into
which the coal is delivered; a crusher, which reduces the fuel to
such a size as can conveniently be handled by stokers; elevating
and conveying systems for raising the coal from the crusher
and for distributing it to the bunkers, which are placed over the
boilers; and spouts which deliver the fuel from the bunkers to the
stokers.

The endless chain bucket conveyor is frequently used for
handling both coal and ashes. This system consists of a con-
tinuous series of buckets suspended between two endless chains.
The discharge of the coal from the buckets into the bunkers over
the boilers is effected by a tripping device which turns the buckets
over. The buckets pass beneath ash hoppers under the boilers.
The ashes are elevated by the buckets and discharged into an
ash storage bin. Hoist and trolley systems, scraper conveyors,
screw conveyors, and belt conveyors are also used in handling

82 STEAM AND GAS POWER ENGINEERING

coal and ashes. Vacuum or steam conveyors are used for han-
dling ashes and fine coal. Vacuum and steam conveying systems
consist of a pipe line through which the ashes or fine coal are
carried by air or steam at high velocity.

Problems

1. Discuss the advantages of superheaters for large power plants.

2. Report on the uses of mechanical stokers in the power plants in your
vicinity.

3. Give complete directions for the handling of an underfeed mechanical
stoker.

4. Calculate the per cent, gain which will result from preheating feed water
to 200° F., from a temperature of 70°F., if a boiler plant is operated at a
steam pressure of 140 pound gage.

5. Examine the draft producing systems in the power plants in your vicin-
ity, and hand in a complete report, showing types of stacks, mechanical
draft systems, and the intensity of the draft used.

6. A pumping engine pumps 8,000,000 gallon of water per day of twenty-
four hours, against a head of 110 feet. It uses 2,500 pounds of steam per
hour. If the steam pressure is 140 pounds per square inch gage, and the
feed water temperature is 202°F., calculate the duty of the pumping engine
per million B.t.u.

CHAPTER VI
PIPING AND BOILER ROOM ACCESSORIES

Grades and Sizes of Piping. — Piping used to convey the steam
generated in a boiler is made of wrought iron or of mild steel.
Wrought iron pipe is superior to steel pipe, as it is softer, is
easier to thread, and is not subject to corrosion. Wrought
iron pipe is more expensive and more difficult to secure than
steel pipe. The largest portion of piping used in power plants is
of mild steel, lap or butt welded for high pressures. Cast steel
pipe has been found more suitable for superheated steam than
mild steel pipe.

Sizes of standard steam pipe up to 12 inches are named by
their inside diameter; above 12 inches they are designated
by their outside diameter. The sizes of boiler tubes are given by
their outside diameter.

Standard steam pipe is made in sizes of }i, }>i, %, %, Y±, 1,
1H, IK, 2, 2K, 3, 3}i, 4, 4^, 5, 6, 7, 8, 9, 10, 11, and 12 inches.
Standard pipe is suitable for pressures up to 125 pounds per
square inch.

The various grades of pipe are: standard, extra heavy, and
double extra heavy. Extra heavy and double extra heavy have
the same outside diameter as standard pipe, but the inside
diameters are smaller, due to the greater thickness of the pipe.
Extra heavy pipe is suitable for pressures up to 250 pounds per
square inch, while double extra heavy pipe can be used for
pressures up to about 1,000 pounds per square inch.

Pipe Fittings. — Two kinds of fittings are used in steam power
plants, the screwed and the flanged fittings. For saturated steam
and for pressures less than 150 pounds, all fittings 3 3^ inches and
under may be screwed. Fittings 4 inches and over should have
flanged ends. Screwed fittings, when properly installed, are
less liable to leak than flanged fittings, which are put together
with gaskets. Flanged fittings are easily taken apart and are
most generally used in modern power plants.

84 STEAM AND GAS POWER ENGINEERING

The pipe fittings most commonly used are illustrated in Figs.
44 to 52.

Fig. 44. — Pipe unions and couplings.

Fig. 45.— Ells.

Fig. 46.— Reducing ell. Fig. 47. — Tees.

Fig. 48.— Cross. Fig. 49.— Bush- Fig. 5 0. — Re-

ing.

ducer.

Fig. 51. — Cap. Fig. 52. — Plug.

Fig. 44 illustrates several forms of pipe unions and couplings,
which are used for uniting two lengths of pipe.

PIPING AND BOILER ROOM ACCESSORIES 85

The elbow or ell shown in Fig. 45 is employed for connecting
two pipes, of the same size, at an angle to each other. If the pipes
are of different diameters a reducing ell, as shown in Fig. 46,
should be used.

The tee shown in Fig. 47 is used for making a branch at right
angles to a pipe line.

The cross shown in Fig. 48 is used when two branches must be
connected in opposite directions.

In order to reduce the size of a pipe line, a bushing, Fig. 49,
or a reducer, Fig. 50, can be used.

To close the end of a pipe, a cap, Fig. 51, is used, while the
plug shown in Fig. 52, is used to close a fitting threaded on the
inside.

In cast iron flanged fittings the flange is always a part of the
casting. For joining two ends of a pipe, the pipe and flange
are threaded, the pipe is screwed beyond the face of the flange,
and the two are faced off together. Another method is to weld
the flanges on the pipe.

Expansion of Piping. — In piping systems, provision must be
made to allow for the expansion and contraction due to variation

in the temperature of the steam within
the pipe. Unless a pipe expands freely,
distortion or injurious strains on the
joints and fittings will occur.

The simplest method is to permit the

Fig. 53. — Double-swing ex-
pansion joint.

Fig. 54. — Long radius bends.

expansion to adjust itself in a threaded joint. Such an arrange-
ment is shown in Fig. 53. Any expansion or contraction in the
piping is adjusted by a slight movement in the screwed joints.

Another method quite extensively used in high pressure
piping is to insert a long radius bend, as illustrated in Fig. 54.
A long radius bend, besides taking care of the expansion after

STEAM AND GAS POWER ENGINEERING

the piping is in place, reduces the number of joints, decreases
friction, and is much easier to erect than pipe fittings. One of
the objections against the use of long radius bends is the space
required.

The slip expansion joint illustrated in Fig. 55 overcomes the
above objection. The main casting of this expansion joint is
divided into two parts. The expansion or moving element
consists of a non-corrodible bronze sleeve, made steam tight
by the long stuffing box. The sleeve is supported at the outer
end by flanges. In installing a slip expansion joint, the pipe
must be securely anchored to prevent the steam pressure from
forcing the joint apart.

.Olanol Bolts

Tzzzzzzzzzzzz.

TZZZZZZZZZZZj

L i'm if Roofs

Guide-

"Body
Fig. 55. — Expansion joint.

Pipe Covering. — All pipes carrying steam and hot water should
be covered with some heat insulating material in order to reduce
the loss of heat to a minimum. If saturated steam, is conveyed
in uncovered steam pipes, some of it will condense, reducing the
economy of the plant. Tests demonstrate that pipe covering
will pay for itself in a very short time.

Pipe covering is usually applied in sections, molded to the re-
quired size of the pipe and secured to the pipe by bands. Valves
and fittings are usually covered with a plastic insulating mortar.

Erecting Pipe. — Steam pipe lines should always be laid with a
gradual slope in the direction in which the steam flows. This will
allow the condensation and the steam to flow in the same direc-
tion. If this is not done water may accumulate, will be picked

PIPING AND BOILER ROOM ACCESSORIES 87

up by the steam, and may cause much damage either to the fit-
tings or to the engine.

Care must be taken that the pipe lines have the proper align-
ment in order to prevent strain on the fittings. Pipe lines must
be supported by wall brackets, hangers, or floor stands to guard
against excessive deflection and vibration.

Valves. — The function of a valve is to control and regulate
the flow of water, steam, or gas in a pipe. In the globe valve,
Fig. 56, the fluid usually enters at the right, passes under the

jp^*

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1111 JUIUII

r-vJl^1

Fig. 56. — Globe valve.

Fig. 57. — Gate valve.

valve, and out at the left. This method of installation permits
the valve stem to be packed, when the valve is closed, without
cutting the steam pressure off the entire line.

If a globe valve is installed so that the fluid enters at the left.
Fig. 56, the pressure of the steam, when the valve is closed, tends
to keep it in that position and there is much less likelihood of the
valve leaking, but the valve cannot be opened if it should be-
come detached from the stem.

Globe valves in sizes up to three inches have brass bodies; large
valves are made of cast iron for ordinary pressures and tempera-
tures, and of cast steel for high temperatures and pressures.

A gate valve is shown in Fig. 57. This form of valve gives a
straight passage through the valve, and is preferable for most
purposes to the globe valve. For high pressure work and in

STEAM AND GAS POWER ENGINEERING

large sizes, gate valves are usually of the outside screw type, which
means that the stem protrudes beyond the hand wheel. This
enables the operator to tell at a glance whether the valve is open
or closed. The gate valve illustrated in Fig. 57 is of the inside
screw type, and is used in small sizes and also in plants where the
screw must be protected from dirt.

Fig. 58 illustrates an angle valve which takes the place of an
ordinary valve and ell.

The function of a check valve, illustrated in Fig. 59, is to allow
water or steam to pass in one direction but
not in the other. A boiler feed line should
always be provided with a check valve and
also with some form of globe or gate valve to
enable the operator to examine and repair the
check valve.

Fia. 58. — Angle valve.

Fig. 59. — Check valve.

Blow-off Valves. — A boiler should always be provided with a
blow-off connection at its lowest point for removing mud and
sediment, as well as for the purpose of draining the boiler. The
blow-off connections must be provided with blow-off valves,
which can be easily opened, which will give a free passage for scale
and sediment when open, and which will not leak when closed.
Best practice recommends the use of two valves or of a valve and
a blow-off cock in the blow-off line of each boiler.

Safety Valves. — The function of a safety valve is to prevent
the steam pressure from rising to a dangerous point. The two
common forms of safety valves are : the lever safety valve and
the spring or pop safety valve.

The lever safety valve shown in Fig. 60 consists of a valve disc
which is held down on the valve seat by means of a weight acting
through a lever, the steam pressing against the bottom of the disc.

PIPING AND BOILER ROOM ACCESSORIES 89

The lever is pivoted at one end to the valve casing, and is marked
at a number of points with the pressures at which the boiler will
blow off if the weight is placed at that particular point. Lever
safety valves are seldom used in modern power plants.

Fig. 60. — Lever safety valve.

Fig. 61. — Pop safety valve.

The pop safety valve shown in Fig. 61 differs from the lever
valve in that the valve disc is held on its seat and the steam
pressure is resisted by a spring, in place of a weight and levers
Pop safety valves can be adjusted to blow off at various pressure,
by tightening or loosening the spring pressure on the valve disc.

Fig. 62. — Steam gages.

The American Society of Mechanical Engineers recom-
mends that two or more safety valves be installed on every
boiler, except in the case of small boilers which require a safety
valve 3 inches or smaller.

Steam Gages. — A steam gage indicates the pressure of the
steam in a boiler. The most common form, shown in Fig. 62,

STEAM AND GAS POWER ENGINEERING

consists of a curved spring tube closed at one end. One end of
the tube is free, while the other is fastened to the fitting which
is secured into the space where the pressure is to be measured.
The cross section of the tube is made elliptical or irregular in
shape so that pressure applied to the inside of the tube causes
the free end to move. This motion is communicated by means
of levers and small gears to the needle which moves over a
graduated dial face, and records the pressure directly in pounds
per square inch.

Water Glass and Gage Cocks. — The height of the water level
in a boiler is indicated by a water glass, one end of which is
connected to the steam space and the other end to the water
space in the boiler. All boilers should also be provided with three

gage cocks, one of which is set at the
desired water level, one above it and
one below. These are more reliable
than the water glass and should be used
for checking the glass.

Water Column. — The steam gage,
water glass, and gage cocks are usually
fastened to a casting called a water
column. One form of water column is
shown in Fig. 63. This water column
is fitted with a float and a whistle to
notify the operator should the water in
the boiler become too low or too high.
An operator who takes proper care of
the boilers in his charge will never
allow the water to be at a height that
will necessitate audible warnings.
Steam Traps. — The object of a steam
trap is to drain the water from pipe lines without allowing the
steam to escape. One form of steam trap is shown in Fig. 64;
in this case the valve is controlled by a float when the water in
the trap rises to a sufficient height. In another type of trap,
called the bucket type, there is a bucket in the interior of the
trap, which when filled with the condensed steam operates as a
float and opens a valve.

Water column.

PIPING AND BOILER ROOM ACCESSORIES 91

Traps which receive the condensed steam and return it to the
boiler are called return traps.

Fig. 64. — Steam trap.

Fusible Plugs. — Plugs with a core of some fusible metal are
used to protect boilers from overheating. If a plate, into which
a fusible plug is screwed, becomes overheated, the fusible metal
melts and runs out allowing the steam and hot water to run in-
to the boiler furnace.

Fusible plugs are placed about three inches above the top row
of tubes in a cylindrical tubular boiler and in the lower side of
the upper drum of a water tube boiler.

Problems

1. Make a clear sketch showing the location of the boiler stop valve with
reference to the piping from the boiler.

2. Make an inspection of some plant in your vicinity and report on the
following :

(a) Types of fittings used.

(6) Are the steam pipes covered? If so, with what material.

3. Make a clear sketch showing how you would arrange the piping and
fittings in connection with a boiler blow-off connection.

4. Where should safety valves be placed on fire tube boilers? On water
tube boilers?

6. Sketch three (3) forms of pipe supports.

6. Why place a fusible plug about three inches above the top row of tubes
in a cylindrical tubular boiler?

CHAPTER VII
STEAM ENGINES

Description of the Steam Engine. — A steam engine is a motor
which utilizes the energy of steam. It consists essentially of a
piston and cylinder with valves to admit and to exhaust the steam,
a governor for regulating the speed, some lubricating system for
reducing friction, and stuffing boxes for preventing steam leakage.

In the steam engine working as a motor, continuous rotary
motion of the shaft is essential. This is accomplished by the inter-
position of a mechanism consisting of a connecting rod and crank,
which changes the to-and-fro, or reciprocating motion, of the
piston into mechanical rotation at the shaft. A steam engine in
which the reciprocating motion of the piston is changed into
rotary motion at the crank is called a reciprocating steam engine
to differentiate it from the steam turbine to be described in a
later chapter.

The various parts of a steam engine are illustrated in Figs.
65, 66 and 67.

Steam from the boiler at high pressure enters the steam chest
A, Fig. 65, and is admitted alternately through the ports BB
to either end of the cylinder by the valve C. The same valve also
releases and exhausts the steam used in pushing the piston D.
E is the cylinder in which the steam is expanded. The motion of
the piston D, Fig. 66, is transmitted through the piston rod F
to the crosshead G, and through the connecting rod H to the
crank I, which is keyed to the shaft K.

The shaft is connected directly, or by means of intermediate
connectors, such as belts or chains, to the machines to be driven.

The shaft carries the flywheel L (Fig. 66), the function of which
is to make the rate of rotation as uniform as possible and to carry
the engine over the dead-centers. The dead-center occurs when
the crank and connecting rod are in a straight line at either end of
the stroke, at which time the steam acting on the piston will not

STEAM ENGINES

turn the crank. A flywheel is sometimes used as a driving pulley,
as shown in Fig. 67.

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Fig. 65. — Engine cylinder and steam chest.

The eccentric shown in Fig. 67 also rotates with the shaft, and
its function is to impart a reciprocating motion to the valve. The
eccentric consists of a circular iron disk, so keyed to the shaft

Fig. 66. — Steam engine.

that its center is eccentric to the center of the shaft. Around
the eccentric fits a ring,- called the eccentric strap. The eccen-
tric strap is bolted to a rod, called the eccentric rod. The eccen-

STEAM AND GAS POWER ENGINEERING

trie imparts a backward and forward motion to the valve through
the eccentric rod and valve stem. This motion given to the valve
is dependent upon the eccentricity of the eccentric. The eccen-
tricity is the distance between the center of the eccentric and the
center of the shaft. Changing the eccentricity changes the travel
of the valve. The travel of the valve, or the total distance it moves,
is equal to the throw of the eccentric, or to twice the eccentricity.

Top Cylinder-^^i
Heat, '

Cylinder ~>\
Lacjo/incf

Bo-Hvm Cylinder^
Head

Cross- Head- .
Oiler Bracket

Valve Stem Driver
Valve Stem Square

Drivinq
Pultef

Fig. 67. — Vertical steam engine.

Stuffing boxes which prevent the escape of steam around the
rods are illustrated at M and N in Figs. 65 and 66 respectively.

Early History of the Steam Engine. — The use of steam for the
pumping of water dates back to about 1700. The operation of
the engines of that time differed from the modern steam engine
in that steam was admitted into a closed vessel, at atmospheric
pressure, and was condensed by throwing cold water over the
external surface of that vessel. The vacuum thus created was
utilized in the production of work.

STEAM ENGINES 95

The Newcomen engine of 1705 first made use of a cylinder and
piston, but worked on the same principle as the engines mentioned
above.

In 1712 Newcomen designed a steam engine in which the con-
densation of the steam was affected by introducing water into the
cylinder. The operation of the valves in the Newcomen engine
was by hand and steam at only atmospheric pressure was utilized.

In 1718 Henry Brighton invented a self-acting machine. The
valves consisted of a series of tappets operated by the beam
of the engine.

James Watt in 1769 laid the foundation for the modern steam
engine. His greatest improvements consisted in transferring
the steam to another vessel for condensation, making use of pres-
sure greater than atmospheric, constructing the steam engine
double-acting, and in inventing the steam engine indicator.
Watt was the first to realize the advantages resulting from using
steam expansively, although this was applied to an actual engine
by Wolfe in 1804. ■

Losses in Steam Engines. — The main losses in a steam engine
are:

1. Loss in pressure as the steam is transferred from the steam
boiler to the engine cylinder, due to the throttling action in the
steam pipe and ports. Steam in passing through a small port loses
part of its energy in overcoming friction. To reduce such losses
to a minimum, the pipes and ports must be ample and all steam
passages must be as straight as possible.

2. Leakage past piston and valves. The losses due to leakage
past the piston and valves are usually very small in well designed
engines and may be kept so by proper attention. .

3. Loss due to the condensation of the steam in the cylinder.
This loss takes place when the entering steam comes in contact
with the cylinder walls, which have been cooled by the exhaust
steam which previously filled the cylinder. Cylinder conden-
sation becomes greater as the difference between the admission
and exhaust pressures is increased. When steam is sufficiently
superheated, no condensation takes place, but the loss, though
somewhat lessened, is still present.

Losses due to condensation of steam within the cylinder can
also be decreased by increasing the engine speed, by regulating

STEAM AND GAS POWER ENGINEERING

the point of cut-off, by compounding, using steam jackets, increas-
ing the size of the units, or by employing the uniflow principle,
to be described later.

4. Radiation losses. Radiation losses take place when the
steam passes through the steam pipes from the boiler to the
cylinder and also while the steam is in the cylinder. Radiation
losses in the steam pipes leading from the boiler to the engines
can be reduced by the use of a good pipe covering. The radia-
tion losses from the cylinder of the engine are reduced by jack-
eting the cylinder with some non-conducting material.

Fig. 68.— Engine cylinder and plain slide valve.

5. Losses of heat in the exhaust steam. Seventy-five per
cent, or more .of the heat available in the steam when it enters
the engine cylinder is carried away in the exhaust. Part of this
heat can be recovered by using the exhaust steam for the heating
of feed water before it enters the boiler, for the heating of build-
ings, or in employing the exhaust steam in connection with
various manufacturing processes.

6. Mechanical losses due to the friction of the moving parts.
These losses may be kept at a minimum by proper lubrication.

Action of the Plain Slide Valve. — Fig. 68 shows a section
through a steam engine cylinder with the slide valve in mid-posi-
tion. A and B are the steam ports, which lead to the two ends of

STEAM ENGINES

the cylinder; C is the exhaust space. The steam ports are sepa-
rated from the exhaust space by the two bridges, D and E. F is
the steam chest. V is a plain slide valve, commonly called a D
slide valve. The amount S that the valve V extends over the
outside edge of the port, when the valve is at the center of its
travel, is called the steam lap. Similarly the amount X by which
the valve over laps the inside edge of the port when it is in mid-
position is called the exhaust lap. M and N are the steam and
exhaust pipes respectively.

A term frequently used in connection with the operation of
valves is "lead." By lead is meant the amount that the port is
uncovered when the engine is on either dead-center. The object
of lead is to supply full pressure steam to the piston as soon as it
passes the dead-center.

Fig. 69. — Admission.

Fig. 70.— Cut-off.

The motion of the valve produces four events: admission,
cut-off, release, and compression. Admission is that point at
which the valve is just beginning to uncover the port. The
position of the valve for this event is shown in Fig. 69. Cut-
off occurs, Fig. 70, when the valve covers the port, preventing

Fig. 71. — Release.

Fig. 72. — Compression.

further admissioi) of steam. This is followed by the expansion
of the steam until the cylinder is communicated with the exhaust
opening, at which time release, as shown by Fig. 71, occurs.
Compression occurs when communication between the cylinder
and exhaust opening is interrupted, Fig. 72, and the steam remain-
ing in the cylinder is slightly compressed by the piston. The
valve is in the same position at cut-off as it is at admission, only

98 STEAM AND GAS POWER ENGINEERING

y////////////c

it is traveling in the opposite direction. Similarly the positions
of the valve are the same at release and compression.

Types of Plain Slide Valves. — If the valve is constructed
without laps, as shown in Fig. 73, there is no period of valve
closure, and the steam acts non-expansively. The release and
the cut-off of the steam occur at practically the same instant.
The steam admission in one end of the cylinder takes place
throughout the entire stroke, while the steam in the opposite
end of the cylinder is exhausted at the same time. Such a valve

would be uneconomical because of its
failure to provide for the expansion of
, the steam, and as a result is only re-
\ sorted to in the direct-acting steam

FiG.TS.-Valvewithoutlaps. PumP' which is essentially a special

case. For best economy a steam engine
should be provided with a valve which cuts off the steam at
about one-third of the stroke and releases it somewhere near
the end of the stroke.

The simplest type of valve for steam engines is the plain slide
valve, illustrated in Fig. 68. This type of valve is not used where
steam economy has to be considered. The plain slide valve is used
to a limited extent in connection with portable engines, traction
engines, or small stationary steam engines. The chief ob j ection to
its use on engines of larger sizes is that it is not balanced. If the
difference between the steam and the exhaust pressures is large,
the force of the steam holding the valve upon its seat is also
large, and consequently the force required to move the valve
backward and forward may be excessive. This consumes a part
of the work developed by the engine, needlessly strains the valve-
gear, and makes it difficult to keep the valve steam-tight The
objections to the plain slide valve are remedied by the use of
balanced valves.

Balanced Valves. — The piston valve, illustrated in Fig. 65,
is one form of balanced valve. The pressures upon all sides that
would force the valve against its seat are balanced by equal
and opposite forces. When well made, and properly fitted with
packing rings, little leakage occurs, but small piston valves are
often made without packing rings and in such a case leakage is
very likely to occur.

> STEAM ENGINES 99

The balancing of the flat slide valve is accomplished by the addi-
tion of balancing plates. Such a device is shown in Fig. 74. It
consists of a machined plate, arranged so that it excludes the high
pressure steam from the top of the valve. This eliminates the
pressure that would force the valve upon its seat, and the only
friction theoretically present is that due to the weight of the
valve itself. Various valves employing this principle have been
devised. Some are only partially balanced. Others differ in the

,Balance Plate

Steam. .Chest ©over

Piston'
Fig. 74. — Balanced valve.

method of maintaining a steam tight joint between the valve and
the balancing plate. The principle involved in all balanced
valves is the same.

The Double Ported Valve. — One difficulty in the use of the
plain slide valve is that a large movement or travel of the valve
is necessary in order to fully open the port. This makes it
difficult to use the plain slide valve in engines having a large
diameter and short stroke. The double ported valve, Fig. 75,
overcomes this difficulty. Instead of using one large port for the

100 STEAM AND GAS POWER ENGINEERING

passage of the steam, two ports, whose combined areas would
equal that of a single port, are used.

Fig. 75. — Double ported valve.

The Corliss Engine. — The slide valve engine requires long
ports or passages for the steam. This increases the amount of
surface to which the steam is exposed. Another fault of the
slide valve is that the same port is used for the live steam enter-

Fig. 76. — Corliss engine cylinder and valve gear.

ing the cylinder, after it has been cooled by the exhaust steam.
To overcome these objections four-valve engines have been in-
troduced. One of the earliest and best of these types is the Corliss
engine.

STEAM ENGINES 101

The cylinder of a Corliss engine is illustrated in Fig. 76. It
includes four valves, two for the control of the entering steam and
two for the exhaust. The valves are cylindrical in shape and are
located at the top and bottom of the cylinder at the extreme ends
of the stroke of the engine. The steam and exhaust valves oper-
ate respectively in the chambers S and E. The bell crank levers
D work loosely on the valve stems; they are connected to the wrist
plate B by the rods K. The steam valve levers M are keyed to
the valve stem J, and are also connected by the rods 0 to the
dash pots P. The bell crank levers D carry at their outer ends
V-shaped steam hooks F} which are provided with steel catch
plates that engage with the arms M . The levers G are connected
by the rods H to the governor, and carry upon their outer facas
small cams which release the steam hooks. The exhaust valve
levers N are connected directly through the rods L to the wrist
plate; their motion being identical with that of a plain slide
valve.

In the operation of the engine, the wrist plate is given an oscil-
lating motion by the eccentric to which it is connected through the
rod A. This causes the bell crank lever D to oscillate upward
and downward about the spindle J as an axis. Upon the ex-
treme downward movement, the steam hook engages the main
valve lever M, and the upward movement of the hook lifts the
lever M and opens the valve. The opening of the valve continues
until the hook is disengaged by coming in contact with the knock-
off cam on lever D. The instant the valve is released, the vacuum
created in the dash pot P causes the quick return of the valve to
its normal position. The governor controls the position of the
knock-off cam, thus regulating, the cut-off by varying the point
at which the valve is released.

The trip gear described becomes impractical when the speed of
the engine is high. Consequently most Corliss engines, with the
trip or releasing valve gears operate at low speeds, usually about
85 to 100 revolutions per minute.

Poppet Valves. — Superheated steam decreases cylinder con-
densation and increases the economy of the steam engine, but
highly superheated steam causes slide valves and those of the
Corliss type to warp. To overcome this objectionable feature,
and at the same time to take advantage of the gain that may be

102 STEAM AND GAS POWER ENGINEERING

derived from superheated steam, the poppet valve engine was
designed.

Details of one type of poppet valve engine are shown in Fig.
77. The cylinder has four double-seat poppet valves, two are
used for regulating the inlet steam and two for regulating the
exhaust. The operation of the valves is accomplished by the
movement of an eccentric acting through a series of levers. The
eccentric is attached to a lay shaft, which runs longitudinally
along the outside of the cylinder and is finally geared to the main
shaft.

The Uniflow Steam Engine. — The reciprocating steam engines
previously described are of the counter-flow or double-flow
type. The steam, after its expansion in this type of engine, is
reversed in its. course, the cylinder walls are subjected to the
cooling action of the exhaust steam during the entire exhaust
stroke, and the economy of the engine is greatly decreased by the
losses due to the condensation and re-evaporation of the steam.
The uniflow engine, Fig. 78, has been designed to decrease the
above mentioned losses. In the uniflow engine the steam enters
at the ends of the cylinder as in the counter-flow engine, but is
exhausted through special ports arranged around the center of
the cylinder at the farthest point from the heads. The piston
acts as an exhaust valve uncovering and covering the exhaust
ports. The cylinder heads are exposed to the temperature of
the exhaust steam for a very short time. The steam caught in
the clearance space is compressed against the cylinder heads,
which are jacketed with live steam. The incoming steam is not
chilled by coming in contact with cool surfaces, and the losses
due to cylinder condensation are greatly decreased.

The single cylinder uniflow engine running condensing is
nearly as economical as a compound engine of the counter-flow
type. The uniflow engine has also shown remarkable economy
at light loads.

Reversing Engines. — Locomotives, marine engines, hoisting,
and other reversing engines must be provided with a valve gear
by which the direction of rotation may be reversed. The
Stephenson link motion and the Walschaert radial valve gear
are the two types most commonly used.

The Stephenson link motion is illustrated in Fig. 79. This

STEAM ENGINES

103

104 STEAM AND GAS POWER ENGINEERING

STEAM ENGINES 105

motion makes use of two eccentrics A and B. Eccentric A
produces rotation of the engine in one direction and is called the
forward eccentric; eccentric B causes rotation in the opposite
direction. Attached to each eccentric is an eccentric rod R,
which connects to one end of the slotted link L. The link L is
connected to the reversing lever so that its position may be
varied at will. The valve stem is attached to the link block in
such a manner that the link is free to move. Raising or lower-

>£ Lever

Fig. 79. — Stephenson link motion.

ing the link by the reversing lever simply changes the position of
the link with reference to the link block and the valve.

In the position shown, the valve is controlled by the forward
eccentric A. To reverse the direction of rotation, the link L
must be raised until the eccentric rod of the backing eccentric
B is directly in line with the valve stem. The valve motion
would then be controlled by the backing eccentric, and
the engine shaft would rotate in the opposite direction.

If the link is raised until the valve stem is midway between the

106 STEAM AND GAS POWER ENGINEERING

two ends of the link, then the valve would be affected equally
by both eccentrics. When in this position, very little motion is
given to the valve.

The Walschaeit valve gear, illustrated in Fig. 80, makes use of
a single eccentric placed at an angle of 90° with respect to the
crank. A reversing link pivoted at its center is joined to the
eccentric by means of the eccentric rod and to the lap and lead
lever through the radius rod. The valve is connected directly
to the lap and lead lever, which in turn is connected to the cross-
head by a small link.

Fig. 80. — Walschaert valve gear.

The motion derived from the cross-head moves the valve an
amount equal to the lap plus the lead. The position of the link
block with respect to the link is varied by raising or lowering
the radius rod. By this means, the motion of the engine can
be reversed. When the link block is in the mid-position of the
link, the motion derived from the eccentric is neutralized and the
valve is moved by the cross-head an amount equal to the lap
plus the lead. A and B show two positions of valve gear.

Condensing and Non-condensing Engines. — Non-condensing
engines exhaust directly into the atmosphere, into heating coils,
or into feed water heaters, where the heat contained in the ex-

STEAM ENGINES 107

haust steam is utilized in heating buildings or in raising the tem-
perature of the teed water, as the case may be. Due to the
frictional resistance caused by the steam flowing through the ex-
haust ports, as well as the resistance introduced by the piping and
other equipment, the pressure of the exhaust steam in non-con-
densing engines exceeds atmospheric pressure.

In the operation of a condensing engine, the exhaust steam from
the engine cylinder escapes into a condenser, where it is cooled
and condensed to water, thus producing a vacuum or a reduction
in the back pressure. The reduction in the back pressure increases
the work done in the cylinder, if the cut-off remains constant, by
increasing the mean effective or unbalanced pressure. If the cut-
off is decreased, the same work can be developed by using a
smaller quantity of steam.

Generally a condensing engine will use about 25 per cent, less
steam than a non-condensing engine of the same size on account
of the lower back pressure. Small engines are very seldom oper-
ated condensing, as the gain in economy is usually more than bal-
anced by the increased first cost of the equipment and by the
greater complications of the power plant. A compound engine
when operated condensing will show a greater gain in economy, as
compared with non-condensing operation, than will a simple
engine. The uniflow engine is very economical when operated
condensing. Where the exhaust steam can be used for heat-
ing or for manufacturing purposes, the non-condensing installa-
tion is more practical.

Multiple -expansion Engines. — The use of multiple-expansion
engines is another method for reducing cylinder condensation.
In the simple engine, in which the total expansion of the steam
is accomplished in one cylinder, the cylinder walls are first ex-
posed to the high temperature of the inlet steam and then are
exposed to the low temperature of the exhaust steam. This
causes an excessive loss due to the condensation, which can be
decreased by dividing the expansion into several pressure stages.

As there is a direct relation between the pressure of steam and
its temperature, the decreasing of the pressure range of steam in
a cylinder decreases the temperature range and hence decreases
the condensation losses also. If steam, instead of being expanded
completely in one cylinder, is expanded down to some inter-

108 STEAM AND GAS POWER ENGINEERING

mediate pressure in one cylinder and then is exhausted into a
second cylinder, where its pressure is reduced to that of
the exhaust of a simple engine, the temperature range and
condensation losses within each cylinder are decreased. Such
an arrangement of cylinders forms a multiple expansion engine.
If the pressure range takes place in two stages, the engine is called
a compound; if in three stages, triple expansion; and if in four
stages, quadruple expansion. Obviously the greater the number
of pressure stages, the less will be the temperature range and
hence the better the economy. A triple expansion engine is,
for that reason, more economical than one operating compound,
but the gain in economy when using triple expansion engines is
usually more than offset by the increased cost of the equipment,

Fig. 81. — Tandem compound engine.

the extra floor space required for the additional cylinder, and the
greater complications of the power plant. Triple expansion en-
gines are used in marine practice and in pumping plants, but
are seldom found in steam-electric power plants; ordinarily, the
compound engine is preferable when conditions warrant a multi-
ple expansion engine.

There are two different types of compound engines — the tandem
and the cross compound. This classification depends upon the
arrangement of the cylinders.

In the tandem compound engine, Fig. 81, the axes of the low
and high pressure cylinders are in one straight line. The piston
rod is common to both cylinders and the total force transmitted
to the single crank is the sum of the forces exerted in each
cylinder.

STEAM ENGINES

109

The cross compound engine, Fig. 82, has its cylinders arranged
side by side, and the force exerted in each cylinder is transmitted
to the separate crank pins, usually set at an angle of 90°. By
this arrangement, the turning effort at the crank pin is more
nearly uniform.

Fig. 82, — Cross compound engine.

The Steam Locomobile. — The steam locomobile is a self-con-
tained power plant, which consists of a compound steam engine
mounted upon an internally fired ' boiler. An insulatep! sheet-
metal smoke box incloses both engine cylinders, a superheater,
all steam piping and valves, and a reheater which imparts
heat to the steam as it passes from the high pressure to the low
pressure cylinder. This arrangement utilizes the heat in the
flue gases for superheating the steam before it enters the engine
cylinder, for reheating the steam between the high- and the low-
pressure cylinder, for reducing heat losses within the engine, and
for cutting down the radiation losses of the entire power plant.

The steam from the engine exhausts through a feed-water
heater into a condenser, where it is condensed by direct contact

110 STEAM AND GAS POWER ENGINEERING

with cold water or by contact with tubes through which cole-
water circulates.

Fig. 83 shows a longitudinal section of a steam locomobile with
the various parts named.

Valve Setting. — The object of setting valves on an engine is
to equalize the work done in both ends of the piston. The
method of procedure will vary with the type of valve, but the

STEAM ENGINES

111

general principles will be understood from the following method
used in setting the plain slide valve.

Before a valve can be set, the dead centers for both ends of the
engine must be accurately detei mined.

The method of setting an engine on dead center can best be
understood by referring to Fig. 84. H represents the engine
crosshead which moves between the guides maiked G, N is the
connecting rod, R the crank, F the engine flywheel, and 0 is a
stationary object.

To set the engine on dead center, turn the engine in the direc-
tion in which it is supposed to run, as shown by the arrow, until
the cross-head is near the end of its head end travel, and make

Fig. 84. — Valve setting.

a small scratch mark on the cross-head and guide as at A. At
the same time mark the edge of the flywheel and the stationary
object opposite each other, as at B. Turn the engine past dead
center, in the same direction as shown by the arrow, until the
mark on the cross-head and that on the guide again coincide at
A, and mark the flywheel in line with the same point on the
stationary object, obtaining the mark C. The distance between
the two marks on the flywheel is now bisected at E. If the mark
E on the flywheel is now placed in line with the mark on the
stationary object, the engine will be on the head end dead center.
Similarly, the crank end dead center can be found.

The stationary object may be a wooden board, or a tram
may be used with one end resting on the engine bedplate and

112 STEAM AND GAS POWER ENGINEERING

with the other end used for locating the marks B, C, and E on
the flywheel.

One of two methods may be used in setting the valve. It may
be set so that both ends have the same leads, or so that the point
of cut-off is the same at both ends.

If the valve is to be set for equal lead on both ends, set the
engine on the dead center by the method given above, remove
the steam chest cover, and measure the lead at that end. Move
the engine to the other dead center and measure the lead again.
If the lead on the two ends is not the same, correct the difference,
by moving the valve on the valve stem.

To set the engine for equal cut-off, turn the engine until the
valve cuts-off at one end and mark the position of the cross-head
on the guides. Then turn the engine until the cut-off occurs on
the opposite end and again mark this position of the cross-head
on the guides. If the cut-off occurs earlier at one end than at the
other, change the length of the valve stem until the cut-off is
equalized at both ends.

Setting Corliss Valves. — The setting of Corliss valves is more
complicated than the setting of plain slide valves, but can be
easily accomplished if the customary marks have been placed
upon the various parts by the engine builder. The wrist-plate
support (Fig. 856) is marked by three lines a, c, and b, while the
hub of the wrist-plate itself is provided with one line, d. These
three lines mark the points of the extreme travel as well as the
central position of the wrist-plate when the mark d upon the
wrist-plate hub coincides with its respective mark, a and b, or*
c upon the support. When the back bonnets of the valve
chambers are removed, there will be found marks, i and j
(Fig. 85a), which coincide with the working edges of each of the
steam valves. Similar marks, e and /, on the face of the steam
valve chamber coincides with the working edge of each of the
steam ports. The exhaust valves and their chambers are marked
in a similar manner.

To set the valves, place the wrist-plate in its central position.
This point is found when the mark, d, upon the wrist-plate
hub (Fig. 856) coincides with the central mark, c, upon the wrist-
plate support. Fasten the wrist-plate in this position by placing

STEAM ENGINES

113

a piece of paper between it and the washer which holds the wrist-
plate on the stud. Now with the steam valves hooked up, adjust
the rod M (Fig. 85a) leading from the wrist-plate to the double
arm lever so that each steam valve will have an equal and slight
amount of lap. The amount of this lap varies from 34 6" to
%", increasing with the size of the engine. The exhaust valves
should be similarly adjusted. After the steam and exhaust
valves have been adjusted, the paper between the wrist-plate
and the washer should be removed.

\?-

\ 1
y

Wrist

-Plate

\
\
\

1
1

Engine Cylinder

?*'-..

Wrist- Plate Support^ a f b

Wrist-Plate Hub->
Wrbt Plate*

( b) Method of Marking Wrist-Plate Hub

(a) Rear of Valves with Bonneb Removed

Fig. 85. — Diagram of Corliss valve mechanism.

The rocker arm, with the eccentric rod attached, should now
be placed in a vertical position by means of a plumb line. Loosen
the eccentric on the shaft and adjust the eccentric rod so that the
extreme travel points of the rocker arm are equidistant from the
plumb line. Now connect the hook rod to the wrist-plate and
adjust the length of the hook rod so that when the eccentric is
revolved on the shaft the mark d (Fig. 856) upon the wrist-plate
hub coincides with the extreme travel marks a and b upon the
wrist-plate support.

To adjust the lead, place the engine on one of its dead centers
and turn the eccentric loosely on the shaft in the direction the
engine is to rotate until the steam valve nearest the piston has
the proper lead. Now secure the eccentric to the shaft.

114 STEAM AND GAS POWER ENGINEERING

To adjust the cut-off, secure the governor in its highest posi-
tion and disconnect the wrist-plate from the eccentric. Adjust
the governor cam rods, so that, as the wrist-plate is oscillated,
the releasing of the steam valves in each end of the cylinder occurs
when the port is open about }>i inch. With the governor in its
lowest working position, the releasing gear should not detach
the steam valves.

Replace the valve bonnets and see that all connections have
been properly made. It is always best to oscillate the wrist-
plate a few times to see that the hooks engage properly and that
the dash pot rods are adjusted to a proper length.

Horsepower. — The measurement of the power of an engine is
in terms of horsepower. If work is done at the rate of 33,000
foot-pounds per minute, one horsepower is said to be developed.

Power takes into consideration the time required to do a
certain amount of work and is denned as the rate of doing work.
Work means force times distance through which it acts and is
independent of time. Thus if steam at a pressure of 100 pounds
moves a piston 18 in. in diameter through a distance oi 2 ft., the
work done is 100 times 508.92 (the area of the piston in inches
multiplied by the distance in feet) or 50,892 ft.-lb. The power
of the engine, however, depends on the time that the steam
requires to move the piston through the given distance and, if the
motion is accomplished in 1 second, the power of the engine is
five times greater than if 5 seconds were required.

An engine will have a capacity of 1 hp. if it can do 550 ft.-lb. of
work in a second, 33,000 ft.-lb. of work in a minute, or 1,980,000 ft.-
lb. of work in an hour. To determine the horsepower developed
by any motor or engine, it is necessary to find the foot-pounds
of work which the motor or engine is doing in a minute and divide
this by 33,000. In the example of the previous paragraph, if the
piston passes through the distance of 2 ft. in J£o min., the power
of the engine in horsepower is:

50,8921 = n

33,000 X Ho

Indicated Horsepower. — The term "indicated horsepower'*
(I.hp.) is applied to the rate of doing work by steam or gas in
the cylinder of an engine, and is obtained by means of a special

STEAM ENGINES

115

instrument, called an indicator. The indicator diagrams which
result from the use of such an instrument show graphically the
action of the steam within the engine cylinder, recording the
actual pressure at each interval of the stroke.

One type of indicator is shown in section in Fig. 86. It
consists essentially of a cylinder (4), which is placed in direct
communication with the engine cylinder. Within the cylinder
is the piston (8) to which is attached a spring; as the com-
pression of the spring is proportional to the pressure of the

Fig. 86. — Steam engine indicator.

steam, the movement of the indicator piston is directly propor-
tional to the pressure exerted by the steam. The piston is
attached to the arm ( 16). At the end of the arm is a small pencil
(23) which records the movement of the piston and graphically
indicates the pressure of the steam within the cylinder. At-
tached to the cylinder (4) is an arm which carries the drum (24).
A small paper card to record the motion of the pencil is placed
around this drum. The drum is connected to the cross-head
of the engine, and is provided with a spiral spring, which returns

116 STEAM AND GAS POWER ENGINEERING

it to its original position after being moved outward by the
crosshead.

As the diagram drawn upon the drum of the indicator re-
cords the pressure at every instant of the travel of the piston,
the average unbalanced pressure, called the mean effective
pressure, may be determined and the horsepower calculated.

As an illustration: A steam pump in which a valve without
laps is used has the theoretical indicator card illustrated in Fig.
87. The effective pressure is constant throughout the stroke
and equals 100 lb. per sq. in. This pressure acts upon a 12-in.
(113.1 sq. in. area) piston. Then the total pressure exerted
by the steam is :

<5>

5f-ectm Pressure Line

■Back Pressure Line

<•- Atmospheric Line
Fig. 87. — Theoretical indicator card from direct-acting steam pump.

Total pressure = 100 X 113.1 = 11,310 pounds.
If the stroke of the piston is 12 inches, the work done in
foot-pounds per stroke is:

11,310 X j| •- 11,310.

If this work is exerted upon the piston 50 times per minute, the
work the engine will do per minute, if it is single acting, will be :

11,310 X 50 = 565,500 ft.-lb.
Since 33,000 ft.-lb. per minute is 1 hp., the power of the engine
when single-acting is:

565,500

33,000

= 17.1 1.hp.

As steam engines are usually double-acting, an indicator card
would have to be taken of the crank end, as well as of the head
end, the unbalanced or the mean effective pressure determined
for that end, and the indicated horsepower calculated by the
above method, taking into consideration the size of the piston

STEAM ENGINES

117

rod. The total indicated horsepower of the engine is the sum of
that calculated for the two ends.

Indicator Reducing Motions. — The diameter of the indicator
drum is such that the motion of the drum can only be about
four inches. In driving the drum from a cross-head, whose
motion is in excess of this amount, it is necessary to insert some
form of reducing motion. In other words, some arrangement is
necessary that will reduce the motion of the cross-head so that it
may be reproduced to a smaller scale on the indicator diagram.

♦Cord to Indicator

Fig. 88. — Pendulum reducing motion.

Many indicator reducing motions have been devised, but many of
these do not produce a true reduction. The test of a true reduc-
tion is that, when the cross-head has moved any fraction of its
stroke, the indicator drum has been moved the same fraction of
its total distance, as measured from one of its extreme positions.
One type of reducing motion is illustrated in Fig. 88, and
is often referred to as the pendulum reducing motion. The
pendulum arm A B is attached to the frame of the engine at A.
Its lower end is attached to the cross-head at H, through the
short link. The string to the indicator drum is attached to the
arm A B at such a point that the proper reduction in the motion of
the cross-head is produced. This form of motion is slightly in
error, due to the vertical movement of the point to which the
string is attached.

118 STEAM AND GAS POWER ENGINEERING

A type of reducing motion, called a reducing wheel, is illustrated
in Fig. 89. This type of reducing motion is attached directly to
the base of the indicator and thus eliminates any complicated
connections to the cross-head that are necessary with other types.
The reducing motion consists of two wheels whose diameters may
be proportioned to the stroke of the engine and are connected
to each other through gears. The cord from the indicator drum

Fig

Reducing wheel attached to indicator.

is attached to the smaller wheel, while the larger wheel is con-
nected to the cross-head. Changing the diameters of the two
wheels permits of indicating engines having strokes between
wide limits.

The Indicator Card. — A card taken from a steam engine by
means ot an indicator is shown in Fig. 90. The total length of
the card is proportional to the stroke of the engine, and the
height at any point is proportional to the pressure of the steam

STEAM ENGINES 119

in the cylinder. The events of the stroke in the card are marked :
admission A, cut-off C, release R, compression K. The pressure
may be measured at any point on this card if the scale of the
spring is known. Springs are provided so that various pres-
sures are required to compress the spring sufficiently to cause
the pencil to be moved 1 inch. A 60-pound spring, for in-
stance, will require a pressure of 60 pounds per sq. in. to cause
the pencil point to move 1 inch. Or conversely, if the height
of an indicator card is 1J^ inches at some point in the diagram
and a 60-pound spring is used in making the card, the pressure
exerted by the steam in the cylinder is:

60 X 1M = 90 pounds per sq. in.

Fig. 90. — Steam engine indicator card.

The Measurement of Power from Indicator Cards. — A close
analysis of an indicator card will show that certain pressures
are exerted in the cylinder during the forward stroke and that
lesser pressures exist in the cylinder during the return stroke.
The two series of pressures differ in that those exerted during
the forward stroke act upon the piston of the engine and are
transmitted to the main shaft or flywheel, while on the return
stroke the engine itself, due to the momentum which has been
stored in the various parts during the forward stroke, must force
the steam out of the cylinder and compress it. Thus the total
forward pressure exerted in the cylinder is not effective in
producing power, but some must be utilized to exhaust the steam
and to produce the compression. The effective pressure is the
difference between the total pressure and the back pressure. This
difference is graphically represented by the pressure within
the indicator diagram. To use this value in determining the

120 STEAM AND GAS POWER ENGINEERING

foot-pounds of work, it must be reduced to the mean effective
pressure exerted throughout the stroke. The mean effective pres-
sure (M.E.P.) can best be found by the use of a planimeter, Fig.
91, which is an instrument for measuring areas. Thus

M.E.P. = i rr f -j X scale of spring.

length of card

Fig. 91. — Polar planimeter.

Another means often employed in the absence of a planimeter is
to divide the length of the card into 10 equal parts, as shown in
Fig. 92, and obtain the average of the heights in inches of the 10
trapezoids formed. Thus from Fig. 92

a+b+a+d+e+f+g+h+i+j
10

M.E.P.

X scale of spring.

Fig. 92. — Ordinate method of measuring mean effective pressure.
The indicated horsepower developed by one end of the cylinder

is:

plan
33,000

Where p = mean effective pressure in pounds per sq. in.
I = length of stroke in feet
a = area of piston in square inches
n = number of revolutions per minute

STEAM ENGINES

121

In the crank end of the cylinder this same formula will apply
with the exception that the effective area of the piston is reduced
by the area of the piston rod.

As an illustration, the following data was obtained from the
test of a steam engine:

Diameter of engine cylinder 10 inches (area 78.54 sq. in.).

Diameter of piston rod 1% inches (area 2.405 sq. in.)

Stroke of engine 12 inches

Speed of engine 280 r.p.m.

If the mean effective pressure in the head end side of the cylin-
der is found to be 41.64.

The I.hp. in the head end side is then:

41.64 X ~ X 78.54 X 280

33,000 = 27.73 hp.

The indicated horsepower in the crank end side of the cylinder
is obtained in the same manner, but the effective area in this
side of the cylinder, which is found by deducting the area of the
piston rod, must be used.

If the mean effective pressure in the crank end is 35.76,
the I.hp. in the crank end is then:
12

35.76 X j= X (78.54 - 2.405) X 280

= 23.10 hp.

33,000
The total indicated horsepower developed by the engine is:

27.73 + 23.10 = 50.83 hp.
Valve Setting by Indicator Cards. — In general, one of the best
methods of setting the valve of a steam engine is by means of the

Fig. 93. — Indicator cards,
valves properly set.

Fig. 94. — Indicator cards,
valves improperly set.

steam engine indicator. Any distortion in the events of the
stroke is easily detected, and a little study of such diagrams
suggests the proper steps to correct the difficulty.

122 STEAM AND GAS POWER ENGINEERING

Fig. 93 shows indicator cards taken from the two ends of a
cylinder when the valve is properly set. The four events in

each cylinder occur at very
nearly the same point in each
stroke, and the cards compare
favorably with that of an ideal
diagram.

Fig. 94 shows indicator cards
taken from two ends of a cyl-
inder when the valve is poorly
set. Comparing the cards from
the two ends of the cylinder,
the same events in the two ends
occur at different points in the
stroke; this indicates that an
adjustment of the valve is
necessary.

Fig. 95 shows samples of
good and imperfect indicator
diagrams. The cause of each
defect is explained.

Brake Horsepower. — Brake
horsepower represents the
actual effective power which a
motor or engine can deliver for
the purpose of work at a shaft
or a brake. An instrument for
the measurement of the brake
horsepower of motors, called a
Prony brake, is shown in Fig.
96. This brake consists of two
wooden blocks BB which fit
around the pulley P, and are
tightened by means of the
thumb nuts NN. A projec-
tion of one of the blocks, the
lever L, rests on the platform
scale S. When the brake is balanced, the power absorbed is
measured by the weight, as registered on the scales, multiplied

STEAM ENGINES

123

by the distance through which it would pass in a given time
if free to move. If I is the length of the brake arm in feet,
measured from the center of the shaft to the point of support on
the scales, w the net weight as registered on the scales in pounds,
and n the revolutions per minute of the motor, the horsepower
absorbed can be calculated by the formula:

Brake horsepower =

As an illustration, the net scale reading of an engine running at 250
r.p.m. is 80 lb. If the length of the brake arm is 5J4 feet, cal-
culate the brake horsepower developed.

2 X 3.1416 X 5.25 X 80 X 250

Brake horsepower =

33,000

20.00

Fig. 96. — Prony brake.

Friction Horsepower. — The indicated horsepower of an engine
would be equal to that of the brake horsepower if no losses oc-
curred in the machine. The indicated horsepower is, however,
always in excess of the brake horsepower by an amount equiva-
lent to the power consumed in friction. The difference between
the indicated horsepower and the brake horsepower is conse-
quently the friction horsepower.

F.hp. = I.hp. - B.hp.

Mechanical Efficiency. — The mechanical efficiency of an engine
is the ratio of the brake horsepower (B.hp.) to the indicated
horsepower (I.hp.).

B.hp.

Mech. efficiency =

I.hp.

124 STEAM AND GAS POWER ENGINEERING

The mechanical efficiency is the percentage of the indicated horse-
power that is delivered to the shaft as effective work. One
hundred minus the per cent, mechanical efficiency gives the per-
centage of the indicated horsepower that is lost in friction.

Steam-engine Governors. — The function of a governor is to
control the speed of rotation of a motor irrespective of the power
which it develops. In the steam engine the governor maintains
a uniform speed of rotation either by varying the initial pressure

Fig. 97. — Steam engine governor.

of the steam supplied, or by changing the point of cut-off and
hence the portion of the stroke during which steam is admitted.
Governors which regulate the speed of an engine by varying
the initial pressure of the steam supplied to the engine are called
throttling governors. The throttling governor is the simplest
form of governor, and is used mainly on engines of the plain
slide-valve type. In Fig. 97 is given a section of a throttling
governor, showing details. This form of governor is attached to
the steam pipe at A, and is connected to the engine cylinder at
B, so that the steam must pass the valve V before entering the

STEAM ENGINES

125

engine. The valve V is a balanced valve and is attached to a
valve stem S, at the upper end of which are two balls CC. The
valve stem and balls are driven from the engine shaft by a belt,
which is connected to the pulley P, and which in turn runs the
bevel gears D and E. As the speed of the engine is increased
the centrifugal force makes the balls fly out, and in doing so
they force down the valve stem S, thus reducing the area of the
opening through the valve, and the steam to the engine is
throttled. As soon as the engine begins to slow down, the balls
drop, increasing the steam opening through the valve V. The

**.

y' 1

D ^

spr

-Shaft governor.

speed at which the steam is throttled can be changed within
certain limits by regulating the position of the balls by means
of the nut N.

Most of the better engines are governed by varying the point
of cut-oft and hence the total volume of steam supplied to the
cylinder. In high-speed automatic engines this is accomplished
by some form of flywheel or shaft governor, which controls the
point of cut-off by changing the position of the eccentric.

One form of flywheel governor is shown in Fig. 98. The sheave
of the eccentric is mounted upon an arm which is pivoted to the
flywheel. The eccentric sheave contains a slot which passes
over the shaft, and the outer end of the arm is attached to the
weight as shown. In the operation of the governor, centrifugal

126 STEAM AND GAS POWER ENGINEERING

force causes a movement of the governor weight, and in so doing
the position of the eccentric and hence the cut-off is changed.
As the speed of the engine increases, the cut-off is reduced; and
when the speed slows down the cut-off is increased.

Engine Details. — The general construction of steam-engine
cylinders can be seen from the previous illustrations. Steam-

Fig. 99. — Steam engine piston.

engine cylinders are made of cast iron. As the cylinder wears,
it has to be rebored so as to maintain true inside surfaces. The
thickness of the cylinder walls should be not only sufficient to
withstand safely the maximum steam pressure, but should allow
for reboring. All steam-engine cylinders should be provided with
drip cocks at each end in order to drain the cylinder and steam
chest when starting.

Fig. 100. — Steam engine cross-b

A good piston should be steam tight and at the same time
should not produce too much friction when sliding inside the
engine cylinder. The piston is usually constructed somewhat
smaller than the inside diameter of the engine cylinder, and is
made tight by the use of split cast-iron packing rings. In Fig.
99 is illustrated a piston with its packing rings.

STEAM ENGINES

127

The general construction of steam-engine cross-heads is illus-
trated in Fig. 100. All cross-heads should be provided with
shoes which can be adjusted for wear.

Fig. 101. — Steam engine connecting rod.

Fig. 101 shows a connecting rod. A connecting rod should
be so constructed that the wear on its bearings can be taken
up. This is usually accomplished by wedges and set-screws as
illustrated.

@»

Fig. 102 — Eccentric rod and strap.

Some engines have their cranks located between the two bear-
ings of an engine, and are called center-crank engines. Engines
which have their cranks located at the end of the shaft and on
one side of the two bearings are called side-crank engines.

Fig. 103. — Main bearings.

The eccentric is a special form of crank. It is usually set
somewhat more than 90° ahead of the crank and gives motion to

128 STEAM AND GAS POWER ENGINEERING

the valve or valves in the steam chest of the engine. Fig. 102
shows an eccentric rod and strap.

The main bearings of steam engines are illustrated in Fig. 103.
These bearings are usually made in three or four parts and can
be adjusted for wear by means of wedges and setscrews fastened
with locknuts.

Lubricators. — The function of lubrication is to decrease the
frictional losses which occur in steam engine operation. All
rubbing surfaces at which friction is produced must be lubricated.

Bearings maybe lubricated by
grease cups as illustrated in Figs.
104 and 105. The first type is
used on stationary bearings, the
grease being forced out by screw-

Fig. 104.— Grease cups.

Fig. 105. — Automatic grease cup.

ing the cap down by hand. The type illustrated in Fig. 105 is
automatically operated, and is used for the lubrication of
crankpins.

If oil is used, a sight-feed lubricator is employed, as shown in
Fig. 106. By means of the sight-feed types the flow of oil can
be regulated and the drops of oil issuing from the lubricator can
be seen.

For the lubrication of steam-engine cylinders some form of
sight-feed automatic steam lubricator, as illustrated in Fig. 107,
should be employed. This form of lubricator is used to introduce
a heavy oil into the steam entering the cylinder. This oil is a
specially refined heavy petroleum oil which will neither decom-
pose, vaporize, nor burn when exposed to the high temperature of
steam. Steam from the pipe B leading to the engine cylinder
is admitted through the pipe F to the condensing chamber L,

STEAM ENGINES

129

where it is condensed and flows through the pipe P to the bottom
of the chamber A. The oil which is contained in chamber A rises
to the top, is forced through the tube S, ascends in drops through
the water in the gage glass H, and into the steam pipe K leading
to the steam chest. The amount of oil fed is regulated by the
needle valve E. The gage glass J shows the amount of oil in
the chamber A. In order to fill the chamber A, the valves on
the pipes F and II are closed, the water is drained out through
G, and the cap D is removed for receiving the oil.

Fig. 106. — Sight-feed lubricator. Fig. 107. — Sight-feed automatic lubricator.

Steam Engine Economy. — The economy of steam engines is
usually expressed in pounds of steam consumed per horsepower
per hour. In the case of steam-electric power plants the economy
is expressed in pounds of steam consumed per kilowatt-hour.
The steam consumption of simple, non-condensing engines will
vary, under good operating conditions and at full load, from 20
to 35 pounds per horsepower per hour, depending upon the type
of valve gear used. Compound condensing engines consume
12 to 20 pounds of steam per horsepower per hour.

Reciprocating steam engines are usually operated at steam
pressures varying from 75 to 200 pounds per square inch. The
gain produced in economy by increasing the steam pressure from
80 to 100 pounds per square inch is about twice as great as that
resulting from increasing the steam pressure from 180 to 200
pounds per square inch. In general, the practical limit for steam
9

130 STEAM AND GAS POWER ENGINEERING

pressure is mainly one of expense. The first cost and the cost
of upkeep of steam power plant equipment increases with the
steam pressure.

The exhaust pressure at which an engine is operated depends
upon the use to which the exhaust steam can be put. If the
exhaust steam can be used for heating or for manufacturing
purposes engines are operated non-condensing. With large com-
pound engines the gain due to condensing is considerable. Con-
densing reciprocating engines give best economy with back
pressures of about two pounds absolute (26 inches vacuum).

The quality of the steam influences the losses due to conden-
sation and re-evaporation. The use of superheated steam, con-
sidering the cost of producing the superheat, will increase the net
economy of steam engines by about 5 per cent, for every 100
degrees superheat.

Installation and Care of Steam Engines. — Foundations for
stationary steam engines are usually put in by the purchaser,
the manufacturer furnishing complete drawings for that purpose.
Drawings of a board template are also included. A template
is a wooden frame which is used in locating the foundation bolts
and for holding them in position while building the foundation.

Before starting on the foundation a bed should be prepared for
receiving it. The depth of bed depends on the soil. If the soil
is rocky and firm, the foundation can be built without much diffi-
culty. When the soil is very soft, piles may have to be driven.

The wooden template is then constructed from the drawings,
holes being bored for the insertion of foundation bolts.

Foundations are usually built of concrete. The concrete
mixture should consist of 1 part of cement, 2 parts of sharp
sand, and 4 parts of crushed stone. The stone should
be of a size as will pass through a 2-inch ring. In starting on a
concrete foundation, a wooden frame of the exact shape of the
foundation is built. The template is then placed in position in
the manner shown by Fig. 108, and the bolts are put in, the heads
of the bolts being at the bottom in recesses of cast iron anchor
plates marked P. Often the foundation bolts are threaded at
both ends and the anchor plates are held in place by square nuts.
A piece of pipe should be placed around each bolt, so as to allow
the bolts to be moved slightly to pass through the holes in the

STEAM ENGINES

131

engine bedplate, in case an error should occur in the placing of
the bolts, or in the location of the bolt holes in the engine bed-
plate.

With the frame, template, and foundation bolts in place, the
concrete can now be poured and tamped down. After the con-
crete has set, the template is removed and the loundation is made
perfectly level. It is well to allow a concrete foundation to set
several weeks before placing the full weight of the engine on it.

When the foundation is ready, the engine is placed in position
and leveled by means of wedges The nuts on the bolts are
now screwed down and the engine is grouted in place by means of
neat cement, this serving to fill any crevices and to give the en-
gine a perfect bearing on the foundation.

Fig. 108. — Foundation in the process of construction.

After erecting the engine and all its auxiliaries, including pipes,
valves, cocks, and lubricators, all the parts should be carefully
examined and cleaned, and a coating of oil should be applied
to all rubbing surfaces, cylinder oil being used for the wearing
parts in the valve chest and cylinder.

Before the engine is operated for the first time, it is well to
adjust bearings, and turn the engine over slowly until an oppor-
tunity has been given for any inequalities due to tool and file
marks to be partially eliminated, and also to prevent heating
that might occur if there was an error in adjustment.

When the engine is ready to start, the steam throttle valve should
be slowly opened to allow the piping to warm up, but leaving
the drain cock in the steam pipe, above the steam chest, open to

132 STEAM AND GAS POWER ENGINEERING

permit the escape of condensation. While the piping is being
warmed up all the grease cups and lubricators are filled. Before
opening the throttle valve, all cylinder and steam-chest drain
cocks should be opened to expel water, and the flow of oil started
through the various lubricators. The throttle valve is then
opened gradually, and both ends of the engine warmed up. This
can be accomplished in the case of a single-valve engine by turn-
ing the engine over slowly by hand to admit steam in turn to
each end of the cylinder. In starting a Corliss engine the eccen-
tric is disconnected from the wrist-plate and the wrist-plate is
rocked by hand sufficiently to allow steam to pass through each
set of valves. The drain cocks are closed soon after the throttle
is wide open and the engine is gradually brought up to speed.

When stopping an engine, close the throttle valve. As soon
as the engine stops, close the lubricators, wipe clean the various
parts, examine all bearings, and leave the engine in perfect
condition ready to start.

The above instructions apply to non-condensing engines. If
the engine is to be operated condensing, the circulating and air
pumps should be started while the engine is warming up. The
other directions apply with slight modifications to all types of
steam engines.

In regard to daily operation, cleanliness is of great importance.
No part of the engine should be allowed to become dirty and all
parts must be kept free from rust. It is well to draw off all
the oil from bearings quite frequently and to clean them with
kerosene before refilling with fresh oil. In starting it is well to
give the various parts plenty of oil, but the amount should be
decreased as the engine warms up. An excess of oil should be
avoided.

Competent engine operators usually make a practice of going
over and cleaning every bearing, nut, and bolt, immediately
on shutting down. This practice not only keeps the engine in
first-class condition, as regards cleanliness, but enables the opera-
tor to detect the first indication of any defect that, if overlooked,
might result seriously.

II a knock develops in a steam engine, it should be located and
remedied at once. Knocking is usually due to lost motion in
bearings, worn journals, or cross-head shoes, water in the cylinder,

STEAM ENGINES 133

loose piston, or to poor valve setting. Locating knocks in steam
engines is to a great extent a matter of experience and no definite
rules can be laid down which will meet all cases.

However, one may, by careful attention to the machine, learn
to trace out the location of a knock in a comparatively short
time. He must bear in mind that he cannot rely on his ear for
locating it, as the sound produced by a knock is, in many cases,
transmitted along the moving parts, and apparently comes from
an entirely different point.

A knock, due to water in the cylinder, is usually sharp and
crackling in its nature, while that in the case of a crank or a
cross-head pin is more in the nature of a thud. If the knock
should be due to looseness of the main bearings, the location may
be detected by carefully watching the flywheel. If the cross-
head is loose in the guides the observer may be able to detect
a motion crossways of the cross-head, but it is not likely that he
can do this with accuracy in the case of a high-speed engine; in
such cases the cross-head should be tested when the engine is at
rest. No adjustment should be made in bearings or moving
parts of an engine unless the machine is at a standstill or is being
turned by hand ; never when under its own power.

The heating of a bearing is always due to one of five causes :

1. Insufficient lubrication due to insufficient quantity of oil,
wrong kind of oil, or lack of proper means to distribute the oil
about the bearings.

2. The presence of dirt in the bearings.

3. Bearings out of alignment.

4. Bearings improperly adjusted. (They may be either too
tight or too loose.)

5. Operation in a place where the temperature is excessive.
In case a bearing should run hot and it is very undesirable to

shut down, it is generally possible to keep going by a liberal
application of cold water upon the entire heated surface or sur-
faces. It is sometimes possible to stop heating by changing from
machine oil to cylinder oil which has a higher flash point.

Should a bearing, particularly a large one, be over-heated to
the extent that it is necessary to shut down the engine, do not
shut down suddenly or allow the bearing to stand any length of
time without attention. This is particularly important in the

134 STEAM AND GAS POWER ENGINEERING

case of babbitted bearings, as the softer metal of the bearings
will tend to become brazed to, or fused with, the harder metal of
the shaft, and it may be necessary to put the engine through the
shop before it can be used again.

In case of the necessity of shutting down for a hot bearing,
first remove the load, then permit the engine to revolve slowly
under its own steam until the bearing is sufficiently cool to per-
mit the bare hand to rest upon it.

The presence of water in the cylinder is always a source of
danger, and care should be taken that the water of condensation
is thoroughly drained from the cylinder when the engine is first
started, at shutting down, and at regular intervals throughout the
operation. An accumulation of water may readily cause the
blowing out of a cylinder head with its resultant loss to prop-
erty and possibly to life. There are several appliances now on
the market which automatically safeguard the cylinder head by
providing a weak point in the drain system which will relieve
the excess pressure before the cylinder head gives way.

Problems

1. Examine the power plants in your vicinity and report upon the types
of valve gears used. If the valve mechanisms in any case differ from those
in this text book, hand in clear sketches of such valve gears.

2. Examine the locomotives entering your city and report upon the re-
versing mechanisms used.

3. Check and correct the valve setting of some engine, accessible to you,
and report upon the method used.

4. Explain, using clear sketches, how a Corliss engine is governed.

5. Calculate the indicated horsepower of an 18" X 24" steam engine
operating at a speed of 110 revolutions per minute, if the head-end mean
effective pressure is 30 pounds per square inch, the crank-end mean effective
pressure 30.5 pounds, size of piston rod is 2 inches.

6. An engine operating at a speed of 200 revolutions per minute is tested
by means of a Prony brake. If the length of the brake arm is 42 inches and
the net weight as registered on platform scales 35 pounds, calculate the brake
horsepower of the engine.

7. Prepare a table showing economies which can be expected at full load,
half load, and quarter load, from the following types of engines :

(a) Simple high-speed automatic engines, sizes 50 to 150 horsepower.

(b) Corliss engines, simple and compound non-condensing.

(d) Uniflow engines, condensing and non-condensing.

CHAPTER VIII

STEAM TURBINES

The steam turbine differs from the reciprocating steam engine,
in that it produces rotary motion directly and without any re-
ciprocating parts. The simple steam turbine is a wheel which
is given rotary motion by a steam jet impinging on its blades.
The elastic force of the steam in the turbine does not act upon the
surface of a moving piston, but upon the mass of the steam itself,
converting nearly all of the available energy in the steam between
certain pressure limits, into velocity.

sti>

Fig. 109. — De Laval steam turbine.

In one type of steam turbine, (Fig. 109), the jet of steam from
a fixed expanding nozzle is directed upon moving curved blades.
All the expansion occurs in a nozzle, resulting in a steam jet of
high velocity which does work. This is called the impulse type
of steam turbine. A, B, C, and D are stationary expanding noz-
zles in which the steam is completely expanded and the steam
jet of high velocity strikes the blades V, giving a direct rotary mo-
tion to the wheel W and also to the shaft S.

135

136 STEAM AND GAS POWER ENGINEERING

In another type, called the reaction turbine, (Fig. 129), the
steam is expanded within the stationary and the moving blades
of the machine, and work is partly produced by the reaction of
the expanding steam as it flows from the moving blades to the
stationary or guide blades. No commercial steam turbines
operate upon the pure reaction principle, but work by both the
impulse of the steam against the blades and by the reaction of the
steam as it leaves the blades.

Advantages of the Steam Turbine. — As compared with the
reciprocating engine the steam turbine has the following
advantages:

1. The speed of the steam turbine is practically uniform.
This makes the steam turbine a very desirable motor for electric
central stations.

2. The steam turbine requires no internal lubrication, and the
exhaust steam may be used again without oil filtration.

3. The steam turbine can operate at lower back pressures,
that is at higher vacua, than reciprocating engines. It is not
practical to operate steam engines at vacua greater than 26
inches. Steam turbines are commonly operated at a vacuum
of 28 inches and some turbine installations maintain a vacuum
greater than 29 inches. Increasing the vacuum from 26 to 29
inches increases the energy of the steam very nearly the same
amount as does the increase in steam pressure from 75 to 150
pounds.

4. The steam turbine is better adapted to use highly super-
heated steam than are reciprocating engines equipped with
slide valves or with Corliss valves. With reciprocating steam
engines, other than those equipped with poppet valves, steam
temperature above 450°F., are seldom exceeded. Above such
temperature lubrication is unsatisfactory, and distortion of parts
may take place. Temperatures of 600°F. and higher are common
in steam turbine practice.

5. The steam turbine occupies less space than the reciprocating
engine and weighs less per unit capacity.

6. The steam turbine can be built in very large sizes. Recip-
rocating engines of capacities as great as 10,000 horsepower are
very rare. Steam turbines, each of which has a capacity of 30,000
kilowatt (over 40,000 horsepower) and greater, are found in large

STEAM TURBINES

137

generating stations. In 1918, a 70,000 kilowatt steam turbine
was installed. Other steam turbines varying in capacity from
10,000 to 60,000 kilowatts have been in service in some of the large
central stations from one to five years, operating successfully
from 16 to 20 hours per day.

7. Steam turbines in large sizes are
cheaper than reciprocating engines.

8. Where turbines of large ca-
pacities can be utilized, electric cur-
rent can be generated cheaper than
with reciprocating engines.

History of the Steam Turbine. —
The history of the steam turbine
dates back to the second century
before the birth of Christ, when
Hero of Alexandria contrived a steam motor which is illus-
trated in Fig. 110. The Hero's turbine consisted of a hollow
spherical vessel rotating on two supports. The steam was

Fig. 110. — Hero's Turbine.

Fig. 111. — Branca Turbine.

delivered to the vessel through one of the supports M, and escaped
from it through two bent pipes or nozzles N, N pointed in oppo-
site directions. Rotation of the sphere was produced by the

138 STEAM AND GAS POWER ENGINEERING

reaction due to the steam escaping from the nozzles. The modern
reaction turbine is a modification of the Hero motor.

The Branca Wheel, Fig. Ill, which was designed in 1629,
resembled a water wheel, and was driven by a jet of steam directed
by means of a nozzle upon buckets attached to the wheel.

The steam turbine did not become a commercial success
until near the end of the nineteenth century. The delay in the
practical utilization of the turbine was due to the following
causes :

1. There was very little demand for a high speed motor of
large capacity until the development of the electric central
station.

2. Lack of scientific knowledge concerning the laws governing
the flow of steam has prevented the perfection of a machine
which could operate at practical speeds. All the earlier tur-
bines were single stage machines and operated at very high
speeds. The method of reducing the speed of the turbine shaft,
by passing the steam through a number of wheels in series, was
not discovered until about the middle of the nineteenth century.

3. The simple one wheel turbines, of which the Branca tur-
bine was the prototype, could not be built as commercial motors
until the developments in the science of metallurgy made pos-
sible the manufacture of materials which were capable of bearing
without rupture the high rotative speeds.

The De Laval Simple Impulse Steam Turbine. — The De Laval
steam turbine (Fig. 109) was the first successful simple impulse
turbine. The inventor of this turbine, Dr. Gustaf de Laval,
designed the expanding nozzle in 1889. He also patented the
principle of flexible supports for turbines or other bodies intended
to rotate at high velocities.

Fig. 112 illustrates a sectional plan of a De Laval turbine.
Steam enters the steam chest, where it is distributed to one or more
nozzles, depending on the size, is expanded to the exhaust pres-
sure, and strikes the blades on the turbine wheel C. The nozzles
are generally fitted with stop valves by which one or more nozzles
can be cut out when the turbine is not loaded to its fullest ca-
pacity. The turbine wheel C is mounted on a flexible shaft D
which is supported at the bearings K and 7. After performing
its work, the steam passes into the chamber W, and out through

STEAM TURBINES

139

140 STEAM AND GAS POWER ENGINEERING

the exhaust pipe into the open air or condenser. Since the total
expansion of the steam takes place in one set of nozzles, the
velocity of the wheel in this type of turbine is very high, and this
must be reduced by gearing. The turbine shaft D is connected

Fig. 113. — Nozzles for a De Laval turbine.

to the pinion which engages a gear wheel M, thus reducing the
speed of the shaft Fto that required by the machine to be driven.
A throttling governor T is used for speed regulation.

Fig. 114. — Working parts of a De Laval steam turbine.

Different nozzles are used for condensing and for non-con-
densing operation, as illustrated in Fig. 113. The difference in
the taper of the two nozzles shows graphically the relative ratios
of expansion of steam when expanding against atmospheric

STEAM TURBINES

141

pressure or into a vacuum. A is the steam inlet and B is the
outlet from the nozzle.

The various working parts of a De Laval turbine are illus-
trated in Fig. 114. A is the turbine shaft, B is the turbine wheel,
C is the pinion which meshes with the gear wheel H to reduce the
speed of the shaft L. M is a coupling which connects the shaft
J to the machine to be driven. D, E, F, G, and J are the bearings
for supporting the pinion, the flexible shaft, and the gear wheel
respectively.

Fig. 115. — De Laval governor.

Fig. 115 shows the details of the De Laval governor. It
consists of two weights D which are pivoted on the knife edge
with hardened pins M which bear upon the spring seat J.
When the speed exceeds normal, the weights, affected by centri-
fugal force, spread apart, pressing on the spring seat J, push
the governor pin I to the right, which moves with it the bell
crank lever L. The bell crank lever L operates the main ad-
mission valve, throttling the steam pressure.

When the turbine is operated condensing and overspeeds the
vacuum valve P is operated by the governor allowing air to
enter the turbine exhaust pipe, checking the turbine speed.

142 STEAM AND GAS POWER ENGINEERING

Velocity and Energy of Steam. — The velocity of steam issuing
from a nozzle is theoretically produced by the conversion of
heat energy into kinetic energy. Steam in flowing through a
nozzle is reduced in pressure, and the resulting expansion releases
heat energy which is utilized in accelerating the steam. The
velocit}" resulting when steam is expanded by flowing through a
perfect nozzle may be found from table 6.

Table 6 has been calculated by determining for each of the
various pressures the total available energy (E) which results
when steam at different conditions of quality (X) or of superheats
(S) expands in a perfect nozzle. Each column represents the
change of condition which results when steam at one inlet condi-
tion is expanded through the nozzle. Thus, referring to column
(1), the total available energy at two different pressures repre-
sents the total energy before and after the expansion. The heat
transformed into kinetic energy may then be obtained by the
differences. Knowing the number of heat units available for
transformation, the resulting velocity may be read directly from
the scale.

As an Illustration. — Steam has a pressure of 150 pounds per
square inch absolute, and is superheated 128°F. If the steam
is expanded to a vacuum of 28 inches, or 1.0 pound per square
inch absolute, what will be the velocity of the steam leaving the
nozzle?

Solution. — Steam superheated 128°F. is found opposite the
pressure of 150 pounds per square inch absolute and in column 5,
Table 6.

The total heat energy of the steam (E) is indicated to be
1264 B.t.u. To find the exhaust condition, follow down column 5
until you reach the total energy opposite the 28 inch vacuum
pressure. The total energy (E) for this condition is read, 922
B.t.u.

These values 1264 and 922 represent the total heat energy con-
tained in the steam before and after the expansion. Conse-
quently, the available heat energy utilized in creating velocity
is obtained by subtracting these quantities.

1264 - 922 = 342 B.t.u. per pound.

From the velocity scale, in connection with Table 6, 342 B.t.u.

STEAM TURBINES 143

of heat per pound corresponds to a velocity of 4120 feet per
second.

The energy developed in foot pounds by the steam expanding
in a nozzle can be found by multiplying 778 by the available
energy E, in B.t.u., utilized in creating velocity. In the above
problem, the energy developed by one pound of steam in expand-
ing from 150 pounds absolute to 28 inches vacuum is 778 X
342 = 266,076 foot pounds.

Compound Impulse Turbines. — From the example in the
previous section it is evident that steam attains a very high
velocity, more than three-fourths of a mile per second, when it
expands in a nozzle between a pressure of 150 pounds absolute
and a vacuum of 28 inches. To utilize efficiently the energy of
the steam in a turbine, in which the complete expansion of the
steam occurs in one set of nozzles and the steam at high velocity
is allowed to impinge against a single set of blades, the speed of
the revolving blades should approximately equal one-half the
velocity of the steam. A turbine operating at such a high speed
cannot be utilized for direct connection to machines, but requires
the interposition of a set of reducing gears.

The various compound turbines have been perfected in order
to do away with the reduction gearing of the simple impulse
types. In the simple impulse turbine the complete expansion of
the steam from boiler pressure to exhaust pressure takes place
in one set of nozzles and the velocity acquired in the nozzles is
given up to a single revolving wheel. In one type of compound
impulse turbines the expansion of the steam takes place in a series
of steps or stages, each stage being provided with a set of nozzles
and a single revolving wheel. In another type, the speed is
reduced by giving up the energy of the steam to several revolv-
ing wheels, the direction of the steam between the wheels being
changed by stationary blades.

The Rateau Turbine. — The Rateau turbine, Fig. 116, consists
of a number of stages, each stage including one row of moving
blades and a set of stationary nozzles. The steam enters through
the first set of stationary nozzles, in which it expands to a lower
pressure with a corresponding increase in velocity, and strikes
the first set of revolving blades. The steam next passes through
the second set of stationary nozzles, which are of greater area

144 STEAM AND GAS POWER ENGINEERING

Table 6. — Guide for Determining Velocities Resulting from Expand-
ing Steam in a Perfect Nozzle

Pressure, lb. per sq. in.

Total energy "£,"

and quality

Gage

Absolute

235

250.0

£ = 1135

£ = 1178

£ = 1220

£ = 1266

£ = 1318

X = 0.920

X = 0.971

S = 25°

5 = 107°

S = 206°

185

200.0

£ = 1118

£ = 1160

£ = 1201

£ = 1240

£ = 1294

X = 0.905

X = 0.955

S = 5°

S = 78°

S = 172°

135

150.0

£ = 1096

£ = 1137

£ = 1178

£ = 1219

£ = 1264

X = 0.887

X = 0.935

X =0.982

5 = 42°

S = 128°

110

125.0

£ = 1082

£=1122

£ = 1161

£ = 1203

£=1246

X = 0.877

X = 0.922

X = 0.969

5 = 22°

S=102°

100.0

£ = 1066

£ = 1106

£ = 1145

£ = 1185

£ = 1225

X = 0.865

X = 0.91

X = 0.954

X = 0.998

S = 72°

80.0

£ = 1051

£ = 1090

£ = 1128

£ = 1166

£=1206

X = 0.855

X = 0.898

X = 0.940

X = 0.982

S = 45°

60.0

£=1031

£ = 1069

£ = 1106

£ = 1145

£ = 1182

X =0.842

X = 0.883

X = 0.924

X= 0.965

5=10°

30.0

£ = 987

£ = 1023

£=1058

£ = 1094

£ = 1129

X = 0.814

X = 0.851

X = 0.888

X = 0.926

X = 0.964

atmospheric

15.0

£ = 946

£ = 979

£ = 1013

£ = 1043

£ = 1080

X =0.790

X = 0.823

X = 0.858

X = 0.893

X = 0.928

in. mercury

vacuum

10.0

£ = 923

£ = 955

£ = 988

£ = 1020

£=1053

X = 0.776

X = 0.809

X = 0.842

X = 0.876

X = 0.908

5.0

£ = 886

£ = 916

£ = 948

£ = 979

£ = 1010

X = 0.756

AT = 0.786

X = 0.818

X = 0.849

X = 0.880

3.0

£ = 860

£ = 890

£ = 921

£ = 950

£ = 980

X = 0.742

X =0.772

X = 0.802

X =0.831

X = 0.861

2.0

£ = 840

£ = 870

£ = 899

£ = 928

£ = 958

X=0.731

X =0.760

X = 0.789

X=0.818

X = 0.847

1.0

£ = 810

£ = 837

£ = 865

£ = 894

£ = 922

X = 0.716

X =0.742

X = 0.769

X = 0.797

X =0.823

0.5

£ = 806
X = 0.726

£ = 833
X=0.751

£ = 860
X = 0.777

£ = 888

X = 0 . 802

STEAM TURBINES

145

"A"' or superheat "<S"

>» ,:

«i

•£• M

14.

^£

o —

;^6C0

=-1000

—

=^5-

^^1500

—

50—

# = 1314

ii-2000

■=

5 = 230°

|=§ff"

100-^

#=1294

J-*

5 = 198°

Hf-2500

-E

# = 1270

150 -^

5 = 162°

HJi-

#=1244

# = 1297

=-3000

S = 129°

5 = 228°

JJS.

200-^

# = 1222

# = 1266

H-

—

5 = 68°

5 = 180°

=-3500

250—

# = 1164

# = 1 202

:==

X = 1.00

S = 60°

—

# = 1114

# = 1148

# = 1221

:E=_

X = 0.963

X = 0.997

5 = 100°

^4000

300-5

#=1186

# = 1118

# = 1186

EEL

X = 0.943

X = 0.975

S = 94°

S-

350-^

# = 1041

# = 1172

# = 1134

# = 1168

Z = 0.911

X = 0.942

S = 9°

5 = 82°

#=1010

# = 1040

# = 1100

# = 1130

j=-4500

400-5

Z = 0.890

X = 0.920

X = 0.979

5 = 20°

# = 987

# = 1015

# = 1075

# = 1105

# = 1036

X = 0.875

X = 0.913

X = 0.961

AT = 0.990

S = 45°

450~5

# = 950

# = 978

# = 1034

# = 1062

#=1090

=="

X = 0.851

X = 0.878

X= 0.932

X = 0.959

X = 0.987

EEr-

■Jj

# = 914

#=941

#=995

# = 1022

# = 1049

EEl5000

500^

A* = 0.828

X = 0.854

X = 0.905

Z = 0.931

X = 0.957

Velocity
Scale

146 STEAM AND GAS POWER ENGINEERING

than the first, because the volume of steam was increased by its
expansion in the first set. Here the steam again expands and

enters the second row of moving blades, and the process is repeated
in succeeding stages until the steam reaches the exhaust outlet.

STEAM TURBINES

147

The Kerr Turbine. — The Kerr steam turbine, illustrated in
Fig. 117, is similar to the Rateau in that the expansion of the
steam takes place in a series of stages, each stage being provided

Fig. 117. — Kerr steam turbine.

with a set of nozzles and a single revolving wheel. The expan-
sion in a Kerr turbine is carried out in from six to ten stages.
The steam is partly expanded in the first set of nozzles, and the
energy developed is abstracted by the first revolving wheel.
The steam then expands in a second and subsequent set of nozzles
until the steam from the last revolving wheel enters the exhaust.

A single stage simple impulse
turbine with double cup-shaped
blades is illustrated in Fig. 118.
This type of turbine was formerly
manufactured by the Kerr Com-
pany.

The Kerr steam turbine is gov-
erned by a centrifugal spring-loaded
throttling governor mounted directly
on the turbine shaft, and acting
through suitable connections upon
the steam valve stem. An emergency governor, entirely inde-
pendent of the main governor, shuts down the turbine, when it
overspeeds, by closing a valve in the steam line.

Fig. 118.— Turbine with
double cup-shaped blades.

148 STEAM AND GAS POWER ENGINEERING

De Laval Multiple Impulse Turbine.- — The De Laval multiple
impulse turbine is illustrated in Fig. 119. It consists of a series
of blade wheels which revolve in independent chambers formed
between diaphragms held in the casing of the turbine. Steam
is admitted to the steam chest at the right hand end of the tur-
bine and is directed by means of nozzles upon the blades of
the first revolving wheel. The steam leaving the first revolving
wheel passes through guide blades, which are set around the

Fig. 119. — De Laval multiple-impulse steam turbine.

entire periphery of the diaphragm separating the first and second
stages, and strikes the blades of the second revolving wheel, and
so on through the succeeding stationary and revolving blades.

The governing of the De Laval Multiple impulse turbine is
accomplished by throttling the admission of the steam to the
steam chest. An emergency governor is mounted in the end of
the turbine shaft, entirely independent of the main speed gover-
nor, and can be adjusted to act at any predetermined speed.

De Laval multiple impulse machines are provided with reduc-
tion gears for the driving of machines at slow speeds.

STEAM TURBINES

149

The Terry Turbine. — The principle Gf the Terry turbine is
illustrated in Fig. 120. This turbine consists of one set of nozzles
and one revolving wheeL The steam is expanded in the nozzle

Section Thrud-A '
Fig. 120. — Terry steam turbine.

from approximately boiler pressure to exhaust pressure. The
jet of steam issuing from the nozzle N, at high velocity,
strikes the side of the wheel blades, is reversed in direction

Fig. 121. — Parts of a Sturtevant turbine.

180 degrees, and is guided into one of the stationary reversing
blades R, by means of which the jet is redirected a second time
on the buckets B of the wheel. This process is repeated several

150 STEAM AND GAS POWER ENGINEERING

times until all the available energy of the steam has been ab-
stracted by the revolving element.

The Sturtevant Turbine. — The Sturtevant turbine (Fig. 121)
is similar to the Terry turbine in that the steam from the moving
blades is diverted back into the stationary blades next to the
nozzle. A sectional view through a Sturtevant turbine is shown
in Fig. 122. A throttling governor is used to regulate the speed
of this turbine.

Fig. 122. — Sectional view of a Sturtevant turbine.

The Westinghouse Impulse Turbine. — The Westinghouse
impulse turbine operates on the same principle as the Sturte-
vant and Terry turbines.

The Curtis Steam Turbine. — In the Curtis steam turbine,
the expansion of the steam takes place in several stages and the
velocity acquired in the nozzles of each stage is abstracted by
one or two revolving wheels. The number of stages varies
from four to nine or more, depending upon the size of the machine.
In very small sizes the Curtis turbine is built as a one stage
machine, with two or three revolving wheels.

STEAM TURBINES

151

The action of the Curtis turbine is illustrated by Fig. 123.
Steam at boiler pressure enters through one or more admission
valves B into the steam chest C. The steam from the steam chest

Fig. 123. — Arrangement of nozzles and blades in two-slage Curtis steam turbine.

enters the expanding nozzles D. The number of admission
valves used is controlled by the governor in accordance with the
load. The steam jet at high velocity issuing from the nozzle D

Fig. 124. — First stage nozzle plate for a Curtis turbine.

strikes the moving blades F} giving up a portion of its energy.
The direction of the steam is changed by the stationary or guide
blades G, called intermediates, striking the second set of moving

152 STEAM AND GAS POWER ENGINEERING

blades H. The steam issuing from the second set of moving
blades enters the second stage, where it is further expanded by
means of nozzles K and the energy developed is abstracted by

Fig. 125. — Blading of Curtis turbine.

\_J

avS

JU"3

M i

,,„„. _ : .

r ■ \ x **

! v Y 1

7TT%

**rr

^T =&? '

Fig. 126. — Horizontal Curtis steam turbine.

moving blades M. The same operation is repeated in the third
and in the subsequent stages.

The expanding nozzles of the first stage of a Curtis turbine

STEAM TURBINES

153

are illustrated in Fig. 124. These extend around a relatively
short arc of the periphery in the first stage, while in the low
pressure end they extend around the entire wheel.

Fig. 127. — Vertical Curtis steam turbine.

The method used in fastening blades of a Curtis turbine is
illustrated in Fig. 125.

The Curtis turbine is constructed as a horizontal machine

154 STEAM AND GAS POWER ENGINEERING

(Fig. 126). The vertical arrangement (Fig. 127), used in some
of the earlier designs, is now obsolete, but units of this type
can still be found in operation in many of the large power
plants. In the vertical turbines the shaft is supported by a
step-bearing at the lower end. Oil is pumped under this bear-
ing at considerable pressure, thus floating the entire revolving
element on an oil film.

Small Curtis turbines are controlled by means of a throttling
governor. Large turbines are controlled by an indirect type
of governor, which mechanically or through a pilot valve and

Fig. 128. — Hydraulic governor for Curtis turbine.

a hydraulic cylinder opens or closes the admission valves, thus
regulating, in accordance with the load, the number of nozzles
which are open for the discharge of steam. The hydraulic type
of governor for Curtis turbines is illustrated in Fig. 128.

Curtis turbines are equipped with an automatic emergency
governor, independent of the main governor, which through a
trip operates the main throttle valve when the turbine speed
exceeds a predetermined limit.

The Reaction Turbine. — The reaction steam turbine differs
from the impulse turbines in that stationary blades are substi-
tuted for nozzles. The blades are shaped so that they can per-

STEAM TURBINES

155

form the functions of the nozzles and of the blades of impulse
turbines. The reaction turbine has many stages, each stage
consisting of a set of stationary and of rotating blades. Part
of the expansion of the steam takes place in the stationary blades
and part in the moving blades. In the impulse turbine the pressure
on both sides of the moving wheel is very nearly the same; in the
reaction turbine the pressure at the inlet to the wheel blade is
greater than the pressure at the outlet.

The Parsons Turbine. — The principle of the single flow
Parsons reaction turbine is illustrated in Fig. 129.

Fig. 129. — Sectional view of a Parsons turbine.

The steam enters a governor valve, reaches the chamber I
and passes out to the right through the turbine blades, eventually
arriving at the exhaust chamber E. The areas of the passages
increase progressively in volume, corresponding with the expan-
sion of the steam.

The rotating part of the turbine consists of a long drum upon
which are mounted the moving blades. The stationary or guide
blades are fitted in rings fastened to the turbine casing.

On the left of the steam inlet are shown the revolving balancing
pistons, one corresponding to each cylinder or section of the
turbine. The steam at / presses against the turbine and goes

156 STEAM AND GAS POWER ENGINEERING

through doing work. It also presses in the reverse direction,
but cannot pass the piston, thus equalizing the pressure and
reducing end thrust on the shaft. In most designs of Parsons
turbines all the balancing pistons are at the pressure end of
the turbine. In the Allis-Chalmers Parsons turbine the largest
balancing piston is placed at the low pressure end of the rotating
element behind the last row of blades.

At T is shown a thrust bearing which serves to maintain the
correct adjustment of the balancing pistons. Q is a pipe con-
necting the back of the balancing piston at S with the exhaust
chamber E', to insure that the pressure at this point should be the
same as that of the exhaust. The governor gear and oil pumps
generally receive their motion by means of a worm wheel, gearing
into a worm cut on the outside of the coupling. An oil reservoir
is provided into which drains all the oil from the bearings. From
there it flows to a pump to be pumped to a chamber, where
it forms a static head which gives a continuous pressure of oil to
the bearings. A by-pass valve is provided, this valve admit-
ting high-pressure steam to the lower stages. By opening this

valve the turbine can carry
considerable overload or to
operate non-condensing at
nearly full load.

Reaction turbines are
controlled by an indirect
type of governor, which
causes the main steam ad-
mission valve to remain
open for longer or shorter
periods of time, depending
upon the load carried by the machine. The governor is of the
fly ball type and is illustrated diagrammatically in Fig. 130.

The governor levers (Fig. 130) are attached to the small relay
valve which operates the main admission valve. The levers receive
reciprocating motion at C from an eccentric and use the governor
clutch as a fulcrum, points D and E being fixed. Continuous
reciprocating motion is thus given to the relay valve. This is in
turn transmitted to the admission valve. The function of the
governor is to vary the plane of oscillation of the relay valve,

Fig. 130. — Governor for Parsons turbine.

STEAM TURBINES

157

which causes the admission valve to remain open for a longer
or shorter period, according to the position of the governor.

*mH

""'^^^SfiNfcv ^" '~* H '/

■P^a ' ' [

Fig. 131. — Westinghouse-Parsons turbine with the upper casing removed.

Fia. 132. — Blading of Westinghouse-Parsons turbines.

Thus the steam is admitted in puffs, which occur at constant
intervals of time. The puffs are either of long or short duration

158 STEAM AND GAS POWER ENGINEERING

according to the load. At heavy loads the puffs merge in a con-
tinuous blast. With this type of governor high-pressure steam
is used at all loads.

A Westinghouse-Parsons turbine with its upper casing re-
moved is illustrated in Fig. 131. The method used in fastening
the blades of a Westinghouse-Parsons steam turbine is illus-
trated in Fig. 132.

The Impulse-reaction Turbine. — A section through a com-
bined impulse and reaction turbine is shown in Fig. 133. The

WW t**^

Fig. 133. — Double-flow Westinghouse turbine.

impulse element is similar to the first stage of a Curtis turbine,
and consists of one set of nozzles, an impulse wheel with two
rows of revolving blades, and a set of stationary blades. Steam
first enters the turbine nozzles, is partly expanded, and impinges
upon the impulse blades. The remaining energy of the steam
after leaving the impulse blades is utilized in the reaction element
of the turbine.

The impulse-reaction turbine occupies less space than the
pure reaction machine. It is constructed either as a single flow or
as a double flow machine. In the single flow the reaction elements

STEAM TURBINES

159

are on one side of the impulse stage, while in the double flow
(Fig. 133) the reaction elements are on both sides of the impulse
wheel.

The Spiro Steam Turbine. — The Spiro steam turbine, which

Fig. 134. — Rotors of the Spiro turbine.

is illustrated in Figs. 134 and 135, consists of two herringbone
gears in mesh which revolve in a close-fitting casing. Steam is
admitted at mid-length into the tooth pockets at the point A of
each rotor. As the rotor turns, the tooth space occupied by the

Fig. 135. — Casing or cylinder of the Spiro turbine.

steam increases in length and the steam expands. The steam
escapes when the outer ends of the teeth pass the line of contact
between the two rotors. The inlet port openings are situated
one on each side of the central rib, as illustrated in Fig. 135.
This turbine is governed by throttling the steam.

160 STEAM AND GAS POWER ENGINEERING

The Spiro steam turbine is not suitable for condensing opera-
tion, but is compact and is used for the driving of pumps, fans,
and other auxiliaries in connection with power plants, office
buildings, and factories.

Exhaust Steam Turbines. — A steam turbine installed between
the exhaust of a reciprocating engine and a condenser is called
an exhaust steam turbine. The reciprocating steam engine does
not show as high an economy at high vacuum as does the steam
turbine. The capacity and economy of reciprocating engine
steam power plants have been increased by the addition of a low
pressure turbine.

Exhaust steam turbines may be operated as straight low pres-
sure turbines using only exhaust steam from engines, or as
mixed pressure turbines which operate on high and low pressure
steam at the same time.

Ordinarily, combined reciprocating engines and low pressure
steam turbines would not be selected for a new installation, as
the cost of the combined units is much greater than that of the
high pressure steam turbine. The field of the low pressure steam
turbine is in connection with the large non-condensing reciprocat-
ing engine power plant.

Applications of the Steam Turbine. — The steam turbine is
applicable to work which requires a high and constant rotative
speed, where a high starting effort is not required, and where
there is no need of reversing the direction of motion. These
conditions exist in electric generating stations. For service in
which the speed is low and variable, where a reversal of direction
is necessary, or where the starting torque is high, the turbine is
unsuited and the reciprocating engine is better adapted. Speed-
reduction and reversing gears have been employed in connection
with turbines, but these have only a limited application.

The steam turbine is very seldom operated non-condensing;
in power plants where the exhaust steam is used for heating or
for manufacturing purposes the reciprocating engine will
usually be found more satisfactory.

Steam turbines are used to some extent for the driving of power
plant auxiliaries, such as boiler feed pumps, hot well pumps and
circulating pumps; also high pressure fans and blowers.

Steam turbines are also employed for the propulsion of ships.

STEAM TURBINES 161

The steam turbine has less weight and requires less space than
the reciprocating engine of the same size. Vessels propelled
by steam turbines are more stable on account of the lower center
of gravity of the machinery. The steam turbines are usually
connected to the propellers by means of gears. In some cases the
steam turbine drives an electric generator and the propellers are
driven by electric motors, which receive their current from the
generator of the turbine.

Steam Turbine Economy. — The economy of steam turbines
is usually expressed in pounds of steam per kilowatt hour,
as the greatest field of the turbine is for the driving of electric
generators. Steam turbines in sizes of 1,000 to 10,000 kilowatt,
when operated at 150 to 200 pounds gage pressure, with super-
heats of 100° to 200°F. and with a vacuum of 28 to 29 inches,
will develop a kilowatt on 12 to 15 pounds of steam per hour.
Better economies are secured as the size of the unit increases.
The smaller condensing steam turbines, when operated with
saturated steam, will consume 18 to 30 pounds of steam per kilo-
watt per hour. Steam turbines when operated non-condensing
will consume 50 to 75 pounds of steam per kilowatt per hour.

Steam turbines under ordinary operating conditions will show
a gain of about 8 per cent, for each 100 degrees superheat. The
presence of moisture will decrease the economy or increase the
steam consumption by about 2 per cent, for 1 per cent, of mois-
ture in the steam. Increasing the vacuum from 27 to 28 inches
will increase the turbine economy from 3.0 to 5 per cent. In-
creasing the steam pressure from 150 to 200 pounds will increase
the economy about 3 per cent.

Installation and Care of Steam Turbines. — The general rules
given in Chapter Vll concerning the installation and care of
reciprocating steam engines apply also to steam turbines.

The steam turbine should be located so that it will be acces-
sible from all sides for inspection and repair. Proper crane and
hoist facilities should be available for all parts which are too
heavy to be handled by hand.

The foundation should be sufficiently heavy to afford a per-
manent support and rigid enough to prevent springing or
warping any part of the turbine. To prevent vibrations from
being conducted to the building, a space should always be left
li

162 STEAM AND GAS POWER ENGINEERING

between the turbine foundation and the walls or floors; this
space should be filled with some soft material. After the founda-
tion is properly set, care must be taken to obtain proper adjust-
ment of the turbine. Small steam turbines are usually placed on
concrete floors without foundations.

The piping must be so designed and installed that no strain
will be thrown on the turbine due to expansion and contraction,
or on account of the piping being improperly supported. Water
pockets in the piping should be avoided.

Before starting a steam turbine for the first time, care must be
taken to blow out the steam and oil from the piping in order to
remove scale and dirt. The oiling system should then be put
in operation and the turbine should be warmed up and started
slowly, listening for any clicking or rubbing sounds, which may
require investigation. While the turbine is turning over slowly
the oiling system and the auxiliaries should be examined.
Heating of the bearings may be due to grit or to poor alignment.
After ascertaining that everything is in good working order, the
turbine should gradually be brought up to speed. As the tur-
bine approaches full speed, the action of the governor should be
observed. If the governor is working properly, the turbine is
ready for the load.

In starting a condensing turbine, the condenser auxiliaries
are started first, and after the vacuum has been obtained, the
turbine is started.

Problems

1. To gain a conception as to the enormous amount of power a 70,000
kilowatt turbine develops, calculate the following:

(a) If all the energy of a 70,000 kilowatt turbine is used to supply light,
calculate the number of candle power it will supply by means of Tungsten
lamps.

(b) If a 70,000 kilowatt turbine develops a kilowatt on 2}4 pounds of
coal per hour, calculate the amount of fuel required to keep such a turbine
in operation at full load for ten hours.

2. Calculate, using Table 6, the energy in foot pounds which will be
developed when steam, initially 2 per cent, wet, expands in a perfect nozzle:

(a) From 150 pounds absolute to atmospheric,

(6) From 150 pounds absolute to 28 inches vacuum.

3. Calculate and compare the velocities developed by:
(a) Water falling through a head of 200 feet.

STEAM TURBINES 163

(b) Steam, initially dry, expanding in a perfect nozzle from a steam
pressure of 200 pounds absolute to a vacuum of 29 inches.

4. Show by means of clear sketches the details of governors used in
connection with:

(a) Simple impulse turbines,
(6) Curtis turbines,

6. Explain how vessels propelled by steam turbines are reversed.

CHAPTER IX

ENGINE AND TURBINE AUXILIARIES

Many of the auxiliaries which properly belong to the engine
and turbine have been described in Chapters IV, V, VI, VII,
and VIII. This chapter will deal mainly with condensers and
condenser auxiliaries, but will include other apparatus which
can be called auxiliaries or accessories to an engine or turbine.

Condensers

The Principle of the Condenser. — The advantage gained by
operating a steam engine condensing is due to the reduction in
the back pressure against which the engine exhausts. In the
case of the steam turbine, the available energy in the steam can
be more than doubled by carrying high vacua, as compared
with non-condensing operation.

The gain in economy which can be expected by increasing the
vacuum depends to some extent upon the size of engine or turbine,
and also upon the type of machine. The theoretical gain for a
perfect steam motor per inch of vacuum will vary from about
3.0 per cent, at 25 inches vacuum to about 5.0 per cent, at 28
inches vacuum. A well designed steam turbine will very nearly
realize the theoretical gains for any given vacuum. A high
vacuum means low temperature condensed steam, and this may
necessitate the heating of condensed steam before it is used as
boiler feed water.

If an engine or turbine is provided with some vessel into which
the steam is exhausted, vacuum could be maintained by simply
removing the uncondensed exhaust steam as fast as it enters.
Such a method, however, would not be economical, as the equip-
ment utilized in maintaining the vacuum would have to handle
practically the entire volume of exhaust steam leaving the engine.
If this were the case, very little gain would result, for as much
work would have to be done by the condenser pump in main-
taining the lower back pressure as would be gained by the engine.

164

ENGINE AND TURBINE AUXILIARIES 165

Steam, however, may easily be condensed, and in the form of
water occupies a very much smaller volume. Advantage of this
fact is taken in the operation of condensers. Thus, if the exhaust
steam from the engine is admitted into a vessel and condensed
before being discharged, the work required to maintain the vacuum
is greatly reduced, because the work of the condenser pump is
only that due to the removal of a comparatively small volume
of water.

In a system composed entirely of steam, or one in which the
exhaust steam was not mixed with air or with other gases which
have entered the system, the vacuum to be maintained is depend-
ent upon the temperature of the condensed steam. By refer-
ence to the steam tables (Table 5), it will be found that water at
a temperature of 126.1 degrees Fahrenheit boils at a pressure of
2 pounds absolute. A condenser in which the condensed steam
is at that temperature would be limited to that pressure. Any
attempt to lower the vacuum would cause an evaporation of the
condensed steam.

In the actual operation of condensers the temperature of the
condensed steam must be below that corresponding to the
vacuum to be carried. The condenser is never free from air and
the temperature of the condensed steam is several degrees below
that corresponding to the vacuum carried. Air enters with the
boiler feed water and also leaks in the condenser through piping
and valves. The air mixed with the steam not only tends to
destroy the vacuum and raise the pressure in the condenser above
that theoretically required, but must also be continuously
removed, if the vacuum is to be maintained.

The Measurement of Vacuum. — The pressure maintained in
a condensing system may be measured by a mercury manometer
or by a special gage. The pressure is below that of the atmos-
phere, hence the term vacuum is- applied.

The measurement of pressures above that of the atmosphere is
expressed in pounds gage. In the measurement of pressures
below atmosphere, the unit of pressure is usually stated in inches
of mercury and expresses the amount of pressure below that of
the atmosphere. To convert pressure above atmospheric to
absolute pressure, the gage pressure is added to the atmospheric
pressure, corresponding to the barometric reading. When

166 STEAM AND GAS POWER ENGINEERING

vacuum readings have to be converted into absolute pressures,
the pressure corresponding to the vacuum must be deducted
from the atmospheric pressure.

As an illustration, a condensing engine receives steam at
100 pounds per square inch gage and exhausts into a condenser
whose gage reads 26 inches of mercury. The barometric pres-
sure is 29 inches of mercury.

A column of mercury 1 inch high is equivalent to a pressure
of 0.491 (roughly %) pounds per square inch, or the equivalent
pressure of the atmosphere is then :

29 X 0.491 = 14.24 pounds per square inch.
The absolute pressure of the entering steam is:

100 + 14.24 = 114.24 pounds per square inch.

Since the vacuum in the condenser is measured in units below
atmospheric pressure the absolute pressure within the condenser
is:

29 — 26 = 3 inches of mercury
which is equivalent to ■

3 X 0.491 = 1.47 pounds per square inch absolute.

Types of Condensers. — Condensers are either of the jet or of
the surface type. The jet condensers produce condensation
by the direct mingling of the exhaust steam and circulating water,
and the resulting mixture of condensed steam and water leaves
the condenser at the same temperature. In the surface con-
denser, the exhaust steam and the circulating water are separated
by tubes, the heat transfer between the steam and circulating
water taking place by conduction through the tubes.

The jet condenser is much simpler than the surface condenser
and its first cost is lower, but in most cases it is restricted in its
application to plants where the injection water is good. The
surface condenser has the advantage in that its cooling water
does not come in direct contact with the steam to be condensed.
For this reason surface condensers are used where the condensed
steam is returned to the boiler, and where the cooling water is
salty, muddy, or otherwise unfit for steam making. While the
surface condenser is particularly well suited for plants where the
circulating water is poor, it must not be inferred that it would be
practical to use water so filthy that it would foul the tubes.

ENGINE AND TURBINE AUXILIARIES

167

Jet Condensers. — Fig. 136 illustrates the construction of one
of the simpler types of jet condensers. Exhaust steam enters
at A. Injection water enters at B, and is divided into a fine
spray by the adjustable valve D. The steam is condensed by
contact with the finely sprayed water, and
the mixture accumulates in chamber F,
from which it passes to the pump G and
is discharged at J. The pump G in this
type of condenser must remove both the
air and the condensed steam. It is called a
wet air pump. The pump cylinder in order
to handle the air and the condensed steam
must be designed larger than would be
required for the removal of the water
alone.

Injection water under pressure is not
necessary with this type of condenser, as
the water will be drawn into the con-
densing chamber by the vacuum produced,
although the pumping head in such cases
is limited to about 15 feet. With such an

Fig. 136. — Jet condenser.

arrangement, means must be provided for creating a vacuum when
starting the condenser. This is usually accomplished by start-
ing the pump or by providing the condenser with an auxiliary
supply of injection water under pressure, which will produce
sufficient vacuum by condensing the first steam admitted.

168 STEAM AND GAS POWER ENGINEERING

Condensers are usually provided with some means for auto-
matically breaking the vacuum. The atmospheric relief valve,
illustrated in Fig. 137, is placed in a branch taken from the main
exhaust line between the condenser and the engine, and leading
to the atmosphere. The atmospheric exhaust valve is held
closed by the atmospheric pressure when the vacuum is main-
tained, but should the vacuum be lost the pressure of the exhaust
steam operates the valve, permitting a free outlet of the steam to
the atmosphere. When the vacuum is restored, the valve will
automatically close.

Fig. 137. — Atmospheric relief valve.

Barometric Condensers. — Fig. 138 illustrates the barometric
type of jet condenser. The condensing chamber is supported
upon a water -sealed tail pipe, 34 feet above the surface of the
water in the hot well. Atmospheric pressure at sea level will
support a column of water 34 feet high, consequently the accu-
mulation of condensed steam in the tail pipe which would tend to
rise above this height, will displace an equal quantity of water
from the bottom of the tail pipe. No pump is required for the
removal of the condensed steam from the barometric condenser,
but in most cases the use of a pump for the injection water is

ENGINE AND TURBINE AUXILIARIES

169

necessary. If the cold water supply is within a vertical distance
of 20 feet from the injection opening to the condenser, the use of

water distributing

TRAY

AlR PUMP SUCTION

Fig. 138. — Sectional views of a barometric condenser.

a pump for the injection water may be dispensed with, as the
vacuum will lift the water to that extent.

170 STEAM AND GAS POWER ENGINEERING

Ejector Condensers. — The ejector, eductor, and siphon
types of jet condensers depend upon the high momentum of the
condensed steam and cooling water to discharge the condensate

Fig. 139. — Ejector condensers.

against atmospheric pressure. No circulating or air pump, or
barometric tube is needed. Fig. 139 illustrates two different
types of such condensers. Exhaust steam enters the eductor

ENGINE AND TURBINE AUXILIARIES 171

condenser at E, completely fills the annular chamber A, and
passes through the small nozzles. The cooling water is con-
tinuously drawn in through the nozzle C and meets the condensed
steam in the tube T. Condensation takes place and sufficient
velocity is developed to remove the condensed steam, the cooling
water, and the air.

Surface Condensers. — A sectional elevation through a surface
condenser is shown in Fig. 140. It consists of a cylindrical or
rectangular cast iron shell closed at the two ends by suitable
heads. Attached to the inner surface of the condenser shell
are two tube plates, which are joined by numerous seamless drawn-
brass tubes.

Exhaust steam enters the top of the condenser and strikes
a baffle plate which protects the upper rows of tubes and dis-
tributes the steam to all parts of the condenser. Circulating
water enters at the end of the condenser, and passes through the
various banks of tubes as shown by the arrows. The steam flows
around the tubes and is condensed by coming in contact with
the cool surfaces.

In the condenser illustrated, the circulating and wet air pump
form the base upon which the condenser rests, although this
arrangement is not always adhered to. The pumps (Fig. 140)
are connected by a common piston rod which is operated by the
central steam cylinder.

Vacuum Pumps

In connection with a condenser installation, a wet-air pump
and a circulating pump are required. To maintain a high vacuum,
a dry-air pump is used in addition to a hot-well pump and a water
circulating pump. The power consumed by the condenser aux-
iliaries is about 2 per cent, of the total output of the unit the
condenser serves. Wet-air pumps are used to remove the con-
densed steam, the non-condensible vapors, and the cooling water.
Dry-air pumps remove only the non-condensible vapors, and
are used in steam turbine installations where a high vacuum must
be maintained. Hot-well or condensate pumps are those that
remove the condensate from surface condensers; circulating
pumps force the cooling water through the condenser.

172 STEAM AND GAS POWER ENGINEERING

ENGINE AND TURBINE AUXILIARIES

173

Wet-air Pumps. — A type of wet-air pump commonly used in

connection with jet condensers is illustrated in Fig. 141. These

pumps are of the reciprocating type. On the upward stroke of

the piston, a lower pressure

than that maintained in the

condenser is created below

the piston, causing the cool-
ing water and condensate,

together with the air, to be

drawn into the cylinder. The

downward stroke of the piston

causes the foot val ves to close

and the entrapped water and

air to pass through valves in

the piston. When the piston

next moves upward the mix-
ture is compressed by the

closure of the valves in the

piston and is discharged

through the valves at the top

of the cylinder.

Edwards Air Pump. — Fig. 142 illustrates a type of wet-air

pump designed for use with surface condensers. Pumps that

depend upon foot valves for the entrapping of the air and water in

the pump cylinder require an appre-
ciable difference in pressure to insure
the opening of the val ves. The Edwards
air pump, by the elimination of these
valves, is capable of maintaining a vac-
uum from Y^ to 1 inch lower than would
be possible with pumps of the valve
operated type.

The condensed steam flows by grav-
ity from the condenser to the pump,
where it collects in the base. Upon

Fig. 142.-Edwards air pump. the degcent Qf the CQnical shaped pistons

or bucket, the water is projected at high velocity through the
ports into the working barrel of the pump, drawing with it con-
siderable air and other non-condensible vapors. On the upward

Fig. 141. — Wet-air pump.

174 STEAM AND GAS POWER ENGINEERING

stroke, the ports are closed by the piston, and the water and
entrapped air is discharged through the valve at the top of the
cylinder.

Dry-air Pumps. — For high vacua, it is more desirable to dis-
charge the air and condensate from the condenser separately.
This arrangement necessitates the use of two pumps, a dry-air
pump and a wet-air pump.

Fig. 143 illustrates a sectional view of an Alberger dry-air
pump. The suction valve is positively actuated by an eccentric

Fig. 143. — Dry-air pump.

on the crank shaft. This valve is provided with an equalizing
port, which eliminates the detrimental influence of the air in the
clearance space.

When the piston reaches the end of the stroke, the space be-
tween it and the cylinder head is filled with air at atmospheric
pressure that has not been discharged through the outlet valve.
If the piston were to make the return stroke while this air was
under pressure, a considerable part of the stroke would be tra-
versed by the piston before this air had expanded to the suction
pressure. As a result the drawing in of a fresh charge of air

ENGINE AND TURBINE AUXILIARIES

175

from the condenser would be confined to a small portion of the
stroke. To increase the effectiveness of the pump, the valve is
moved into its equalizing position before the piston begins its
return stroke. The air under pressure is then transferred to the
other side of the piston, where it is compressed and is discharged
through the valves at the top of the cylinder. By this means the
suction side of the piston is effective throughout its entire stroke.
Circulating Pumps. — While reciprocating pumps are used to a
very large extent in condenser operation as dry- and as wet-air

Single stage centrifugal pump.

pumps, centrifugal pumps are generally used as circulating
pumps supplying cooling water to surface condensers. Centrifu-
gal pumps are also used as hot-well pumps.

Fig. 144 illustrates a section through a single stage centrifugal
pump. It consists of a rotary impeller, into which the water is
drawn and, because of the centrifugal force, leaves the tips of the
rotor at high velocity. The casing of the pump guides the water
from the propeller to the discharge outlet. No valves are
required in this type of pump.

The single stage pump is limited in its application to compara-

17G STEAM AND GAS POWER ENGINEERING

tively low heads or pressures. For high heads a greater number
of stages are used. In these the water is discharged from one
rotor to the next, each rotor acting as a booster. However,
condenser operation requires comparatively low heads and the
single stage pump will be found sufficient for most installations.

Cooling Ponds and Cooling Towers

Reclaiming Cooling Water. — The quantity of cooling water
required to condense steam varies from 30 to 70 pounds for each
pound of steam condensed. In many plants this water, after
passing through the condenser, is wasted; hence a continuous
supply of fresh water is required. In localities where water is
plentiful and its cost is low, this practice may be correct, but
many plants are handicapped on account of the scarcity or
high cost of water. In such cases the saving of cooling water is
an important problem. Several methods have been developed
to cool the condenser circulating water so that it can be used
repeatedly.

The means for reclaiming the water usually adopted at the
present time depends upon the cooling effect derived from the
evaporation of water. Air has the property of evaporating and
absorbing water. The amount of water absorbed depends upon
the condition of the air, while the rate of evaporation depends
upon the velocity and degree of contact between the air and
water. As an illustration, air at a temperature of 90°F. and 50
per cent, humidity, which signifies that the air is only one-half
saturated, would be theoretically capable of cooling condenser
circulating water to 75°F., or 15° below the temperature of the
atmosphere. On the other hand, on a wet rainy day, when the
air is saturated with moisture, little or no cooling effect could
be produced by evaporation, for the air contains nearly as much
water as it will absorb.

The following three systems are used for reclaiming condenser
circulating water: cooling ponds, spray ponds, and cooling
towers.

When reclaiming circulating water by any of the above
methods, an allowance of 2 to 8 per cent, should be made for
evaporation.

ENGINE AND TURBINE AUXILIARIES 177

Cooling Ponds. — Cooling ponds or tanks depend for their
cooling effect upon the exposure of a comparatively large area
of water to the air. In these the water is cooled partly by radia-
tion but principally by evaporation. The cooling is dependent
upon the surface exposed and consequently cooling ponds are
usually shallow, but spread over a considerable area. The hot
water from the condenser enters the pond at one point, and is
cooled by surface evaporation when it reaches the intake point
to the condenser.

Cooling ponds are very simple, but are open to the objection
that the evaporation is slow. Furthermore they may freeze
in winter, and thus cut off the supply of condensing water.

Spray Ponds. — In this system the hot water from the condenser
is cooled by spraying it into the air so that it falls in a thin mist
into the basin or pond below. The spray brings the air and water'
into intimate contact, exposes a large amount of water surface
to the air, and consequently produces a large cooling effect in a
comparatively small space. The water is pumped from the
condenser and is forced through the spray nozzles under pres-
sure. Sufficient cooling is effected by the fine spray so that the
water may be immediately returned to the condenser.

When compared with the cooling pond, the spray pond occupies .
less space. A pond depending upon natural evaporation would
be approximately 50 times as large as a spray pond for the same
cooling capacity. In cases where the cooling effect is not suffi-
cient in a single spraying, the water may be forced through the
nozzles a second time, thus securing a double-cooling effect.

Cooling Towers. — A cooling tower consists of a wooden, sheet
iron, or concrete chamber that is filled with mats made of steel
wire, wooden slats, or tile. Hot water from the condenser is
elevated to the top of the tower and is distributed evenly over
the top surface. The water in descending is retarded, is broken
up by the mats, and is thus brought in intimate contact with the
air that ascends through the tower.

The method of supplying the air to cooling towers gives rise
to three classifications: open towers or atmospheric coolers;
natural-draft towers; forced-draft towers.

The open tower is the simplest, although it requires larger
ground space. The mats are supported on a tower of open grill
12

178 STEAM AND GAS POWER ENGINEERING

work, so arranged that the descending water will be subjected
to the slightest wind. This type of tower has proved successful
in localities where the climate is dry and where winds prevail.

Fig. 145. — Forced-draft cooling tower.

The natural-draft or flue tower depends for its cooling upon the
flow of air, which results when the air within the tower and that
without are at different densities. The air within the tower

ENGINE AND TURBINE AUXILIARIES

179

will always be the lighter because of its higher temperature and
because of the greater amount of moisture it contains. The
necessary velocity of air through the tower can be made as de-
sired by proportioning the height of the tower. The natural-
draft tower is entirely enclosed, except at top and bottom. The
condenser water is distributed at the top, while the air becoming
heated is displaced by the colder air which enters at the base of
the tower. These towers are suitable for locations where space
requirements would prohibit the open or atmospheric tower.

The forced-draft tower lends itself to practically all locations
and conditions. Fig. 145 illustrates a sectional view of a forced-
draft tower. This type of tower is operated in the same manner
as other cooling towers, but a fan is used to create the flow of air
through the descending water.

These towers are light and compact, requiring about one-fifth
the space occupied by a tower of the natural-draft type. They-
are entirely independent of the natural circulation of the air,
and are consequently more reliable. The A

power required to operate a forced-draft
cooling tower will vary from 2% to 4 per
cent, of the total power generated by the
main units.

Sepabators

Steam Separators. — The function of
a steam separator is to protect engines
and turbines from the dangerous results
that might occur if large quantities of
water or grit enter them. When the
boiler is improperly proportioned or
when it is forced above its rating, there
is a possibility of large amounts of water
being carried over with the steam. The
condensation that occurs in long pipe
lines adds to the water in the steam.

Fig

1 46. — Steam
separator.

The steam separator
automatically separates the water from the steam, thus pro-
tecting the cylinder, and at the same time promotes lubrica-
tion by preventing the washing action that results when wet
steam is used in the engine cylinder.

180 STEAM AND GAS POWER ENGINEERING

Fig. 146 illustrates one type of steam separator. The flow
of the steam in passing through the separator is interrupted by
corrugated plates. The momentum of the heavier particles of
water causes them to be thrown out, and they adhere to the sur-
face of the baffle. The separated water then flows by gravity
to the trap or receiver below, from which it is drained.

Separators are made in various sizes, depending upon the size
of the pipe to which they are to be attached. They may be
used on vertical, horizontal, or angle pipes. Special separators,
known as the receiver type, with an extra large water storing
capacity are made and are usually installed in plants having long
pipe systems, where there is a possibility of large quantities of
water suddenly passing through with the steam.

The separator should be placed
as close to the steam chest of the
engine as possible. The receiver
type of separator is preferable if
the engine load is intermittent or
fluctuates rapidly.

Exhaust-steam and Oil Separa-
tors. — Exhaust-steam separators
are constructed on the same prin-
ciples as steam separators, but
their function is to remove oil that
may be contained in the exhaust
steam. The use of a good oil
separator between the engine and
the condenser will eliminate the oil
from the condensate, thus making
it satisfactory as boiler feed water.
In the case of surface condensers,
oil separators prevent the fouling
of the condenser tubes by the oil
which would lower the efficiency of the condenser if allowed to
accumulate.

In exhaust steam heating the oil separator is used to remove the
oil from the steam before it enters the heating system. Oil
in the steam would coat the inner surface of radiators with a

Fig. 147. — Exhaust head.

ENGINE AND TURBINE AUXILIARIES 181

thin layer of grease which would soon impair the amount of heat
transmitted through them.

In the use of feed-water heaters, the oil separator may be
entirely independent and separately installed, but in most
cases, it is made a part of the heater itself.

In plants where low pressure turbines are utilized, an oil
separator is placed between the engine and the turbine. The
moisture and oil are thus removed from the exhaust steam
before it enters the turbine.

Exhaust Heads. — Fig. 147 illustrates a section through an
exhaust head. This device is used to prevent the deposit of any
moisture or oil upon roofs and side walks when the exhaust from
an engine is allowed to escape to the atmosphere. Exhaust
heads are attached in a vertical position at the end of the atmos-
pheric exhaust pipe. Their principle of operation, like that of
the separator, depends upon the changing of the course of the
steam. The moisture and oil thrown out by centrifugal force
collect at the bottom of the head and are drained to waste.

Problems

1. Compare the volumes of steam and of water at atmospheric pressure.

2. Compare the volume of one pound of steam at atmospheric pressure
with the volumes at 26 inches vacuum, 28 inches vacuum, and 29 inches
vacuum.

3. A condenser gage registers 28.5 inches of mercury. The barometer
registers 29.35 inches of mercury. What is the absolute pressure of the air
in pounds per square inch? What is the absolute pressure in the condenser
in pounds per square inch?

4. Make a sketch of the exhaust piping between an engine and a condenser
showing the location of the atmospheric relief valve.

. CHAPTER X
STEAM POWER PLANT TESTING

General Rules. — The chief object in the testing of power plant
equipment is to secure data from which the ccst of operation may
be calculated. Tests are also carried on for the purpose of com-
paring actual with guaranteed results as to capacity and efficiency
of the complete power plant or of the separate parts. The
effect of different conditions of operation or of changes in design
can also be determined by test.

The test of a power plant is essentially a test of each of the
various main parts; it is a combined test of the steam boiler,
of the steam engine or turbine, and of the other power plant
equipment.

The testing of a power plant includes the measurement of
certain conditions which are important economically in the opera-
tion of the plant. This may be done by the reading of various
appliances at specified intervals when the test is in progress or
by the use of special instruments of the recording type. The
recording instrument gives a continuous record which is often
desirable in studying the daily operation of the plant. In reality,
with recording instruments, the plant is continuously under test
and any variation that may occur from day to day is indicated
graphically. The economy test consists, in general, in the
measurement of the amount of heat supplied and the amount of
energy that has been transformed into useful work.

In testing a boiler, the amount of coal fired would give a direct
measure of the heat supplied. To find the amount of energy
transformed, the weight of the water evaporated, the quality
of the steam generated, the pressure in the boiler, and the tem-
perature of the entering feed water must be measured. To assist
in determining the extent of the losses in a boiler plant, such
readings as the temperature of the flue gases, the draft at various
points in the boiler, and the analysis of the flue gases are usually
taken.

182

STEAM POWER PLANT TESTING 183

The testing of the engine or turbine consists in measuring the
weight of the steam supplied together with its quality and pres-
sure at the throttle as well as the pressure of the exhaust; from
this data the heat supplied to the motor may be calculated. The
delivered power is measured by a Prony brake, an electrical
generator, or some other form of dynamometer. As in the case
of the boiler, .many other readings are taken during the test.
These consist of such data as indicator cards, in the case of re-
ciprocating steam engines; the amount of condensing water, and
various temperatures at the condenser.

Preparing for the Test. — A thorough examination should be
made of the physical condition of all parts of the plant including
boilers, furnaces, settings, engine cylinders, piping, valves,
etc. Prior to the test any defects that may make the results of
the test unfavorable should first be remedied. In boilers, for
example, any abnormal leakage found at the tubes, rivets, or
metal joints should be repaired. All leakage from blow-offs,
drips, etc., or through any steam or water connections which
might affect the results should be prevented. In preparing for
the test the dimensions of the principal parts of apparatus to be
tested should be taken and recorded. Before the test is started
it is important that the apparatus to be tested has been in
operation a sufficient length of time to attain proper operating
conditions.

Starting and Stopping the Test. — In a plant operating con-
tinuously day and night the time for starting and stopping the
test of a boiler should follow the regular period of cleaning
the fires. The fires should be quickly cleaned and then burned
low. When this condition has been reached the time should be
noted as the starting time, and the thickness of the coal bed,
the water level in the boiler, and the steam pressure should be
noted. At the close of the test following a regular cleaning, the
fires should again be burned low, and when this condition has
become the same as that observed at the beginning, the water
level and steam pressure also being the same, the time is noted
and the test is stopped.

Weighing the Fuel. — The approved method of weighing the
fuel burned in a specified interval of time is by the use of ordinary
platform scales. If accurate results are to be secured it is not

184 STEAM AND GAS POWER ENGINEERING

recommended to weigh the fuel in a wheelbarrow or similar
conveyance full of coal and assume that all other loads brought
into the plant weigh the same; it is also inaccurate to base the
weight of the fuel upon the number of strokes of the plunger
in certain types of stokers. Even in the use of scales care must
be taken to test their reliability by calibrating them with stan-
dard weights. In case the use of scales is impracticable, sacks
or bags containing a known weight of coal, as measured by a
platform scale, may be used to good advantage.

Large plants in which coal handling machinery has been
installed use weighing hoppers to measure the coal fed to the
boilers. As usually installed the weighing hopper is placed be-
tween the main storage bunker in the loft of the plant and the
stoker hoppers below. Coal from the main bunker passes first
to the weighing hopper. After being weighed the coal is dis-
tributed to the stoker hoppers. The weighing hopper travels
upon a special overhead track which makes it possible for one
weighing hopper to serve several boilers. The scale beams and
levers extend downward so that the poise on the weighing beam
is read from the boiler room floor.

Weighing the Feed Water. — The most satisfactory method
for weighing the feed water, which is the weight of the water
evaporated by the boiler, consists in the use of one or more tanks

each placed upon platform scales.
These are elevated a sufficient dis-
tance above the floor to empty into
a receiving tank, which is in turn
connected to the boiler feed pump.
When only one tank is available the
receiving tank should be of sufficient
size to afford a reserve supply to
the pump while the weighing tank
is filling.

A great many types of water meters are sold commercially and
are often used in measuring the feed water. To insure a fair
degree of accuracy the meter should be calibrated before and
after the test under the identical conditions it is required to
operate.

The measurement of large quantities of hot water is usually

Fig. 148. — Triangular weir.

STEAM POWER PLANT TESTING

185

accomplished by the use of special types of water meters, weirs,
orifices, or automatic water weighers.

Fig. 148 illustrates a weir with a triangular notch, although
many other forms of notches may be used. The amount of

Pipes to Manometer

Inlet

Outlet

Fig. 149. — Venturi meter.

water discharged is dependent upon the distance or head above the
bottom of the weir.

The Venturi meter is an arrangement of piping in which there is
a gradual narrowing of the section followed by a gradual enlarge-
ment. Fig. 149 illustrates this type of meter. Tubes entering
the meter at the sections shown and attached to
the manometer are used in measuring the quan-
tity of water delivered.

Dratt Gages. — The simplest form of draft
gage is the U-tube or manometer, illustrated in
Fig. 150. For the measurement of draft the
tube is filled with water and is connected at
"A" by means of tubing to the point where the
pressure is to be measured. The amount of
pressure will be indicated by the difference in
the level of the liquid and may be measured in
inches of water.

For the measurement of slight pressures an
inclined tube, as illustrated in Fig. 151, may be FlG- 15°-

7 ° ' J or manometer.

used. The bottle B to which the inclined tube

CD is attached is filled with water. The outer end of the inclined

tube is attached to the chamber in which the pressure is to be

-U-tube

186 STEAM AND GAS POWER ENGINEERING

measured. The pressure is measured as with the U-tube (Fig.
150), but by the use of the inclined tube the movement of one
inch in a vertical scale is magnified.

Fig. 151. — Inclined tube manometer.

Temperature Measurement. — Temperatures are usually
measured by means of one of the following types of thermometers :
mercurial thermometers; electrical resistance thermometers;
mechanical pyrometers; thermoelectric pyrometers.

The ordinary mercury in glass thermometer is commonly used
for temperatures less than 500°F.; above 500° special nitrogen
filled glass thermometers must be used.

Fig. 152. — Diagram of the thermoelectric method of temperature measurement.

Electrical resistance thermometers are based upon the prin-
ciple that the resistance of certain metals changes with change of
temperature. The thermometer element is constructed of some
metal, like platinum, and the variation of resistance measured
by a Wheatstone bridge.

STEAM POWER PLANT TESTING 187

Mechanical pyrometers consist of two metal-rods whose rate
of expansion differ. The rods are connected through gears and
levers to a pointer which rotates over the dial graduated in
degrees of temperature.

Thermoelectric pyrometers are based upon the principle that
an electromotive force is produced when two wires of different
metals are joined and heated. Fig. 152 illustrates a thermoelec-
tric pyrometer. T is a porcelain tube which holds the two dis-
similar metal wires and which is placed at the point where the
temperature is to be read. M is a meter for measuring the im-
pressed voltage; it is provided with a scale calibrated in degrees.

Measuring the Weight of Steam. — The most satisfactory
method of weighing the amount of steam consumed by the
engines or turbines is by the use of platform scales and surface
condensers. This method utilizes two scales and two tanks

Trailing Set

Leading Set
Fig. 153. — Steam flow meter nozzle.

which are alternately filled with condensed steam from the con-
denser, weighed, and emptied.

Various forms of steam meters may be employed for measuring
the steam, provided such meters are properly calibrated under
the conditions to which they will be subjected when in use.

Figs. 153 and 154 illustrate one type of steam meter. This
instrument measures the steam flow by recording the velocity.
The nozzle plug (Fig. 153) is inserted into the steam pipe, and
in this plug are two sets of holes which communicate through
separate pipes to the meter (Fig. 154). The leading set of holes
is subjected to the velocity and the pressure of the steam while
the trailing set is subjected only to the pressure. Their differ-
ence records the effect caused by velocity.

The recording meter is essentially a mercury U-tube or mano-
meter. A difference of pressure in the nozzle plug causes a
difference in height of the mercury. Change in the position of

188 STEAM AND GAS POWER ENGINEERING

Fig. 155. — The Alden water brake.

STEAM POWER PLANT TESTING

189

the mercury column is measured by a small float suspended from
pulleys which in turn move the indicating needle.

Measurement of Power. — One of the simplest means of
measuring the power delivered by a
small motor is by the application of a
Prony Brake to the rim of the wheel as
explained in Chapter VII. For motors
of large capacity or operating at high
speeds some other type of dynamometer
or an electrical generator must be used.

Another type of brake for absorbing
and measuring power is some form of
water friction brake. Fig. 155 illustrates
one type of water brake. It consists of
a disk A which is connected to the shaft
S transmitting the power. The disk
revolves in a copper chamber filled with
oil while cooling is effected by the
circulation of water around the outer
surface of the copper chamber. The
friction of the oil producing the braking
effect is transmitted to the arm P where
it is measured as in the Prony brake. FlG- 156-~ Speed counter.

Measurement of Speed. — For determining the speed of an
engine shaft in revolutions per minute a speed indicator Fig.
156 and watch, or a tachometer Fig. 157 is used. The tachom-

Fig. 157. — Tachometer.

eter is more convenient, as it indicates on the dial the revolu-
tions per minute.

Indicator and Calorimeters. — Steam engine indicators, steam
calorimeters, coal calorimeters, and other important instru-

190 STEAM AND GAS POWER ENGINEERING

ments used in power plant testing were explained in previous
chapters.

A. S. M. E. Code. — Complete and more detailed instructions
concerning the testing of steam power plants and power plant
equipment will be found in the Rules for Conducting Performance
Tests of Power Plant Apparatus, published by the American
Society of Mechanical Engineers.

Problems

1. Examine some water meter and explain, using clear sketches, how the
meter works.

2. Explain the principles upon which the construction of recording in-
struments are built.

3. From the A. S. M. E. Power Plant Code compile a table showing the
principal data to be taken of a test on a non-condensing steam power plant.

CHAPTER XI
INTERNAL COMBUSTION ENGINES

The internal combustion engine, commonly called a gas engine,
differs from the steam engine, which is an external combustion
motor, in that the transformation of the heat energy of the fuel
into work takes place within the engine cylinder.

History. — The earliest internal combustion engine was the
gunpowder engine invented by Huyghens in 1680. In the
Huyghens engine a charge of gunpowder was introduced into a
vertical cylinder filled with air and exploded ; the products of com-
bustion were driven out of the cylinder through valves, and the
piston, which was at the end of the stroke, was forced down by
the atmospheric pressure into the vacuum thus formed.

The first attempt to produce power from an inflammable
gas, manufactured by the distillation of coal or oil, was made
by Barber in 1791. The Barber motor included an air pump and
a compressor which forced the inflammable gas and air into a
vessel, where the mixture was ignited; the burning mixture issuing
from the vessel impinged against the vanes of a paddle wheel and
produced the rotation of a shaft connected to the machinery to be
driven. The first reciprocating engine using an inflammable gas
was invented by Street in 1794.

Lebon in 1801 first suggested the compression of the mixture
of gas and air before ignition. This was applied by Barnet in
1838.

From 1801 to 1860 many efforts were made to produce a prac-
tical internal combustion engine. Several types of free piston
engines were developed during this pericd in which the explosion
of a mixture of gas and air was utilized in moving upward in a
vertical cylinder a piston which was free from the connecting
rod. The work was done on the return stroke by the pressure
of the atmosphere forcing the piston down, the piston rod on its
downward stroke producing rotary motion through a rack

191

192 STEAM AND GAS POWER ENGINEERING

meshing with a spur pinion and connected by a ratchet and pawl
to the driving shaft.

The Lenoir engine, which was invented about 1860, was the
first internal combustion engine to be used commercially to any
extent for producing power. The Lenoir engine was a horizontal
double-acting reciprocating motor. The mixture of the fuel and
air was drawn into one end of the engine cylinder during the first
part of the stroke, the inlet valve being closed at about one-half
of the stroke, when the mixture was ignited. The explosion
(rapid combustion) of the mixture forced the piston to the end
of the stroke. Near the end of the stroke the exhaust valve
opened, and the products of combustion were expelled during
the return stroke. The same operation took place at both ends
of the cylinder, the energy stored in the flywheel driving the
piston forward during the suction part of its stroke. The
Lenoir engine, similar to the steam engine, had two working
strokes during each revolution, but was superseded by engines
working on the Otto or Diesel cycles, which have only one work-
ing stroke for every two revolutions of the crank shaft.

The Otto Internal Combustion Engine Cycle. — The majority
of modern commercial internal combustion engines operate
upon the Otto internal combustion engine cycle, which was sug-
gested by Beau de Rochas in 1862, and which was made a prac-
tical success by Nicholas A. Otto in 1878. The term engine cycle
is applied to the series of events which are essential for carrying
out the transformation of heat into work. The Otto internal
combustion engine cycle requires four strokes of the piston and
comprises five events, which are: suction, compression, igni-
tion, expansion, and exhaust.

The action of an internal combustion engine working on the
four-stroke Otto cycle is illustrated in Figs. 158 to 162.

1. Suction of the mixture of air and gas through the inlet valve
takes place during the complete outward stroke of the piston,
the exhaust valve being closed. This stroke of the piston is
called the suction stroke and is illustrated in Fig. 158.

2. On the return of the piston, shown in Fig. 159, both the inlet
and exhaust valves remain closed and the mixture is compressed
between the piston and the closed end of the cylinder. This is
called the compression stroke. Just before the compression

INTERNAL COMBUSTION ENGINES

193

stroke of the piston is completed, the compressed mixture is
ignited by a spark (Fig. 160) and rapid combustion or explosion
takes place.

3. The increased pressure within the cylinder due to the rapid
combustion of the mixture drives the piston on its second forward
stroke, which is the power stroke (Fig. 161). This power stroke,
or working stroke, is the only stroke in the cycle during which
power is generated. Both valves remain closed until the end
of the power stroke, when the exhaust valve opens and provides
communication between the cylinder and the atmosphere.

Inlet Valve. |

£s??5a^3__^-*<

Spark Plug ■■■>*}

if 5§

@-~~T~~1&

'xhaust Valve' \

Suction

Inlet Valve-.
Spark Plug ~x
Exhaust Valve^

Inlet Valve-.

I J

^■/■/.«#-„. ^*

Spark Plug ■■■>*

|J|P^--€2

Exhaust Valve"

Ignition

Inlet Valve;,

Spark Plug^

Exhaust Valve

Exhaust

Expansion
Figs. 158-162.— The events in the Otto Cycle.

4. The exhaust valve remains open during the fourth stroke
called the exhaust stroke, Fig. 162, during which the burned
gases are driven out from the cylinder by the return of the piston.

The simplest type of internal combustion engine operating on
the Otto four -stroke cycle is the gasoline engine which is illus-
trated in Fig. 163. The fuel from the liquid fuel tank T is
supplied to the mixing valve or carburetor through the fuel
regulating valve G. The air, through the air pipe A, enters
the same carburetor and is thoroughly mixed with the fuel. The
mixture of air and vaporized fuel enters the engine cylinder C
through the inlet valve V as the piston P moves on the suction
stroke. The mixture is then compressed, and ignited by an
electric spark produced at the spark plug Z, by current fur-
nished from the battery B. The ignition of the mixture is
followed by the power stroke. The reciprocating motion of the
13

194 STEAM AND GAS POWER ENGINEERING

piston P is communicated, through the connecting rod R
to the crank N, and is changed into rotary motion at the crank
shaft S. The crankshaft S, while driving the machinery to
which it is connected, also turns the valve gear shaft, sometimes
called the two-to-one shaft, through the gears X and Y.
The gear Y turns once for every two revolutions of the crank,
and near the end of the power stroke opens the exhaust valve
E through the rod D pivoted at 0.

Fig. 163. — Parts of a gasoline engine.

In larger engines the valve gear shaft also opens and closes
the admission valve V and operates the fuel pump and ignition
system. As the temperatures resulting from the ignition of the
explosive mixture is usually over 2000 °F., some method of
cooling the walls of the cylinder must be used in order to facili-
tate lubrication, to prevent the moving parts from being twisted
out of shape, and to avoid the ignition of the explosive mixture
at the wrong time of the cycle. One method of cooling gas
engines is to jacket the cylinder J, that is, to construct a
double-walled cylinder and circulate water between the two walls,
through the jacket space. The base U supports the various
parts of the engine; the flywheel W carries the engine through
the idle strokes. Besides the above details, every gas engine is
usually provided with lubricators L for the cylinder and bear-
ings, and with a governor for keeping the speed constant at
variable loads.

INTERNAL COMBUSTION ENGINES

195

An indicator diagram, taken from a four-stroke cycle internal
combustion engine, using gasoline as fuel, is illustrated in Fig.
164. IB is the suction stroke, BC the compression stroke,
CD shows the ignition event, DE the power stroke, and EI is the
exhaust stroke. The direction of motion of the piston during
every stroke is illustrated in each case by arrows. Lines AF
and AG were added to the indicator diagram; AF is the atmos-
pheric line, while AG is the line of pressures. From Fig. 164 it
will be noticed that part of the suction stroke occurs at a pres-
sure lower than atmospheric. The reason for this is that a
slight vacuum is created in the cylinder by the piston moving
away from the cylinder head. The vacuum helps to draw the
mixture of fuel and air into the cylinder.

Suction Stroke
Fig. 164. — Gas-engine indicator card.

Modern internal combustion engines, operating on the Otto
four-stroke cycle, will convert 14 to 30 per cent, of the heat avail-
able in the fuel into work. The Lenoir engines, in which the
mixture was not compressed previous to ignition, converted only
about four per cent, of the heat available in the fuel into work.

The efficiency of engines operating on the Otto cycle depends
upon the pressure to which the mixture of fuel and air is
compressed before ignition. Theoretically, the greater the com-
pression pressure, the better is the economy. Practical consid-
erations and the danger of preignition limit the compression
pressures for various fuels to the following values in pounds
per square inch: Gasoline 60 to 90 pounds, kerosene 50 to 80
pounds, alcohol 120 to 180 pounds, natural gas 80 to 120

196 STEAM AND GAS POWER ENGINEERING

pounds, producer gas 120 to 160 pounds, blast furnace gas
120 to 190 pounds.

From the above values of practical compression pressures it is
evident that with fuels high in hydrocarbons lower compression
pressures should be employed than with fuels which are low in
these constituents.

The Two-stroke Cycle Engine. — The internal combustion
engine working on the four-stroke cycle requires two complete

revolutions of the crankshaft, or four
strokes of the piston to produce one
power stroke. The other three are only
idle strokes, but power is required to
move the piston through these strokes,
and this has to be furnished by storing
extra momentum in heavy flywheels.
The Otto cycle can be modified so that
the five events can be carried out during
only two strokes of the piston by pre-
compressing the mixture of fuel and
air in a separate chamber, and by
having the events of expansion, ex-
haust, and admission occur during the
same stroke of the piston. In large
two-stroke cycle engines the air and
fuel for the mixture are compressed and
delivered separately by auxiliary pumps
driven from the main engine shaft,
the mixture in the case of small two-
stroke cycle engines is accomplished by having a tightly closed
crank case, or by closing the crank end of the cylinder and by
providing a stuffing box for the piston rod.

The main features of the two-stroke cycle internal com-
bustion engine are illustrated in Fig. 165. On the upward stroke
of the piston P, a partial vacuum is created in the crank case C,
and the explosive mixture of fuel and air is drawn in through a
valve at A. At the same time a mixture previously taken into
the upper end of the cylinder W is compressed. Near the end of
the compression stroke, the mixture is fired from a spark pro-
duced at the spark plug S. The explosion of the mixture drives

Fig. 165. — Small two-stroke
cycle engine.

The

precompression

INTERNAL COMBUSTION ENGINES 197

the piston on its downward or working stroke. The piston
descending compresses the mixture in the crank case to about 6
or 8 pounds above atmospheric, the admission valve at A being
closed as soon as the pressure in the crank case exceeds atmos-
pheric. When the piston is very near the end of its downward
stroke, it uncovers the exhaust port at E and allows the burned
gases to escape into the atmosphere. The piston continuing on
its downward stroke next uncovers the port at 7, allowing the
slightly compressed mixture in the crank case C to rush into the
working part of the cylinder W. Thus two full strokes of the
piston complete one cycle.

The distinctive feature of the two-stroke cycle engine is the
absence of valves. The transfer port I from the crank case
C to the working part of the cylinder W, as well as the exhaust
port E, are opened and closed by the piston.

Large two-stroke cycle engines are often made double-
acting and have the same number of power impulses per revolu-
tion as the single-cylinder steam engine. The proper amounts of
gas and air are delivered to each end of the piston at the correct
time by auxiliary pumps. An admission valve is provided at
each end of the cylinder. The exhaust takes place through
ports near the middle of the cylinder, which are uncovered by
the piston at the end of each working stroke.

To offset the advantages resulting from fewer valves, less
weight, and greater frequency in working strokes, the two-stroke
cycle engine is usually less economical in fuel consumption and is
not as reliable as is the four-stroke cycle engine. As the inlet
port I (Fig. 165) is opened while the exhaust of the gases takes
place at E, there is always some chance that part of the fresh
mixture will pass out through the exhaust port. Closing the
exhaust port too soon will cause a decrease in power and effi-
ciency, on account of the mixing of the inert burned gases with
the fresh mixture. By carefully proportioning the size and
location of the ports, and by providing the piston with a lip at
L (Fig. 165) to direct the incoming mixture toward the cylinder
head, the above losses may be decreased. In large two-stroke
cycle engines an effort is made to eliminate the above loss by
forcing a current of air through the cylinder by the air pump, while
the exhaust port remains open. In any case the scavenging of

198 STEAM AND GAS POWER ENGINEERING

the cylinder of the waste gases is not as thorough in the two-
stroke cycle as in the four-stroke cycle engine, where one com-
plete stroke of the piston is allowed for the removal of the exhaust
gases. The four-stroke cycle engine has also the advantage of
wider use and longer period of development.

The Diesel Internal Combustion Engine Cycle. — The Diesel
engine cycle is applied only to oil engines. This cycle, similar
to the Otto, comprises five events: suction, compression, ignition,
expansion, and exhaust. In the Otto internal combustion
engine cycle, air is mixed with the fuel in definite proportions
and the combustible mixture is subjected to the process of com-
pression. In the Diesel engine cycle only air is admitted to the
cylinder during the suction stroke, so that compression pressures
as high as desired are permitted without the danger from pre-
ignition. The compression pressures used with Diesel engines

Fig. 166. — Indicator card from Diesel oil engine.

vary from 450 to 500 pounds per square inch. The higher
compression pressure limit in this case is not dependent upon the
composition of the mixture within the cylinder but upon con-
struction details. At the end of the compression stroke of the
Diesel engine piston, oil fuel is injected into the cylinder. The
oil enters the cylinder in the form of a fine spray, mixes with
the highly compressed air, which is at a temperature of about
1000°F., is ignited and burns at nearly constant pressure. The
duration of the oil injection is governed by the load upon the
engine. This period of oil injection, as well as the compression
pressure, influences the fuel economy of a Diesel engine.

An indicator diagram taken from a Diesel oil engine is shown
in Fig. 166. Air is drawn into the cylinder during the suction
stroke A B. The return of the piston compresses the air to a
pressure of about 470 pounds per square inch during the stroke

INTERNAL COMBUSTION ENGINES

199

BC. The fuel-oil is then gradually introduced by means of an
oil pump, to an amount depending upon the load, and burns

JQieiSBion VilTe

Cooling
JYater

Fig. 167. — Cross-section of American Diesel engine.

during CD, the first part of the third stroke. This is followed
by the expansion of the gases within the cylinder to the end

200 STEAM AND GAS POWER ENGINEERING

of the third stroke along DE. At E the exhaust valve opens
and the burned gases are exhausted from the cylinder during the
fourth stroke EA .

A section through a Diesel engine is illustrated in Fig. 167.
Internal combustion engines operating on the Diesel cycle are
more expensive to build and require better supervision than
engines operating on the Otto cycle, but give better fuel economy
and are capable of operating with the very cheapest liquid
fuels. Under good conditions Diesel engines will convert
more than 30 per cent, of the heat in the fuel into work, while oil
engines operating on the Otto cycle will usually convert only
about 20 per cent.

Details of Internal Combustion Engines. — The fundamental
details of an internal combuston engine are :

1. The Fuel System. — -This includes fuel storage, piping from
the storage to the engine, and a device for preparing the mixture
of air and fuel. In order to form an explosive mixture, air must
be mixed in certain definite proportions with the fuel, and this
can be accomplished only when the fuel is in the gaseous state,
or is a mist of liquid fuel easily vaporized at ordinary tempera-
tures. Thus the essential difference between internal combus-
tion engines using the various fuels is in the construction of the
device for preparing the fuel before it enters the engine cylinder.
If the fuel is initially a gas, only a mixing valve is necessary to
control the proportions of fuel and air. Fuels which are in the
liquid state must be vaporized and mixed with air to form an
explosive charge. The devices required for preparing liquid
fuels depend on the character of the fuel, a heavy fuel requiring
heat, while a volatile fuel, such as gasoline, is easily vaporized at
ordinary temperatures by being broken up into fine mist. When
an engine uses a volatile liquid fuel, like gasoline, the fuel is
vaporized and mixed with the correct proportion of air in a
device called a carburetor. Various types of carburetors will
be illustrated and explained in Chapter XIII.

2. A Jacketed Cylinder and Piston. — -In small engines only the
cylinder and cylinder head must be cooled. In large engines it
becomes necessary to cool also the piston and the exhaust valve
to prevent overheating of the metal. The methods used in
cooling gas engine cylinders are illustrated in Figs. 168 and 169.

INTERNAL COMBUSTION ENGINES

201

An air-cooled cylinder is illustrated in Fig. 168. This cylinder
is cast with webs, and air is circulated by means of a fan driven
by the engine. The air cooling system has not been found prac-
tical for stationary engines above 5 horsepower, as there is
no positive temperature control with this system. This lack of
temperature control results in the decomposition of the cylinder

Fig. 168. — Air-cooled cylinder.

oil and in carbon deposits on the piston and cylinder walls. t
Considerable success has been attained with air cooled motors
for automobiles and motorcycles.

The cooling of engine cylinder walls by means of water is the
most common method. In this case the cylinder barrel or the
cylinder barrel and cylinder head are jacketed; that is, they are
built with double walls and water is circulated through the space

202 STEAM AND GAS POWER ENGINEERING

between the walls. The cylinder wall or barrel is cast separate
from the jacket, except in small engines, where the cylinder
barrel and jacket walls are cast together. In order to definitely
control the temperature of the water jacket, the forced system

of water circulation (Fig. 169) is generally used for stationary
engines.

Cylinders for internal combustion engines are single acting
and are usually fastened to the frame at one end only, to allow
for the free expansion of the metal.

INTERNAL COMBUSTION ENGINES 203

The trunk type of piston (Fig. 169) is most commonly used,
for it acts not only as a piston but also as a cross-head. The
piston is usually provided with three or more rings, as it is very
important that leakage past the piston be eliminated.

3. Inlet and Exhaust Valves. — With the exception of some
automobile motors, which are equipped with sleeve valves,
valves for internal combustion engines are generally of the pop-
pet or mushroom type, with conical seats (Fig. 169).

The inlet valves are not jacketed, as they are cooled by the
incoming mixture during the suction stroke. Exhaust valves
must be cooled in all except very small engines, as these valves
are in contact with very hot gases for a considerable period of
time.

Small engines are sometimes provided with inlet valves which
are automatically operated by the suction of the piston, being
held to their seats by weak springs. Automatically operated
valves are uncertain in their action and are seldom used. Mechan-
ically operated valves are positively controlled and are generally
used both for inlet and for exhaust valves.

The valves are operated by means of cams or eccentrics from
an auxiliary shaft which is driven by means of gears from the
main engine shaft. In the four-stroke cycle engine the auxiliary
shaft is operated at one-half the speed of the main shaft. In
small engines the valves are actuated by cams, but in large engines
eccentrics are employed for this purpose.

4. A mechanism for changing the reciprocating motion of the
piston into rotation at the crank shaft. This change is accom-
plished by means of a connecting rod and crank.

5. Ignition System. — Ignition of the mixture in modern inter-
nal combustion engines is accomplished either by a spark, or
automatically by the high compression to which either the air or
the mixture is subjected in the engine cylinder. The subject of *
ignition will be treated in detail in Chapter XIII.

6. A governor for keeping the speed constant as the power
developed by the engine varies. The governing mechanism is
operated by the speed variations of the engine and the speed
control is accomplished either by the hit-or-miss, or by the throt-
tling methods as will be explained later.

7. A flywheel for carrying the engine through the idle strokes.

204 STEAM AND GAS POWER ENGINEERING

8. Engine frame and bearings for supporting the various
parts of the engine.

9. Foundations for the engine and auxiliaries.

10. Lubricating system which includes grease cups, sight-
feed oilers, and positive force feed oilers. For high speed motors
the forced-flooded system of lubrication is commonly empk^ed.
In this system a pump forces oil to the various bearings, keeping
them flooded with oil at all times.

Oil Engines. — The first successful oil engines were gasoline
engines, as gasoline is the lightest of all commercial hydrocarbons

Fig. 170. — Hot-bulb oil engine.

and is easily vaporized at ordinary atmospheric temperatures.
Gasoline engines consume one-eighth to one-tenth of a gallon of
gasoline per brake horsepower per hour. Gasoline is the most
important fuel for small stationary and portable engines; also
for light-weight high speed engines, such as are used on auto-
mobiles and aeroplanes.

The ordinary gasoline engines (Fig. 163) which employ electric
ignition cannot operate satisfactorily on heavy petroleum fuels.
The type of hot bulb engine, illustrated in Fig. 170, has been found
satisfactory for petroleum oils as heavy as 30° Baum6 (see Table
7, Chapter XII). This engine is provided with an un jacketed
vaporizer A, which communicates with the cylinder by means of

INTERNAL COMBUSTION ENGINES

205

the small opening B. The vaporizer is raised to a red heat before
starting, by means of a torch, and is kept hot by repeated explo-
sions when the engine is running. This engine works on the
regular four-stroke Otto gas-engine cycle. During the suction
stroke of the piston only air is sucked into the cylinder and the
charge of oil fuel is injected into the vaporizer by a pump. On
the return stroke the air is compressed, forced into the vaporizer,
mixed with the fuel and automatically ignited. This is followed
by the expansion and exhaust strokes, as in other internal com-
bustion engines.
A modification of this type of engine is the so-called semi-

Fig. 171. — Semi-Diesel oil engine.

Diesel type of oil engine, which can be operated on the lowest
grades of petroleum fuels. One type of semi-Diesel engine
is illustrated in Fig. 171. Like the Diesel, the semi-Diesel engine
compresses only air, but operates at a compression pressure of
about 300 pounds per square inch, depending partly on a hot
unjacketed combustion chamber to ignite the charge. During
the suction stroke a charge of air is drawn into the cylinder,
which is compressed into the combustion space. At or near the
end of the compression stroke, the fuel oil is admitted in a fine
spray, is mixed with the air and is ignited. The resulting expan-
sion forces the piston on its working stroke. Near the end of the
working stroke, the exhaust valve is opened and the piston on its

206 STEAM AND GAS POWER ENGINEERING

return stroke expels the burnt charge. An indicator card from
a semi-Diesel oil engine is illustrated in Fig. 172.

The Diesel engine, previously described, is the most economical
type of engine for low grades of fuel. While its high cost limits
its field of application in small sizes, this is compensated in sizes
of 100 horsepower and greater by the higher fuel economy and
by the ability of this type to operate on any liquid fuel without
leaving an appreciable residue. Recent tests indicate that Diesel
engines will consume only about 0.45 pound of low grade oil per
brake horsepower per hour.

Fig. 172. — Indicator card from a semi-Diesel oil engine.

Losses in Internal Combustion Engines. — Internal combus-
tion engines convert 10 to 30 per cent, of the heat energy supplied
by the fuel into useful mechanical work. The two greatest
losses are those due to the heat carried away by the jacket water
and by the exhaust gases. The loss in the jacket water will vary
from 25 to 40 per cent, of the heat supplied by the fuel. The loss
of heat in the exhaust gases, owing to their high temperature,
will vary from 25 to 50 per cent, of the heat supplied, increasing
as the jacket loss decreases.

The other main losses are those due to incomplete combustion
of the fuel, heat radiated from the outer surfaces of the engine,
and frictional losses in the mechanism of the engine.

Installation and Care of Internal Combustion Engines. — The
general rules govering the installation of steam-power plant
equipment apply to internal combustion engines. An engine
should be installed in a well-lighted and ventilated room, which
is free from dirt and dust. The engine room must be large enough
so that there is sufficient space for easy access to any part of the
engine so as to facilitate starting, oiling, inspection, and repair of
all parts.

INTERNAL COMBUSTION ENGINES 207

In installing oil engines, the fuel tank should be located outside
the building and preferably underground. In any case the tank
should be lower than the pipe to which it is connected in the
engine room.

As the mixture of fuel and air is ignited inside the engine
cylinder, the resulting explosion produces a shock of consider-
able magnitude on the engine mechanism, which in turn is trans-
mitted to the foundation. This necessitates very carefully built
foundations, which should be separated from the walls of the
building, so that vibrations caused by the engine will not affect
the building or the surrounding structures.

The exhaust piping should be as straight and as short as
possible and the exhaust gases should discharge out of doors.
The air supply is preferably taken from the outside.

Betore an engine is started for the first time, all the work-
ing parts should be carefully examined and placed in proper
condition.

The gas engine is not self -starting, as is the steam engine when
steam is turned on. The reason for this is that the explosive
mixture of fuel and air must be taken into the cylinder and
compressed before it can give up energy by explosion. It is,
therefore, necessary to set the engine in motion by some external
means not employed in regular operation, before it will pick up
its normal cycle.

Small engines are started by hand. This is accomplished by
turning the fly-wheel over by hand in the direction of normal
rotation until the engine picks up, or by turning it in opposite
direction against compression and then snapping the igniter by
hand. As it is difficult to pull over an engine by hand against
compression throughout the whole cycle, some engines are pro-
vided with a starting cam, which can be shifted so as to engage
the exhaust lever. This relieves the compression while crank-
ing, as the exhaust port is open during the first part of the com-
pression stroke. After the engine speeds up the starting cam is
disengaged. Most small engines and also all engines for auto-
mobiles, tractors, and trucks are provided with starting cranks.
Starting cranks are arranged so that, when turned in the direction
of rotation of the engine, they grip the shaft. The starting crank
is released as soon as the engine shaft turns faster than the crank.

208 STEAM AND GAS POWER ENGINEERING

As the size of the engine increases hand methods for starting
cannot be used. Stationary gas and oil engines are usually
started by compressed air. If the engine consists of two or more
cylinders, this can be accomplished by shutting off the gas
supply to one of the cylinders and running this cylinder with
compressed air from a tank, in the same manner as a steam engine
is operated with steam from a boiler. As soon as the other
cylinders pick up their cycle of operations the compressed air is
shut off and a mixture of fuel and air is admitted to the cylinder
used in starting. With large gas engines of only one cylinder,
the compressed air is admitted long enough to start the engine
revolving, when the compressed air is shut off and the mixture of
fuel and air is admitted. The air supply for starting is kept in
tanks which are charged to a pressure of 50 to 150 lb. by a small
compressor, driven either from the engine shaft, or by means of
an auxiliary motor.

In electric central stations starting by electricity is the simplest.
Electric starting systems are also used generally on modern
automobiles as will be explained in Chapter XVI.

Before an internal combustion engine is started, the fuel
supply should be examined, the ignition system tested, the lubri-
cating devices examined and placed in proper working condition,
the load disconnected from the engine, and the spark mechanism
retarded to the starting position. In starting an engine by hand
cranking, the operator should always pull up on the crank. As
soon as the engine starts, the spark should be advanced to the
running position and the engine connected to its load.

To stop an engine, the fuel valve is closed, the switch control-
ling the ignition system is opened, the lubricators and oil cups
are closed, and the jacket water is turned off. In cold weather
the water from the engine jackets should be drained to prevent
freezing. Before leaving the engine it should be cleaned, all
parts examined and put in order ready for starting up.

The operation and the economy of an internal combustion
engine is greatly influenced by the proper timing of the valves
and of the point of ignition. The exact setting of the valves and
of the point of ignition depends upon the speed of the engine and
upon the fuel used.

The exhaust valves should open before the end of the power

INTERNAL COMBUSTION ENGINES 209

stroke and generally from 25° to 40° before the crank reaches the
outer or crank-end dead center. This is necessary to prevent loss
of power when the piston starts on the exhaust stroke. The time
of opening of the exhaust valve must be earlier for high-speed
than for slow-speed engines. The exhaust valve should remain
open until the crank has turned 5° to 12° beyond the completion
of the exhaust stroke. The suction stroke follows the exhaust
stroke, and, in order to prevent the mixing of the fresh charge
with the burnt gases, the inlet valve should open about 3° after
the exhaust valve closes. The time of closing of the inlet valve
should be after the crank has turned 10° to 25° beyond the comple-
tion of the suction stroke. To ascertain if the valves of an
engine are properly timed, the fly-wheel should be turned over
slowly and the time of opening and closing of each valve noted.
The proper setting of the valves can be accomplished by changing
the length of the valve push rods or by changing the timing
of the valve gear shaft. If for any reason the gears are removed
on the crank shaft or on the valve gear shaft, care should be
taken that they are properly replaced, as one tooth out of place
will throw the valve mechanism out of time.

The exact point of ignition
depends upon the system of
ignition, the speed of the en-
gine, the compression, and
upon the fuel used. Proper
ignition timing can best be de-
termined by means of an indi-
cator. Indicator cards show-
ing early, late, and proper igni- FlG- ^.--Indicator cards showing early,
. . 7 x r- o latet ancj proper ignition.

tion are illustrated in Fig. 173.

If an engine runs well at no-load but will not carry its rated
load, the fault may be due to: poor compression, poor fuel,
defective ignition, poor timing of ignition, incorrect valve setting,
incorrect mixture, leaky inlet or exhaust valves, too much fric-
tion at bearings, or to the engine being too small for the rated load.

Premature ignition, usually called preignition, is due to the
deposition of carbon or soot on the walls of the cylinder, the com-
pression being too high for the fuel used; by over-heating of the
piston, exhaust valve, or of some poorly jacketed part.

210 STEAM AND GAS POWER ENGINEERING

Best results will be secured if the operation of an engine is
placed in charge of one man who is held responsible for the con-
dition of the motor.

Problems

1. Can an economical internal combustion engine be developed to oper-
ate upon a one-stroke cycle? Give reasons for your answer.

2. How does the combustion of the mixture in an Otto cycle engine com-
pare with the explosion of gunpowder?

3. Under what conditions is the two-stroke cycle engine most practical?

4. Why are higher compression pressures more practical with blast fur-
nace gas than with natural gas.

5. At what temperature should the water in the jacket of a gas engine be
maintained? Give reasons for the temperature used.

6. Compare poppet and slide valves for internal combustion engines.

7. Why will an automatically operated inlet valve decrease the power of a
gas engine?

8. An oil engine is found to deliver 150 horsepower when tested at sea
level. Will this engine develop the same power at Denver, Colorado?
Give reasons for your answer.

9. Explain the difference between preignition and backfiring.

10. Check and correct the valve setting of some internal combustion
engine.

11. Failure of an internal combustion engine to start is due to what
causes? Explain in detail causes and remedies.

12. If an internal combustion engine slows down and stops, apparently
without cause, where would you look for trouble? Explain in detail.

13. Black smoke issues from the exhaust of a gas engine. What is this an
indication of? What causes blue smoke at the exhaust?

14. What will cause the deposition of carbon on the cylinder walls?

CHAPTER XII
INTERNAL COMBUSTION ENGINE FUELS AND GAS PRODUCERS

Fuels

Classification of Fuels. — -Solid, liquid, and gaseous fuels are
used in internal combustion engines. The value of a fuel de-
pends upon its heating value, upon its cost, upon the rapidity
with which it burns, and upon the cost of preparing it for use in
the gas engine cylinder. The fuel must be capable of being
transformed into a vapor or a gas before entering the engine
cylinder, must readily combine with air to form an explosive
mixture, and should leave no residue or ash after combustion.

Gaseous fuels are the simplest for use in internal combustion
engines. The fuel in the gaseous state requires simply a mixing
valve to proportion the air and the fuel before the mixture enters
the engine cylinder. For this reason when a suitable gaseous
fuel can be obtained at a low cost it is generally preferred.

Solid fuels in their natural state cannot be used for internal
combustion engines. The chief difficulty experienced in their
use is from the ash or residue which remains after combustion.
Several attempts have been made to inject coal dust directly into
the cylinder of an internal combustion engine, but the resulting
ash seriously interferes with the operation. Gunpowder as a fuel
has also been attempted, but has not proved successful. The
only successful method of utilizing the energy of solid fuels at the
present time is to transform the fuel from the solid to the gaseous
state. The gas producer, to be explained later, is one of the most
practical means by which this transformation is accomplished.
The use of solid fuel requires considerable extra equipment, but
has proved practical in many instances.

Liquid fuels are comparatively inexpensive in certain localities,
are easily transported, and large quantities of such fuels may be
stored in a comparatively small space. Petroleum distillates
are used most commonly in internal combustion engines al-

211

212

STEAM AND GAS POWER ENGINEERING

though alcohol, tar, tar oil, shale oil, and phenoloid (liquid fuel
from blast furnaces) are also employed to some extent.

The Heating Value of a Fuel. — The heat content of a liquid
or gaseous fuel is an important index of its value, as is the case
of solid fuels discussed in Chapter II. This property is measured
in much the same manner as is the heating value of coal. The

Fig. 174. — Gas Calorimeter.

fuel is burned in some form of calorimeter and the heat liberated
is measured by the amount of heat absorbed by the water which
surrounds the combustion vessel or chamber of the calorimeter.
In Fig. 174 is illustrated a calorimeter for determining the heating
value of gaseous fuels. This type of calorimeter with special
equipment is also used for testing light liquid fuels.

The apparatus (Fig. 174) is designed for determining the num-

FUELS AND GAS PRODUCERS 213

ber of heat units in a certain volume of gas, as a cubic foot or a
cubic meter.

The gas enters the meter at g and passes thence through the
pressure regulator to the calorimeter proper, where the gas
burns at the burner shown in dotted outline.

The products of combustion rise to the top where they enter
and pass down through a double row of pipes which are surrounded
by circulating water and leave at the exit flue at the base.

The water entering at a, passes through the regulating cock e,
thence around the tubes and issues at c, whence it flows into the
measuring glass.

Thermometers register the temperatures of the gases and the
water entering and leaving the calorimeter.

Knowing the volume of gas burned, the quantity of water
collected, and the temperatures above noted, a simple calcula-
tion gives the heating value of the gas.

Selection of a Fuel. — -While the heating value of a fuel is an
important index of its value several other properties are usually
considered.

The value of a solid fuel depends upon the percentage of water
it contains, the amount of ash, the tar-forming ingredients, and
whether it is of a coking or non-coking variety. Moisture
simply dilutes the gas generated and consequently lowers its
heating value per cubic foot. A high percentage of ash in the
fuel requires more frequent cleaning of the producer and often
causes a partial stoppage of the air supply. Coking fuels require
constant breaking up of the charge with the consequent hindrance
in the operation of the producer. The formation of tar, which
results when bituminous or high volatile coals are gasified, re-
quires cleaning of the gas before it enters the gas engine cylinder.
Tar in the cylinder leaves a large deposit of soot, which inter-
feres with the operation of the engine. Anthracite coal and coke
are perhaps the ideal solid fuels for gas producers, because of the
absence of tar, although other varieties of coal and lignite are used
to a certain extent.

The quality of a liquid fuel depends upon its specific gravity,
flash point, water content, cold test, color, sulphur content,
presence of acids, and residue.

By specific gravity is meant the relation existing between

214 STEAM AND GAS POWER ENGINEERING

the weight of any substance and the weight of an equal volume or
bulk of water. The Baume hydrometer (Fig. 175) is generally
used for this determination. This instrument carries an arbi-
trary scale and sinks to a depth corresponding to the density of
the liquid in which it floats. Table 7 shows the relation existing
between the Baume* hydrometer scale, the specific gravity, and
the weight of liquid fuels in pounds per gallon.
Formerly liquid fuels were judged mainly by their
I i l|J|r specific gravity. In the case of blended fuels,

■] | specific gravity is not an accurate indication of

its quality.

The flash point of a liquid fuel is the lowest
temperature at which the vapors arising there-
from will ignite when a small test flame is brought
near its surface. The flash point is an index of
the volatile constituents of a fuel.

The cold test is the lowest temperature at
which a liquid fuel will pour. Upon this prop-
erty depends the free circulation of liquid fuels
through pipes.

Gaseous fuels to be suitable for internal com-
bustion engines must be free from dust, tar, sul-
phur vapors, and other impurities.

Distillates of Crude Petroleum. — The so-called
distillates of crude petroleum are obtained by
boiling or refining crude petroleum, and condensing the vapors
which are driven off at various temperatures. Crude petroleum
is a mineral oil which is found in greatest quantities in the
United States, Russia, Mexico, and Rumania. The exact com-
position of crude petroleum varies in different localities. It is
made up mainly of carbon and of hydrogen, in the ratio of about
two-thirds carbon to one-third hydrogen. Crude petroleum in
certain localities has a paraffin base; that is, it yields a solid
paraffin residue. Other petroleums with an asphalt base yield
an asphalt residue. The specific gravity of petroleum oils from
different fields varies between 0.800 and 0.970.

The vapors which are condensed into gasoline are driven off
at temperatures of 140 to 160°F. The various grades of kero-
sene are the condensed vapors, driven off at temperatures of

Fig. 175. — Baume
hydrometer.

FUELS AND GAS PRODUCERS 215

Table 7. — Specific Gravity and Baum^ Scale

Specific

Degrees

Pounds per

Specific

Degrees

Pounds per

gravity

JJaume

gallon

gravity

Baum6

gallon

1.000

8.336

0.775

6.462

0.993

8.277

0.771

6.428

0.986

8.220

0.767

6.394

0.979

8.161

0.763

6.358

0.972

8.104

0.759

6.324

0.966

8.051

0.755

6.290

0.959

7.997

0.751

6.258

0.953

7.944

0.747

6.212

0.947

7.891

0.743

6.195

0.940

7.837

0.739

6.163

0.934

7.785

0.736

6.133

0.928

7.736

0.732

6.101

0.922

7.687

0.728

6.070

0.916

7.638

0.724

6.038

0.911

7.590

0.721

6.006

0.905

7.541

0.717

5.975

0.899

7.493

0.713

5.946

0.893

7.444

0.710

5.916

0.887

7.395

0.706

5.886

0.881

7.347

0.703

5.856

0.876

7.298

0.699

5.827

0.870

7.254

0.696

5.797

0.865

7.210

0.692

5.771

0.860

7.166

0.689

5.743

0.854

7.122

0.686

5.715

0.849

7.079

0.682

5.688

0.844

7.038

0.679

5.659

0.840

6.998

0.676

5.632

0.835

6.696

0.672

5.603

0.830

6.918

0.669

5.576

0.825

6.878

0.666

5.548

0.820

6.839

0.662

5.517

0.816

6.804

0.658

5.487

0.811

6.760

0.655

5.457

0.806

6.721

0.651

5.427

0.802

6.683

0.648

5.402

0.797

6.644

0.645

5.374

0.793

6.608

0.642

5.353

0.788

6.571

0.639

5.316

0.784

6.534

0.636

5.304

0.779

6.498

216 STEAM AND GAS POWER ENGINEERING

250 to 400°, and the heavy oils are driven off at still higher
temperatures.

Gasoline. — Of all petroleum distillates, gasoline is the most
important fuel for automobiles, airplanes, and small stationary
and portable internal combustion engines. The consumption of
gasoline has increased in the United States more than 700 pec
cent, during the past ten years. The yield of gasoline, however,
is very small in comparison with the heavier distillates. By re-
fining American petroleum, an average of less than 5 per cent, of
gasoline is obtained and usually about 50 per cent, of kerosene.
This makes gasoline more expensive than other petroleum fuels.

Gasolines may be classified as: (1) straight refinery, (2)
cracked, (3) casing head.

The straight refinery method of manufacturing gasoline from
crude petroleum is to heat the crude oil in a closed retort, called a
still, then cooling and condensing the vapors given off. Destruc-
tive distillation, or cracking, is prevented by keeping down the
temperature within the still either by placing the still under a
partial vacuum or by allowing steam to bubble through the crude
oil when distilling.

Cracked gasolines are obtained by subjecting petroleum oils
of high boiling point to high temperatures and pressure; the
heavy oil decomposes and cracked gasoline is recovered from
the distillate.

Natural gas gasoline is obtained from natural gas either by the
compression or the absorption methods. The compression pro-
cess is usually applied to wet gas, called casing head gas; that is,
to gas which is produced from the same sands as petroleum oil.
The absorption process can be used with ordinary natural gas.
A gasoline similar to casing head gasoline is also being manu-
factured in refineries by the compression process from the very
light vapors which are driven off when the stills are first heated.

Commercial gasoline is usually a physical blend of these
various grades. Its density varies from 57 to 85 degrees Baume
(0.65 to 0.75 specific gravity), depending upon its composition.
The weight of gasoline varies from 5.4 to 6.2 pounds per gallon.
Its heating value is about 19,000 B.t.u. per pound. The flash
point ol gasoline varies from 10 to 20°F. This means that gases
are liberated which form an inflammable vapor at low tempera-

FUELS AND GAS PRODUCERS 217

tures provided a sufficient supply of air is present. For this
reason care must be taken in the handling of gasoline. A good
storage tank free from leaks and placed underground contributes
greatly to the safety as well as to the economical use of gasoline.
When filling a gasoline storage tank or in handling gasoline, care
must be taken not to have any unprotected flame nearby. In
case of fire it is best to extinguish the flame by means of wet
sawdust or a special fire extinguisher.

Kerosene. — Kerosene, which can be secured in greater quan-
tities than gasoline and which has a rather limited market, ranks
next to gasoline among the products of crude petroleum for use
in oil engines. Its density varies from 41 to 49 degrees Baume
(0.78 to 0.82 specific gravity). Its flash point is 70 to 150 de-
grees depending upon the grade, and its heating value per pound
is about 18,500 B.t.u. Kerosene is less volatile than gasoline,
is safer to handle and store, does not evaporate so rapidly, but
requires preheating to produce rapid evaporation. Kerosene
is quite satisfactory as a fuel for engines operating under con-
stant loads and speeds. Any gasoline engine can be operated
with kerosene fuel provided it is started and run with gasoline
until the cylinder walls become hot. Hot bulb engines will start
on kerosene.

Crude Oil. — Distillate and fuel oils are the heavier petroleum
products which are used as fuels in Diesel or semi-Diesel types of
internal combustion engines. These fuels have a high flash
point and a heating value of 18,000 to 20,000 B.t.u. per pound.
The qualities of these oils are based principally upon their heat-
ing value and to a certain extent upon their specific gravity.

Alcohol. — Alcohol as a fuel for gas-engine use has many ad-
vantages as compared with the petroleum distillates. It is
less dangerous than gasoline, its products of combustion are
odorless, and it lends itself to greater compression pressures
than do the various petroleum fuels. Experiments show that
an engine designed to stand the compression pressures before
ignition most suitable for alcohol will develop about 30 per
cent, more power than a gasoline engine of the same size, stroke,
and speed.

Several years ago, when the internal revenue tax was removed
from alcohol, so denatured as to destroy its character as a

218 STEAM AND GAS POWER ENGINEERING

beverage, it was expected that denatured alcohol would become
a very important fuel for use in gas engines. Its price up to this
date, however, has been so much higher than that of gasoline, the
most expensive of petroleum fuels, that the use of alcohol in gas
engines is out of the question. It is possible that, as the cost of
the petroleum distillates increases, and processes are developed
for producing denatured alcohol at a low price, the alcohol
engine will come into prominence as a motor.

American denatured alcohol consists of 100 volumes of ethyl
(grain) alcohol, mixed with ten volumes of methyl (wood) alcohol,
and with one-half a volume of benzol.

The specific gravity of denatured alcohol is about 0.795 and
its calorific value is about two-thirds that of petroleum fuels.
Alcohol requires less air for combustion than do petroleum fuels.
Theoretically, the calorific value of a cubic foot of explosive
mixtures of alcohol and of gasoline is about the same. Actual
tests show that the fuel economy per horsepower is about the
same for both fuels provided the compression pressures before
ignition are best suited for the particular fuel used. In gasoline
engines compression pressures of about 75 lb. are used, while the
alcohol engine gives best results, as far as economy and capacity
are concerned, when the compression pressure before ignition is
about 180 lb. per square inch.

Benzol. — -Benzol is a liquid fuel derived from the distillation
of coal. In the pure state it has a density of about 29 degrees
Baume (0.88 specific gravity) and a heating value of about 17,200
B.t.u. per pound. When mixed with various proportions of
gasoline or of alcohol a desirable fuel results. A fifty per cent,
mixture of benzol and alcohol has been successfully used as a
fuel. Commercial benzol contains about 90 per cent, benzol
while the remaining constituents are other minor coal tar
derivatives.

Shale Oil. — Shale oil is obtained from the destructive dis-
tillation of shale in vertical retorts in which the shale is exposed
to a temperature of about 900°F. The crude shale oil has
a specific gravity of 0.86 to 0.89 and yields, by refining, oils which
are suitable for use in internal combustion engines of special design.

Fuel Gases. — The fuel gases suitable for internal combustion
engines are blast-funace gas, coke-oven gas, natural gas, and

FUELS AND GAS PRODUCERS 219

producer gas. Internal combustion engines can also be operated
on illuminating gas, acetylene, and oil gas; but these fuel gases
are usually too expensive.

Illuminating gas is manufactured by distillation of bituminous
coal and has a heating value of about 600 B.t.u. per cubic foot.

Acetylene gas is formed when calcium carbide is decomposed
by water and has a heating value of about 1,500 B.t.u. per cubic
foot.

Oil gas is produced by vaporizing crude petroleum.

Blast-furnace Gas. — 'Blast-furnace gas is made by the com-
bustion of coke during the production of pig iron. The gas,
after leaving the top of blast furnaces, can be purified and used
for operating internal combustion engines. Blast furnace-gas has
a heating value of only about 100 B.t.u. per cubic foot, but can be
compressed to high pressures with the resulting high efficiency
if used in internal combustion engines operating on the Otto
cycle. From 120,000 to 180,000 cubic feet of blast-furnace gas
are generated at the production of each ton of pig-iron, and this
is available for the generation of power as well as for the various
heating processes required in the plant. Blast-furnace gas must
be thoroughly cleaned of all fine dust and of metallic vapors
before it is used in gas engines.

Coke-oven Gas. — Coke-oven gas has a heating value of about
600 B.t.u. per cubic foot and when free from tar is suitable as a
fuel for internal combustion engines. Modern coke-oven plants
yield considerable gas for power purposes, as only about 60 per
cent, of the gas generated in the coke ovens is used as fuel for
the coking process.

Natural Gas. — Natural gas is found near practically all oil
fields and has been very successful as a gas engine fuel. The
heating value of natural gas varies ordinarily from 900 to 1000
B.t.u. per cubic foot. On account of the high hydrogen content
of natural gas, engines utilizing this fuel must operate at low
compression pressures in order to prevent preignition. Owing
to the need of natural gas as a fuel for industrial and household
use and to the uncertainty of a continued supply, its utilization
for the generation of power is limited to very few localities.

Producer Gas. — Producer gas is manufactured from solid
fuel in a brick lined vessel, called a gas producer. The gas

220 STEAM AND GAS POWER ENGINEERING

producer is blown continously with a mixture of air and steam,
in definite proportions, generating a combustible gas, which is
suitable for use in internal combustion engines or for heating.
Producer gas can be manufactured from charcoal, coke, anthra-
cite coal, bituminous coal, lignite, peat, or wood. Producers
operating on anthracite coal or coke have been more satisfactory
than those using bituminous coal or lignite, as anthracite coal
producer gas contains very little tar and the plant does not have
to be provided with elaborate scrubbing systems for cleaning
the gas.

The amount of gas generated per pound of fuel depends upon
the fuel used. Producers using lignite will usually generate less
than 40 cubic feet of gas per pound of fuel. With bituminous
coal, the gas generated per pound of fuel will be about 65 cubic
feet, with anthracite about 75, and with coke near 90 cubic feet
of gas will be produced.

Anthracite producer gas has an average heating value of
about 130 B.t.u. per cubic foot and contains approximately:
9 per cent, of hydrogen, 24 per cent, of carbon monoxide, 5 per
cent, of carbon dioxide, 2 per cent, of hydrocarbons, and about
60 per cent, of nitrogen. Bituminous producer gas has a heat of
combustion of about 140 B.t.u. and contains approximately:
12 per cent, of hydrogen, 20 per cent, of carbon monoxide, 8 per
cent, of carbon dioxide, 3 per cent, of hydrocarbons, and about
57 per cent, of nitrogen.

Internal combustion engines using producer gas can be. oper-
ated at a compression pressure before ignition of about 160
pounds per square inch and will produce a horsepower for about
75 cubic feet of gas, which can be generated in a producer by the
gasification of about one pound of coal.

Gas Producers

Details of Gas Producers. — -A gas producer is a brick-lined

air-tight steel plate cylinder arranged with a grate to hold a thick

j bed of fuel, a hopper and an ash pit to receive the fuel and the

I non-combustible material respectively, means for supplying a

mixture of air and steam to the fuel bed, a gas outlet, and gas

cleaning apparatus. Producers are usually provided with poke

FUELS AND GAS PRODUCERS

221

holes and shaking grates for breaking up and for maintaining the
fuel bed in uniform condition.

Details of a typical producer generator are illustrated in Fig.
176. Fuel is charged into the retort C and is admitted to the
shell of the generator by means of a quick-opening gate valve.
The retort C is provided with a water-sealed cover, this arrange-
ment enabling the operator to charge the producer while the
plant is in operation, without the danger of admitting air or of

Water Seal

Ooib Outlet

> Green Fuel ° -

e » Distillation Zone •
'. 700°tol300°F »>

„ Dec omposi tion Zone ,
% About ldOO°F p o

lAsh Door

Fig. 176. — Gas producer generator.

allowing gas to escape. Coal entering the shell is distributed by
means of the hood J', the inside of which serves as a gas collector.
The gas outlet is at J. A swinging grate Z supports the fuel bed
and is suspended from the shell by chains. The shaking motion
of the grate is produced by the hand lever L. Doors are provided
at the bottom for the removal of ashes. The generator is provided
with peep holes and poke holes for observing and maintaining
the fuel bed in the proper condition. The mixture of steam and
air enters at A. The temperatures of the various zones are
approximately as indicated in Fig. 176.

222 STEAM AND GAS POWER ENGINEERING

Classification of Gas Producers. — Producers are classified by
the manner in which the mixture of air and steam is caused to
pass through the producer and gas cleaning apparatus.

In the suction types of producers the air is drawn through the
producer and gas-cleaning apparatus by the suction formed in the
engine cylinder. The rate of gas formation in this type is
automatically controlled by the demand of the engine. This type
of gas producer is inexpensive and is suitable only for small
installations.

In the pressure types of producers the mixture of air and steam
is forced through the fuel bed of the producer by means of a fan.
The amount of gas generated in this case is independent of the
amount used by the engine.

In a third type, called combination producer, a fan is placed
between the producer and the engine which delivers the gas to the
engine or to a gas holder under pressure. The producer proper
in this case operates as a suction producer, but the amount of gas
generated is independent of the engine's demand.

Gas producers are also classified with reference to the fuel
gasified. Anthracite producers are usually of the suction type,
the draft being produced by the suction of the engine piston.
Bituminous producers are of the pressure or of the combination
types and are provided with special scrubbers and purifiers for
removing tar and other impurities.

Suction Gas Producers. — -A simple suction gas producer suit-
able for anthracite coal is illustrated in Fig. 177. The generator
A of the producer is a cast iron or steel shell with a grate below
and a fuel hopper above. Steam for the blast is generated in a
vaporizer, which is either arranged around the top of the pro-
ducer or is independent of, but attached to, the producer proper.
The mixture of air and steam enters at the bottom of the fuel
bed, a valve regulating the proportion of air and steam. The gas
leaving the producer is cooled and purified in a coke-filled wet
scrubber S and passes to the engine cylinder C.

In some suction producer plants the gas is cooled and cleaned
of dust in a water-sprayed coke scrubber, after which it is allowed
to pass through a dry scrubber on its way to the engine. The
dry scrubber is filled with shavings, excelsior, and iron turnings
and is intended to remove sulphurous fumes from the gas.

FUELS AND GAS PRODUCERS

223

The hand-operated fan B (Fig. 177) is used to furnish draft
during the starting of the fires. When the engine is in operation
the draft from the fan B is not necessary. A producer is also
provided with a change valve, which is used to discharge the poor
gases to the atmosphere when the fire is started up.

Fig. 177. — Suction producer plant.

Pressure Gas Producers. — One type of pressure producer,
called the water-bottom producer, is illustrated in Fig. 178. The
grate in this case is dispensed with and the ashes drop into a
water seal at the base of the producer. The blast is admitted to
the center of the producer by a steam jet blower B. The fuel is
discharged from the hopper D into the chamber E, from which it
is distributed uniformly by the device F. Poke holes are pro-
vided at G and at H for breaking up the fuel bed. The gas
leaving the producer at C enters scrubbers, tar extractors, and
other purifiers on its way to the engine cylinder. The water-
bottom type of producer is advantageous in that the ashes can
be removed conveniently while the producer is in operation.
Some water-bottom pressure producers are provided with an
automatic fuel-feeding device.

Combination Producers. — Combination producer plants have
a blower placed between the producer and the engine cylinder.
Some plants of this type are similar to the producers described

224 STEAM AND GAS POWER ENGINEERING

and are equipped with elaborate scrubbers and purifiers when
operated with low grade fuels.

In the down-draft double furnace producer, illustrated in Fig.
179, the formation of tar is prevented by carrying the gases,
which are distilled from the fresh fuel in the upper strata,
through the hottest zone at the lower part of the producer.

Fig. 178. — Pressure gas producer.

The cleaning apparatus used with this type of plant consists only
of a wet and dry scrubber.

In starting the down-draft double furnace producer the fires
are kindled with coke and wood in both generators and the blower
is started, leaving open the top doors H and /, and valves A, B,
G, and C. Valve D is closed. As soon as the fires are thoroughly
kindled, steam is admitted to the top of the generators at F and

FUELS AND GAS PRODUCERS

225

226 STEAM AND GAS POWER ENGINEERING

E, and mingles with the air admitted through top doors H and I,
which the operation of the blower draws down through the fresh
charge of coal and then through the hot fuel bed beneath. The
gas produced is then drawn down through the grates and ash
pits of both generators, up through the vertical boiler, through
the valve G, through the wet scrubber, and blower. When valve
C is closed and valve D is opened the gas is pushed by the blower
through the dry scrubber and to the gas holder. The gas from
the gas holder is delivered to the engine cylinder.

Rating of Gas Producers. — The capacity of a gas producer is
expressed by the number of pounds of fuel it can gasify per hour
or in horsepower if the gas is generated for power purposes. The
gasifying capacity of a producer depends upon its design and
upon the quality of the fuel used. The rating in horsepower is
incorrect because no mechanical work is done by the producer
and there is no definite relation between the capacity of a pro-
ducer and the power developed by an internal combustion engine.
There is at present no standard method for rating gas producers.

Factors Influencing Producer Operation. — One of the most im-
portant factors to be considered in the selection of a gas-producer
fuel is its volatile constituents. The fuel that produces tar and
lampblack in large quantities will require complicated scrubbing
systems, or producers of special design. This will in either case
increase the first cost of the plant as well as the cost of the upkeep
of engines and pipe lines. The amount of tar-forming gases is
small with anthracite coal, but is considerable in the case of most
bituminous coals and lower grades of solid fuels.

The kind of ash is also of importance. If the ash fuses or fluxes
to a clinker, the proportion of steam to air in the blast must be
increased to reduce the temperature of the fuel bed. This de-
crease in temperature reduces the percentage of combustible car-
bon monoxide formed in the producer. The use of too much
steam in the producer results in the formation of a gas which has
considerable hydrogen. This means that when used in internal
combustion engines the gas cannot be compressed to as high a
pressure as producer gas which has little hydrogen.

Clinker formation is also serious because it obstructs the gas
passages, requiring increased blast pressure to allow the air to
pass through the fuel bed. Uniform conditions during producer

FUELS AND GAS PRODUCERS 227

operation and careful poking will reduce the difficulties from
clinker.

The size of coal used influences the capacity and efficiency of a
gas producer. If the coal is too large, too little surface is offered
for gasification and the producer efficiency is reduced. A nut-
size of bituminous coal is best while the pea-size anthracite will
give good results. If the coal is too fine, the resistance through
the fuel bed is increased, requiring greater blast pressure, and
this reduces the capacity of the producer.

The grate area, the rate of gasification, and the depth of the
fuel bed are affected by the character of the fuel, the lower grade
fuels requiring a larger grate area, slower rates of gasification, and
deeper fuel beds.

Some form of gas calorimeter will prove very useful in the daily
operation of gas producers.

Problems

1. An analysis of a gas by the gas calorimeter (Fig. 174) gave the follow-
ing readings: Gas passed through meter 3 cubic feet, water collected 85
pounds, inlet temperature 65°F., outlet temperature 84°F. Calculate the
heating value of the gas in B.t.u. per cubic foot.

2. Compare the relative values of gasoline, kerosene, alcohol, and crude
petroleum for use in internal combustion engines.

3. At what price must the ordinary illuminating gas sell in order to com-
pete with natural gas at 50 cents per thousand cubic feet?

4. Under what conditions is the gas-producer plant most suitable for
power generation?

CHAPTER XIII
AUXILIARIES FOR INTERNAL COMBUSTION ENGINES

Carburetors

Principles of Carburetion.— To successfully operate an internal
combustion engine on liquid fuel it is necessary to vaporize the
fuel and mix it with air in the correct proportions for use in the
engine cylinder. This process of vaporizing and mixing the fuel
with air is known as carburetion. The function of a carburetor
is automatically to vaporize the liquid fuel, and mix it with air
in the correct proportions by weight for use in the engine cylinder
and at all speeds of the engine.

A mixture too rich, that is, having too large a proportion of
gasoline to air, will give off a black, odorous exhaust due to the
fact that some of the gases are unburned. A mixture too lean,
that is, having insufficient gasoline, is slow burning and, conse-
quently, may result in back-firing through the carburetor. A
lean mixture is accompanied also by the heating of the motor and
by a loss of power.

Carburetors. — -Practically all modern carburetors use some
form of spray nozzle for vaporizing the fuel. A throat, or Ven-
turi tube, is usually made use of to increase the velocity of the
air at the spray nozzle, thereby increasing the spray of gasoline
from the nozzle.

Simple Carburetors or Mixer Valves. — -The simpler forms of
carburetors which are used on stationary and constant speed
engines are called mixer valves. Mixer valves are not suitable
for variable speed motors.

Fig. 180 represents the constant level, or overflow cup, type
of mixer valve. B represents the reservoir in which the constant
level of fuel is kept. A is the supply pipe. Gasoline is forced
by means of a pump, operated by the engine, through the pipe A.
0 is the overflow pipe the top of which is located just below the

228

INTERNAL COMBUSTION ENGINES

229

Fig. ISO. — Mixer valve.

top of the nozzle Ar. Air enters at C, and on the suction stroke
of the engine rushes past the nozzle N, picking up and mixing
with the spray of gasoline which is regulated by the needle valve
V. The valve V is the only adjustment on this mixer valve.

Float-feed Carburetors. — -At present,
some form of the float-feed type of carbu-
retor is exclusively used on automobiles,
trucks, and other variable speed motors.
Float-feed carburetors are of two types :
first, the concentric, in which the float
chamber surrounds the mixing chamber,
or is concentric with it; second, the
eccentric, which has the float chamber
and mixing chamber side by side. The
concentric type keeps the fuel at the pre-
determined level much better than the
eccentric carburetor. In the concentric
type, the height of the fuel in the nozzle

is not changed by road inclinations, whereas in the case of the
eccentric type the fuel level may become very low or may be
high enough to actually flow from the nozzle. Many of the
successful modern carburetors are of eccentric type, because
other advantages or conveniences more than offset the disad-
vantages mentioned above.

The Kingston Carburetor. — -Fig. 181 represents a concentric
float-feed type of carburetor. Gasoline enters at G, flowing
past the valve V into the float chamber W. The valve V is
connected to the float F by means of a lever pivoted near its
center. When the gasoline reaches the correct level, the float
is so set that it closes the valve V by means of the lever men-
tioned. The correct level of gasoline varies in different carbure-
tors somewhere between J^2 and He inch below the top of the
spray nozzle. Air enters the carburetor at A, passes downward
to the base of the carburetor, thence upward past the spray nozzle
J, where it is mixed with the gasoline. The mixing chamber
around J has a reduced area, called the throat or Venturi tube.
This is arranged to increase the velocity of the air at this point,
thereby producing more suction on the gasoline supply. S is the
gasoline adjusting screw which regulates the supply of gasoline

230 STEAM AND GAS POWER ENGINEERING

by regulating the neeedle valve at J. Turning the screw S to
the right decreases and turning to the left increases the amount
of fuel used. The quantity of mixture used is regulated by the
throttle E.

As the speed of the engine increases, the velocity, but not
the quantity, of the air in the Venturi increases and the
suction on the gasoline becomes also greater. As a result
of this, the actual supply of gasoline increases, making the mix-
ture too rich. This is true with any simple carburetor,
and therefore some means must be provided automatically to

Fig. 181. — Kingston carburetor.

govern the supply of gasoline. Some carburetors employ
auxiliary air valves, other types have compound nozzles, while
several designs employ a combination of nozzles and Venturis.

In the Kingston carburetor (Fig. 181) the desired result is
obtained by an auxiliary air valve. This is a gravity valve
consisting of several brass balls M arranged in a semicircle.
The balls are so designed that when the suction becomes great
enough to make the mixture too rich, the force of gravity on the
balls will be overcome by this suction, and they will be lifted
off their seats thereby admitting more air into the rich mixture.
The auxiliary air does not pass the nozzle in this type of carbu-
retor. The amount the balls lift off their seats is determined
by the suction resulting from the speed of the engine.

INTERNAL COMBUSTION ENGINES 231

Marvel Carburetor. — Fig. 182 represents a sectional view of
the Marvel carburetor, which is of the multiple jet, eccentric
float-feed type. There are two spray nozzles — one for low and
one for high speeds.

The low speed nozzle with its throat is situated in the un-
obstructed air passage. The needle valve in this nozzle regulates
the amount of gasoline. Turning the needle valve to right, or
up, makes the mixture leaner and to the left, or down, makes

THROTTLE

Gaso/ine
Air

GASOLINE
ADJUSTMENT

Fig. 182. — Marvel carburetor.

the mixture richer. When the speed of the motor becomes
great enough the resulting suction overcomes the force of the air
valve spring, and the air valve opens, thereby cutting in the
high speed nozzle into the air passage.

The high speed adjustment consists of tightening or loosening
the tension on the spring, which controls the air valve. For
a richer mixture, it would be necessary to turn the air adjust-
ment screw to the right or clockwise, and vice versa for a leaner
mixture.

The Marvel carburetor is rather distinctive in having a hot-

232 STEAM AND GAS POWER ENGINEERING

air jacket surrounding the mixing chamber. Hot-air is taken
off the exhaust manifold for heating the mixing chamber, thereby
aiding in the vaporization of the fuel. By means of a butter-fly
valve the operator is able to control the admission of heat to the
hot-air jacket.

Stewart Carburetor. — Fig. 183 represents a Stewart carburetor.
It is of the eccentric type and makes use of a metering pin to

Fig. 183. — Stewart Carburetor.

measure out the proper amount of gasoline for all motor speeds.
The gasoline enters through the strainer Z into the float chamber
C and past the needle valve G. From the float chamber, by
means of the small passages, the fuel passes to the well sur-
rounding the metering pin P and into the lower end of the
aspirating tube.

At the lower engine speeds air enters the combining tube
through the drilled passages H. In the combining tube it

INTERNAL COMBUSTION ENGINES

233

is mixed with the vaporized gasoline which has passed the meter-
ing pin into the aspirating tube. The passages H are open at
all times, but the valve A is held closed by its weight until
opened by the increased suction of the motor at the higher
speeds. As A rises due to suction, the lower end of tube is
less obstructed by the metering pin on account of the taper of the
pin. This larger opening then permits of increased gasoline
supply on the higher speeds. The taper of the pin is such that

Throttle Valve,

ThrofHe
, Shaft- or Stem

Large Venturi-
Small Venturi

Mixture Control ,
Valve or Choker/

Idle Discharge Jet

Idle Adjustment Needle

Floe* t Needle

F5W22

Accelaroitinq Well-
Idling Tube--^

■ Floor

Fig. 184. — Stromberg plain-tube carburetor.

the proper amount of gasoline for all engine speeds is automat-
ically taken care of.

The only adjustment is by means of the worm N and pinion,
by which the metering pin may be lowered for increased gasoline
supply and raised for decreased supply. For starting in cold
weather, it becomes necessary to increase the gasoline supply by
adjusting the dash control. Usually the control is left part way
out until the motor has become thoroughly warmed up.

The Stromberg Carburetor. — Fig. 184 represents the Strom-
berg plain-tube carburetor. A plain-tube carburetor is one
in which both the air and the gasoline openings are fixed in

234 STEAM AND GAS POWER ENGINEERING

size. In this carburetor the proper proportion of air to gasoline
is maintained at all motor speeds by means of what the manufac-
turer calls an air bled jet. Air is taken in through the air bleeder
and discharges into the gasoline channel before the gasoline
reaches the jet holes in the Venturi. The air enters the tube at
right angles to the flow of gasoline, thereby breaking up the flow
of gasoline and producing a finely divided spray. When this
spray reaches the jet holes and is discharged into the high velocity
air stream, it is further broken up and enters as a very finely
divided mist.

COMPENSATOR

Fig. 185. — Zenith carburetor.

Fig. 186. — Holley carburetor.

An accelerating well is made use of to facilitate sudden in-
creases in the speed of the motor.

The air when the engine is idling is drawn from below the
throttle and mixes with the gasoline before reaching the idling
jet. Under certain conditions, the suction draws gasoline from
both idling jet and small Venturi, but as the throttle is opened
more, the gasoline comes only from the Venturi. The function
of the large Venturi is to aid in more finely dividing the gasoline
vapor and further to mix it in the correct proportion with air.

The plain-tube Stromberg carburetor has two adjustments,

INTERNAL COMBUSTION ENGINES

235

one for low and one for high speeds. The low-speed screw adjusts
the amount of air, and the high-speed screw regulates the quantity
of gasoline.

Zenith Carburetor. — Fig. 185 represents a Zenith carbure-
tor, which is of the eccentric float-feed type, and makes use of a
compound nozzle to control automatically the amount of gaso-
line at all speeds of the motor.

Speecf
Adjustment

Fig. 187. — Kerosene carburetor.

The Holley Carburetor. — The Holley puddling type carburetor
is illustrated in Fig. 186. The gasoline enters the float chamber
in much the same manner as in any other carburetor. From the
float chamber the gasoline passes to the needle valve. The fuel
level is above the point of the needle valve and, consequently,
the gasoline rises above the needle valve, fills the puddle cup
C, and submerges the lower end of the copper tube T. The

236 STEAM AND GAS POWER ENGINEERING

Holley carburetor has only one source of air supply, there being
no auxiliary air valve. All the air passing through the carburetor
must pass over the puddle of gasoline in cup C.

The needle valve N regulates the amount of gasoline supplied
to the well, and is the only adjustment on this carburetor.

Kerosene Carburetors. — The Kingston carburetor is used to
some extent on engines operating with kerosene. When this
is done, there are two separate and distinct carburetors connected
by a three-way valve to the intake manifold. One of the car-
buretors is adjusted for gasoline and is used in starting; the other
is adjusted for kerosene. After the engine is started and warmed
up, the three-way valve is turned and the kerosene carburetor
is connected with the intake manifold.

Another form of carburetor for burning heavy fuels is illus-
trated in Fig. 187. A connection from the exhaust pipe heats
the bowl of the carburetor. This heat is necessary in order to
vaporize the heavier fuels. Above the needle valve J is placed
a set of stationary blades resembling the rotor of a windmill.
The high velocity air stream laden with particles of un vaporized
kerosene strikes these blades and is given a whirling effect. This
throws the particles of fuel, due to their inertia, against the sides
of the heated bowl and vaporizes them so that they can be mixed
properly with the air for use in the cylinder. This carburetor
has two needle valves, two adjustments, as noted in Fig. 187,
and also an auxiliary air valve.

Ignition Systems

For igniting the fuel charge in an internal combustion engine
two methods are employed: the electric spark, which is most
commonly used, and the automatic ignition system, which is pro-
duced by the heat to which the air or the mixture of air and fuel
in the cylinder is subjected.

In some of the older makes of engines the hot tube system is
employed. The tube, open at one end and closed at the other, is
made of porcelain or of some nickel alloy. The closed end of the
tube is heated by a Bunsen burner. During the compression
stroke a portion of the mixture is forced into the tube and is
ignited by the hot walls. The walls of the tube are then kept

INTERNAL COMBUSTION ENGINES 237

hot by heat caused from the explosions. Low first cost and low
upkeep are the only points in favor of this system, but they are
more than offset by the difficulty in regulating the time of
ignition.

Electric Ignition Systems. — Two electric ignition systems are
in use, the make-and-break and the jump-spark. In the case of
the make-and-break system, the spark is similar to that pro-
duced when one electric wire connected to a battery is drawn
across another, or to the spark produced by the opening of a
switch. The spark in this system is produced by the contact and
quick separation of metallic points located within the clearance
space of the cylinder. In the jump-spark system, a current of
high voltage is used which jumps across a small air gap within
the clearance space of the cylinder.

The Make-and-break System of Ignition. — The principle of
the make-and-break system of ignition is illustrated in Fig.
188. B is the battery which supplies the electric current for
ignition. C is an inductance spark coil, often called a kick coil.
It consists of a bundle of soft iron wires, called the core, sur-
rounded by many turns of insulated c
copper wire through which the cur- i

rent passes. On account of the in- ^ [_

ductive action of such a coil, the spark //w T K_ s

is greatly intensified, producing a ( x° ) ) Ljj

strong arc from a battery of low volt-
age. S is a stationary electrode well
insulated from the engine, and M a
movable electrode not insulated from

the engine. Both electrodes are V* ^A2A2A2A2A2r-,

Set in the Combustion space of the Fig. 188.— Make-and-break

cylinder. ignition systera-

The contact points of the two electrodes are brought together
by means of the cam T operated by the valve gear shaft of the
engine. When the switch W is closed current will flow through
the circuit as soon as the contact points of the electrodes are
brought together by the cam T. A sudden breaking of the con-
tact, aided by a spring, causes a spark to pass between the points
which ignites the mixture. The more rapidly the electrodes are
separated the better is the spark produced.

238 STEAM AND GAS POWER ENGINEERING

The contact between the two electrodes of the make-and-
break system may also be made by sliding one contact point over
the other. This type is known as the wipe-spark igniter and is
illustrated in Fig. 189. B is the stationary insulated electrode

Fig. 189. — Wipe spark igniter.

and A is the movable electrode. B is made in the form of a
spring and may be moved toward the electrode A by means of a
screw. The wiping action of this igniter keeps the points clean
at all times.

Fig. 190. — Hammer-break igniter.

Fig. 190 illustrates the hammer-break igniter. M is the
movable and S the stationary insulated electrode. The points
are rapidly separated by a sort of hammer blow furnished by the

INTERNAL COMBUSTION ENGINES

239

action of the springs on the end of the movable electrode. The
hammer-break igniter is more commonly used than the wipe
spark on account of the easier adjustment and less wear of the
contact points.

The Jump Spark System of Ignition. — The principle of the
jump spark system is illustrated in Fig. 191. A is a spark plug,
the points E and F of which project into the cylinder. These
points are stationary, are insulated from each other, and are
separated by an air gap of about
J^2 inch. When the switch W is
closed, the current from the bat-
tery B flows through the timer T,
which completes the circuit at the
proper time through the induction
coil I. The induced high voltage
current produces a spark at the Q)
gap of the spark plug, igniting the
explosive mixture in the cylinder.

The induction coil 7, Fig. 191,
differs from the inductance coil
used in connection with the make-
and-break system of ignition (Fig.
188), in that there are two layers
of insulated copper wire wound around the soft wire core of the
induction coil, whereas in the inductance coil there is only one
winding, the primary. The winding immediately surrounding
the core consists of several turns of fairly large insulated copper
wire and is known as the primary winding. The outside winding
is known as the secondary and consists of a large number of turns
of very fine insulated wire. It is wound over the primary with-
out any metallic connections. In some cases a common end or
terminal is used, in which case this terminal is grounded thereby
eliminating one ground wire.

The primary current must be broken or interrupted in order
to induce a current in the secondary winding. In the common
form of induction coil this is done by means of vibrator, some-
times called an interrupter. The function of the vibrator is to
break the primary circuit with great rapidity, thereby inducing
a high voltage alternating current in the secondary winding.

Fig. 191.

-Jump-spaik ignition
system.

240 STEAM AND GAS POWER ENGINEERING

This results in a series of sparks at the air gap of the spark
plug.

An electric condenser K is made use of to prevent the burning
of the vibrator points. It consists of alternate layers of tin-foil
and some insulating material such as paraffined paper and is
connected across the vibrator points. In addition to preventing
sparking at the vibrator points, the condenser absorbs the excess
current at the primary winding and again gives it up at the proper
time to increase the intensity of the spark.

The induction coil, consisting of all the parts mentioned, is
usually placed in one box and the space between the parts is
filled with some insulating material such as wax or paraffine,
in order to protect the parts from moisture.

In some cases the primary circuit is broken by some mechanical
means, thereby eliminating the vibrator. One vibrator, known
as a master vibrator, is sometimes used to break the circuit for
several coils. In either of the last two cases mentioned, the non-
vibrator type of induction coil is used.

The current from the battery B (Fig. 191) enters
the primary circuit P through the timer T and the
vibrator R. The other end of the primary is con-
nected through a ground with the other terminal
of the battery, thereby completing this circuit. As
the current flows it magnetizes the soft iron core C.
The magnetized core immediately attracts the steel
spring of the vibrator and thereby breaks the
primary circuit. The core C being of soft wire, it
immediately loses its magnetism and the spring R
is released ready again to complete the primary cir-
cuit. This vibrating action induces a high voltage
Fig. 19 2.— current in the secondary winding S, one end of
which is connected to a ground and the other to
the center post of the spark plug. The circuit is then complete
with the exception of an air gap of approximately >^2 inch at
the spark plug points, across which the current jumps, produc-
ing a series of sparks which ignite the charge.

A spark plug, such as is illustrated in Fig. 192, is used with the
jump spark system. It consists of two well insulated metallic
points. The central point is connected to a binding post which

INTERNAL COMBUSTION ENGINES 241

receives the current from the secondary or high tension- winding
of the induction coil. The other point is about J^2 inch distant
from the first and is separated from it by an air gap. The second
point is grounded through the thread of the plug to the engine
frame. The insulating materials used in the spark plugs are
mica, porcelain, and stone. The plugs are well insulated except
at the air gap.

Comparison of the Two Systems of Electric Ignition. — -The
jump spark system is much more simple mechanically, as it has
no moving parts inside the cylinder. The make-and-break sys-
tem is more simple electrically, requires less care in wiring, does
not have to be insulated so carefully, and the spark is more cer-
tain. It is difficult to lubricate the many parts of the make-
and-break system. The make-and-break system is usually used
on stationary slow-speed engines and to some extent on tractors.
The jump spark system is better adapted for high-speed and
multiple cylinder engines than is the make-and-break, and is
used on automobiles, tractors, trucks, small stationary engines,
marine engines, and airplanes.

Source of Current for Make-and-break, and Jump-spark
Systems. — -The electric current for producing the spark in the
make-and-break system may be obtained from a primary battery
of dry or wet cells, from a storage battery, low voltage dynamo, or
from a low tension magneto. The current for the jump-spark
system may be obtained from any of the above sources or from
a high tension magneto. In the latter case, the induction coil
is a part of the magneto.

Either system requires a source with about six volts pressure.
In case of a battery this may be obtained by connecting in
series 4 to 8 dry cells, or 3 to 4 storage battery cells.

Electric Batteries. — Batteries are of two types — one type,
called the primary battery, generates electrical current by means
of direct chemical action between certain substances ; another type,
called a secondary battery, or storage battery, requires charging
with electricity from some outside electrical source before it will
generate electrical energy. The active materials in the primary
battery when once exhausted cannot be brought back to generate
electricity and must be renewed, while in the storage battery the
active materials can be used over and over again.

242 STEAM AND GAS POWER ENGINEERING

The term battery is applied to two or more cells, whether
primary or storage types, when they are connected together
to increase the total amount of electrical energy delivered to a
circuit.

Primary Batteries. — A primary cell (Fig. 1 93) consists essen-
tially of a vessel containing some acid called the electrolyte, in
which are immersed two solid conductors of electricity, called
electrodes, one of which is more easily attacked by the acid than
x the other. A simple cell consists of a weak

solution of sulphuric acid, as an electrolyte,
a plate of zinc, which is easily decomposed
by the sulphuric acid, and a plate of some
other solid like copper or carbon which
resists the action of sulphuric acid. If
the plates of zinc and of copper are put
side by side in a vessel containing sulphuric
acid, and the circuit is completed by join-
ing the two plates with a wire, chemical
action will be set up within the vessel or
cell, and a current of electricity will be
^*-— * — generated.

Fig. 193.-Wet primary The dry ^ which fa uged extengively

at the present time on account of its
portability, is a modification of the cell illustrated in Fig.
193. It has zinc for the negative electrode, carbon for the
positive electrode, salamoniac and zinc chloride as the elec-
trolyte for decomposing the zinc, and some oxidizing agent like
manganese dioxide to eliminate polarization. The solution in
the dry cell evaporates slowly, so that it will become worthless
after a time, even if not used. Generally a dry cell in good con-
dition will have a current strength of 15 to 25 amperes and should
show a pressure of 134 to 1J^ volts. A binding post is attached
to the carbon and another one to the edge of the zinc cylinder.

Storage Batteries. — A storage battery consists of two sets of
plates or electrodes known respectively as positive and negative,
submerged in a liquid called the electrolyte. The plates are
encased in a jar or container. This type of battery must be
charged frequently with electricity, in order that it may con-
tinue to give out current to the external circuit. The storage

INTERNAL COMBUSTION ENGINES 243

battery does not store electricity. It stores energy in the form
of chemical work. The electrical current produces chemical
changes in the battery and these allow a current to flow in the
opposite direction when the circuit is closed.

Storage batteries are used for gas-engine ignition and are
preferred for this purpose to primary dry or wet batteries, on
account of their greater capacity and more uniform voltage.
Modern automobiles also employ storage batteries for starting,
lighting, and ignition.

The capacity of a storage battery is measured in ampere-
hours, determined by multiplying the current rate of discharge
by the number of hours of discharge of which the battery is
capable at that rate. As an illustration, a battery that will
deliver 10 amperes for 8 hours has a capacity of 80 ampere-hours.
The ampere-hour capacity of a storage battery is dependent
upon the rate of discharge. Most manufacturers specify the
rate of discharge for their particular make of storage batteries.
If the rate of discharge is greater than the specified amount,
the capacity of the battery is reduced. As an illustration, if
a storage battery has a capacity of 80 ampere-hours, at the 10
ampere rate, it will have a greater ampere-hour capacity if dis-
charged at a 5 ampere rate; that is, it will deliver a current of 5
amperes for more than 16 hours. The normal rate of discharge
is the 8 hour period.

A storage battery can be charged from any direct current cir-
cuit, provided the voltage of the charging circuit is greater than
that of the storage battery when fully charged. Before a storage
battery is connected to the charging circuit its polarity should be
carefully determined, and the positive and negative terminals of
the battery connected to the positive and negative terminals,
respectively, of the source. One good method of determining the
polarity of the wires from the storage battery or source is to im-
merse them in salt water. Bubbles of gas will form more rapidly
on the surface of the negative wire. Another test is that the
negative wire will turn blue litmus paper red. Should the posi-
tive wire of the battery be connected to the negative wire of the
source, the effect would be a discharge of the battery, and this
being assisted by the incoming current, a reversal of action would
take place. This is very injurious to the battery. It is not

244 STEAM AND GAS POWER ENGINEERING

well to charge a battery at too rapid a rate, as this will raise its
temperature and will cause buckling of the battery plates. It
is well also to charge batteries at regular intervals.

Two types of storage batteries are used — the lead storage
battery and the Edison. The Edison battery is also called the
alkaline or nickel-iron battery.

The Lead Storage Battery.— The lead storage battery, Fig. 194,
is the type used almost exclusively in connection with the modern

motor propelled vehicles. In this
battery both the positive and the
negative plates are built upon lead
grids. The perforations in the
positive grid are filled with a lead
compound (Pb02) which may be
distinguished by its brown color.
The perforations in the negative
grid are filled with spongy metallic
lead which has a dull gray color.
The positive plates are all united to
a common positive terminal and the
negative plates are all united to a
common negative terminal.

A lead storage cell, when fully
charged, will show 2.2 to 2.5 volts
on open circuit and about 2.15 volts when the circuit is
closed. A lead storage battery should not be allowed to dis-
charge to a voltage lower than 1.8 volts while giving its full rated
current. For ignition purposes, 6 and 12 volt systems are
employed.

For successful operation and long life, storage batteries should
be tested frequently with a pocket volt meter for voltage, and with,
a hydrometer for the specific gravity of the electrolyte. The
specific gravity of the electrolyte of a stationary battery
should be 1.17 to 1.22 when the battery is fully charged. A
portable battery should have a greater specific gravity,
from 1.275 to 1.300 when fully charged. Pure distilled water
must be added occasionally to the electrolyte to make up for
the evaporation. The electrolyte should be 34 to ^ inch above
the plates.

Fig. 194. — Cross-section through
lead storage battery.

INTERNAL COMBUSTION ENGINES

245

The Edison or Nickel-iron Storage Battery. — The Edison
storage battery, Fig. 195, consists of two sets of sheet-steel plates
or grids, submerged in an electrolyte of caustic potash. The
plates or grids support tubes and pockets containing the active
materials. The active materials on the plates are nickel hydrate
and a specially prepared black oxide of iron.

NEGATIVE POLE--

HARD RUBBER GLAND:

CAP

k<ELL COVER

VALVE, f'f/^R CAP G' POSITIVE POLE

f- SIDE ROD
INSULATOR

SOLID STEEL
CONTAINER

COPPERWIRE
■SWEDGED INTO
STEEL LUG

H '''CELL COVER WELDED
TO CONTAINER

'"STUFFING BOX

W-WELD TO COYER
J- GLAND RING
K- SPACING mSHER
\-- CONNECTING ROD
M- POSITIVE GRID
N- GRID SEPARATOR
0 -SEAMLESS

■ STEEL RINGS
P- POSITIVE TUBE
(NICKEL HYDRATE 8\
\NICKEL IN LAYERS )

CORRUGATIONS

SUSPENSION BOSS

CELL BOTTOM--
{WELDED TO SIDES)

Fig. 195. — Edison storage battery.

The plates are held in a steel container which eliminates
the danger of broken jars. Hard rubber insulation at the
bottom and sides prevents electrical contact between plates
and container.

Edison batteries do not have as high capacity when new as
after some weeks of use. This is due to the improvement of
conditions in the nickel electrode, brought about by regular
charging and recharging.

The voltage of an Edison cell, when fully charged, is less than
2 volts, which is lower than in the case of the lead cell. This

246 STEAM AND GAS POWER ENGINEERING

means that more Edison cells will be required for a given voltage
than lead cells.

Ignition Dynamos. — An ignition dynamo is a miniature direct-
current generator. It has electromagnets as field magnets and
is usually of the iron-clad type. One form of ignition dynamo is
shown in Fig. 196. In using an ignition dynamo the internal
combustion engine must be started on batteries, as the speed
developed when turning the engine by hand is insufficient to
produce a spark of sufficient intensity by the dynamo. As soon
as the engine speeds up, the battery current is thrown off and the

Fig. 196. — Ignition dynamo.

spark is supplied by the ignition dynamo. Most ignition dyna-
mos will supply a spark of sufficient intensity for a make-and-
break system of ignition without an inductance coil.

Magnetos. — The magneto differs from the ignition dynamo in
that its magnetic fields are permanent magnets. For this reason
it is unnecessary to run the magneto for any length of time in
order to build up its field. Magentos can be run in any direction
and at any speed. Magnetos can be classed under two general
heads :

1. Low-tension magnetos which are used in place of batteries
or of batteries and inductance coils.

2. High-tension magnetos which generate sufficient voltage to
jump the gap of a spark plug.

INTERNAL COMBUSTION ENGINES

247

Low-tension Magnetos. — The low-tension magneto may be of
the direct-current type, in which case it differs from the ignition
dynamo in that the magnetic field is a permanent magnet; or
may be an alternating-current magneto. The alternating-current
magnetos are generally used.

Fig. 197 represents a simple type of alternating-current low
frequency magneto. It is used chiefly for the make-and-break
system of ignition and takes the place of the battery and induc-
tance coil.

Fig. 197. — Low-tension magneto.

Fig. 198. — Low-tension magneto
with circuit breaker and distrib-
utor.

The magneto illustrated in Fig. 198 is also a low-tension, al-
ternating-current magneto, differing from the preceding one in
that it has a circuit breaker and a distributor. This magneto can
be used for a jump-spark ignition system when used with a non-
vibrating induction coil.

The distributor is made use of in case of multi-cylinder engines.
The function of the distributor is to send the current to the right
cylinder at the proper time. The circuit breaker, or interrupter,
takes the place of the vibrator in the induction coil and mechani-
cally breaks the primary circuit thereby inducing a high voltage
current in the secondary circuit. The distributor is timed with the
circuit breaker and the circuit breaker is timed with the engine,
so that the hottest spark takes place at the time of ignition.

Inductor Type of Magneto. — In all of the#magnetos previously
mentioned, the armature carried the winding and has been the

248 STEAM AND GAS POWER ENGINEERING

revolving or rotating part. In the inductor type of magneto
the winding and the field magnets are stationary and the re-
volving part, which turns between the pole pieces, is made up
of a steel shaft upon which are mounted laminated iron induc-
tors. By laminated parts are meant those made up of punch -
ings of sheet iron placed side by side.

In the inductor type of magneto, all moving wires, carbon
brushes, and collector rings are eliminated. It is possible to have
inductor type of magnetos in connection with any type of igni-
tion on which magnetos are used. The oscillating magneto is
one of the inductor type and is most commonly used with the
make-and-break system of ignition. This magneto gets its name
from the fact that the moving part does not revolve through a
complete circle, but merely oscillates through a very few degrees.
The rapid separation of the points is caused by strong springs
attached to the arms situated near the end of the rotor shaft.
As the spring snaps the inductor back the current is generated
and at the same time the igniter points within the cylinder are
very quickly separated, producing the spark.

High-tension Magnetos. — A high-tension magneto differs
from a low-tension magneto in that it can generate a high voltage
current without the aid of an induction coil. Fig. 199 illustrates
a high-tension magneto all the parts of which are named. Both
the primary and secondary windings are wound on the same core.
In the armature type, both windings are on the armature and
revolve with it, while in the inductor type both primary and sec-
ondary windings are on the stationary coil between the pole pieces.

In the armature type, the armature carries a primary winding
of a few turns of fairly large insulated copper wire and a large
number of turns of very fine insulated copper wire. The con-
denser is also carried in the armature. The interrupter or
circuit breaker of a high-tension magneto is usually mounted on
the end of the armature shaft and revolves with it. The
high-tension current is taken from the armature by a brush and
collector ring. The interrupter also acts as a timer and breaks
the primary circuit at the proper time. This breaking of the
primary circuit induces a high voltage current in the secondary
exactly in the same .manner as the vibrator did in the induction
coil, previously discussed.

INTERNAL COMBUSTION ENGINES

249

Due to the fact that the windings are revolving, there is a
generative as well as an inductive effect. This generative effect
prolongs the duration of the spark which would be of very short
duration with the inductive effect alone. The cams must be
so arranged that the primary is broken at approximately the time
when the voltage is at a maximum, which is when the armature
core is removed from the field.

Longitudinal Section.

Rear View.

1. Contact plate. 8. Contact piece. 14. Brass end cap.

2. Slip ring with distributor segment. 9. Fastening screw for contact 15. Flat spring.

3. Carbon. breaker. 16. Bolt for spring 15.

4. Carbon holder. 10. Timing lever. 17. Condenser.

5. Contact-breaker disc. 11. Steel segment. 18. Dust cover.

6. Bell-crank lever. 12. Sheet-circuiting screw. 19. Short platinum screw.

7. Bell-crank lever spring. 13. Flat spring for timing lever. 20. Long platinum screw

Fig. 199. — High-tension magneto.

A safety gap is provided in high-»tension magnetos to protect
the secondary winding. This is simply an air gap across
which the current may jump in case of a break in the secondary
winding. Without the safety gap the insulation of the secondary
would be in danger of being punctured by the high voltage
current in case of a break or loose connection.

If more than one cylinder is to be served, a high-tension mag-
neto carries a distributor which distributes the current to the
proper cylinder.

Fig. 200 illustrates a typical wiring diagram of a high-tension
magneto of the armature type.

Timer and Distributor Systems. — With multiple cylinder
engines a timer is often used in connection with vibrating indue-

250 STEAM AND GAS POWER ENGINEERING

tion coils. The function of the timer is to complete the primary
circuit at the proper time for each cylinder thereby causing the
vibrator to function resulting in a hot spark at the spark plug.

Condenser
Fig. 200. — Wiring diagram for a high-tension magneto.

One type of timer, illustrated in Fig. 201, is used on a four-cylin-
der engine. E represents the segments in the housing S. These

Fig. 201. — Timer.

segments are electrically insulated from each other with fibre
or some other insulating material. R is the revolving arm for
closing the circuit at the proper time.

INTERNAL COMBUSTION ENGINES

251

The distributor system of ignition is very common practice on
multiple cylinder high-speed engines. In this system the dis-
tributor and circuit breaker are mounted on one shaft. This
shaft has projections or in some cases indentations equally spaced
and corresponding to the number of cylinders to be served.
These projections or indentations act as cams for interrupting
the primary circuit. A condenser is usually placed across the
breaker points to prevent sparking at the points. In connection
with this system a non-vibrating induction coil is usually used.
One end of the secondary is usually grounded, while the other

._ &£ounof± L-L-JL-JUJ

Fig. 202. — High-tension distributor system.

leads to the center post of the distributor. The distributor
then conducts the secondary to the proper cylinder at the proper
time.

Fig. 202 represents a high-tension distributor system em-
ploying a timer and vibrating induction coil.

In most distributor systems a circuit breaker takes the place
of both timer and vibrator so that a non-vibrating induction coil
can be used.

Governors

Every internal combustion engine must be provided with a
governor in order that its speed may be kept constant as the
power developed by the engine varies. Stationary engines are

252 STEAM AND GAS POWER ENGINEERING

usually mechanically regulated, the governor being operated by
the speed variations of the engine. Motor vehicles are generally
hand-governed, but are often equipped with a limit governor
to prevent overspeeding. The speed regulation of internal com-
bustion engines is accomplished by one of the following methods :
hit-and-miss system, varying the quality of the mixture, varying
the quantity of the mixture, varying the time of ignition, and
combination systems.

Hit-and-miss Governing. — In this system the number of explo-
sions is varied according to the load of the engine. When the
engine is running at full load the explosions follow each other in
regular order until the speed has increased enough above the
normal to cause the governor to act, preventing the drawing in
of the next charge, thus missing an explosion. This is followed
by the slowing down of the engine, which causes the explosions
to recur.

The hit-and-miss system can be carried out in several ways de-
pending upon the valve gear of the engine.

In the case of small engines, where the inlet valve is operated
automatically by the suction of the piston, the governor acts by
keeping the exhaust valve open, thus preventing the spring-loaded
inlet valve from opening.

When the inlet valve is mechanically operated from the valve
gear shaft, the governor acts directly on the inlet valve by with-
drawing a trigger, called a pick-blade, or a cam-roller in the valve
actuating mechanism, thus preventing the admission of a new
charge at light loads.

The hit-and-miss system can also be operated by keeping the
fuel valve closed so that the engine draws in only air at light loads.

The governor proper in connection with the hit-and-miss sys-
tem is usually some form of fly-ball governor.

The hit-and-miss system of governing is very simple and gives
good fuel economy at variable loads. As the explosions in the
engine cylinder do not occur at regular intervals, this system of
governing necessitates the use of very heavy fly-wheels in order
to keep the speed .fluctuations within practical limits. The hit-
and-miss system is satisfactory for small engines where close
speed regulation is not essential, but is not practical in connection
with engines which must operate at nearly constant speed.

INTERNAL COMBUSTION ENGINES 253

Quality Governing. — In this system the number of explosions
per minute and the quantity of the mixture admitted to the
cylinder remain constant, but the quality of the mixture, that is,
the ratio of fuel to air, is varied according to the load. This is
accomplished either by the governor controlling a throttle or a
cut-off valve in the gas supply pipe. The inlet valve which ad-
mits the mixture to the engine cylinder opens under all load con-
ditions to its full lift, admitting to the cylinder a mixture of the
same volume at different loads. The governor controls both the
air and gas openings, increasing the air supply at light loads in the
same proportion as the amount of gas is decreased.

This method of governing retains the same compression pres-
sure at all loads, but the fuel economy decreases very rapidly as
the load drops, as weak mixtures are difficult to ignite and are
slow burning.

Quantity Governing. — In the quantity governing system the
proportion of air to fuel remains constant, but the speed regula-
tion is accomplished by altering the quantity of the charge admit-
ted to the cylinder at variable loads. This system of governing
can be carried out by the use of a butterfly valve under the control
of the governor, which throttles the charge in a manner similar
to the throttling steam engine. By another method, call-
ed the cut-off method, the inlet valve is held open only during
a portion of the suction stroke, and is suddenly closed at a point
determined by the governor and suitable to the load. The cut-
off method of quantity governing is similar in its action to the
governor in connection with automatic cut-off steam engines,
such as the Corliss.

Combination Systems. — A combination of the hit-and-miss and
the throttling regulating systems has been tried. The throttling
constant quantity system is used for loads above one-half the
rated load of the engine, whereas the hit-and-miss system is em-
ployed for loads below one-half. Another combination governor
uses quality governing at heavy loads and quantity governing at
light loads. These combination systems have been designed to
utilize the advantages of the several systems, but are complicated
and are used only in special cases.

254 STEAM AND GAS POWER ENGINEERING

Mufflers

An exhaust muffler is generally used to silence the noise inci-
dental to the escape into the air of the exhaust gases from an
internal combustion engine. In some installations mufflers are
also used for the air intakes of large engines.

Exhaust mufflers vary greatly in design, but are intended to
silence the exhaust noise by reducing the velocity of the exhaust
gases to a minimum, without appreciably increasing the back
pressure.

In some cases, the muffler is an enlarged exhaust pipe or a vessel
of suitable volume to permit the gradual expansion of the exhaust
gases. Some mufflers are provided with baffles and other ob-
structions to reduce the velocity of the exhaust gases. In other
cases, sprays of water have been employed in connection with
mufflers, to reduce the velocity of the gases by cooling. The
use of water is effective, but should not be employed if the exhaust
gases contain sulphur compounds.

A muffler should have sufficient volume in order to throw little
back pressure on the engine, should be strong enough to stand the
strain of an explosion, which may result from the presence of
unburned gases in the exhaust, and should be constructed so that
it can be readily taken apart for inspection, cleaning and repair.

The exhaust gases from an internal combustion engine should
never be allowed to escape into a chimney or into a sewer, as an
explosion due to the accumulation of unburned gases may occur
at any time.

Problems

1. Examine some float feed carburetor and hand in report showing how
these carburetors differ from those described in the text. Clear sketches,
showing fundamental details of construction, should accompany report.

2. Examine some magneto and hand in a report which will illustrate and
explain its construction.

3. Show by means of clear sketches the details of a hit-and-miss governor
and also of a governor of the throttling type.

4. Examine the lubricators in use on various stationary internal combus-
tion engines and report in which respects these differ from lubricators for
steam engines.

5. Make clear sketches of mufflers suitable for small and for large station-
ary internal combustion engines.

CHAPTER XIV
GAS POWER PLANT TESTING

The testing of internal combustion engines operating upon
gaseous or liquid fuels is similar to the testing of steam engines,
at least in the more important details. The heat supplied to the
engine by the fuel and the delivered power are the two main
points to be investigated. Indicators cards may be used to
determine the inner workings of the cylinder and in measuring
the indicated horse power. The amount of heat absorbed by
the jacket water can be determined by weighing the amount of
water passing through the jacket and taking the temperature
of the inlet and outlet water.

Measurement of Fuel Used. — When the fuel used is in a
gaseous state, the volume used is usually measured by some form
of gas meter. Most commercial meters give a fair degree of
accuracy, but they should be calibrated under the conditions to
which they are subjected during the test. Venturi meters
(Chapter X) are used when the volume of the gas to be measured
is large.

When liquid fuels are used the amount supplied the engine
is best measured by means of small platform scales. One method
consists in placing a supply tank or reservoir upon the scales,
using a flexible connection from the tank to the carburetor. The
difference in the weight of the fuel at the beginning and at the
end of the test gives a direct measure of the quantity of fuel used.
The flexible connection between the tank and engine is best made
of flexible metallic tubing having no rubber insertions. Rubber
tubing is acted upon by petroleum fuels and is soon destroyed.

Many internal combustion engines are equipped with an over-
flow type of carburetor, in which a constant quantity of fuel is
maintained in the carburetor by supplying a larger quantity of
fuel than is necessary, while the excess is drained through an
overflow pipe. In this case the method of weighing the fuel is
much the same as that just explained, with the exception that the

255

256 STEAM AND GAS POWER ENGINEERING

fuel from the overflow is collected in a separate vessel and is
either returned to the main fuel tank before the final weighing at
the end of the test or is weighed separately and the amount
deducted from the weight as determined from the main tank.

Instead of measuring the fuel by weighing, measurements by
volume are sometimes used. In that case a cylindrical vessel of
small diameter is equipped with a gage glass. The vessel is
calibrated by filling the tank to various heighths and by deter-
mining the corresponding weight of fuel per inch of height. The
fuel supplied to the engine during the test is then indirectly
measured by noting the difference of the fuel level in inches and
converting it into pounds from the calibration data. Such a
method is not considered accurate because of the change of
volume of the fuel with the change of temperature. For accurate
results the method of direct weights should be used.

Heat Consumption of the Engine. — The heat consumption of
the engine, or the heat supplied by the fuel, is found in the case of
gaseous fuels by multiplying the heat of combustion of one cubic
foot of the fuel, as determined by calorimeter test, by the volume
of the gas consumed in cubic feet. For liquid fuels the heat
consumption is equal to B.t.u. per pound of fuel multiplied by the
weight of fuel used in pounds.

Brake Horsepower. — The brake horsepower, or the delivered
horse power, of an internal combustion engine is usually measured
by means of a Prony brake. Other types of dynamometers, as
explained in the measurement of the delivered power of the steam
engine (Chapter X), could also be used.

When a Prony brake is used the power is calculated by the
formula:

-r. , 2-n-lwn

Rhp- = 33000

In which t = 3.1416

I = length of brake arm in feet.
w = net weight as measured by the scale upon

which the brake arm rests.
n = number of revolutions per minute.

Indicated Horsepower. — The indicated horsepower of an
internal combustion engine is measured in practically the same

GAS POWER PLANT TESTING 257

manner as in the case of steam engines, but with the following
differences: Ordinary types of steam engine indicators are not
well adapted to the testing of gas engines. The pressures
exerted in the gas engine cylinder are usually higher than
those common in steam engines and are more suddenly applied.
In order to withstand these stresses the steam engine indicator
would have to be equipped with a comparatively strong spring.
The piston of the gas engine indicator is usually made J"2 the area
of that of the steam engine indicator piston and the springs are
interchangeable. Thus a 100 pound steam indicator spring
when used with a gas engine indicator would produce a one-
inch vertical movement of the pencil for a pressure of 200 pounds.

In calculating the indicated horsepower, it must be remem-
bered that the complete cycle is not produced at every revolution
and it is the number of explosions rather than the number of
revolutions that determines the horse power.

The formula for calculating the indicated horsepower becomes :

Lhp- = 3^000

In which

p = mean effective pressure in pounds per square inch as deter-
mined from the indicator card.

I = length of the engine stroke in feet.
a = area of the piston in square inches.

e = number of explosions per minute.

The Measurement of the Heat Absorbed by the Jacket Water.

The heat absorbed by the jacket water is calculated by the
formula :

W(t2-h)
In which

W = the weight of water passing through the jacket in a

unit of time.
12 = the temperature of water discharged from the jacket.
t\ = the temperature of the inlet water to the jacket.

The weight of the jacket water is best measured by the use of
one or more tanks placed upon platform scales. During the
test these tanks are alternately filled, weighed, and emptied.

258 STEAM AND GAS POWER ENGINEERING

Duration of Test. — When the load upon a gas or oil engine is
nearly constant, and can be maintained so for an appreciable
period, the duration of the test need not be more than about one
hour. When the load fluctuates, longer periods are necessary
for accurate results.

Starting the Test. — Before starting a test upon a gas or oil
engine sufficient time should be allowed for conditions to become
constant. The engine should be operated at the prescribed load
until all parts are thoroughly heated. At a certain predeter-
mined time the test is started and the regular measurements and
observations are made until the test is closed.

Gas Producer Testing. — To ascertain the efficiency of a gas
producer the following data must be obtained: the quantity of
fuel used, the amount of gas generated, the heat of combustion of
the fuel, and the heat of combustion of the gas.

The heat of combustion of the fuel and of the gas can be
determined by means of the calorimeters explained in Chapters II
and XII respectively.

To determine the amount of fuel used, the length of the test
should be such that the total consumption of the fuel should be at
least ten times the weight of fuel contained in the producer during
normal operation. Producer tests of short duration are inaccu-
rate. The fuel used is weighed on platform scales.

The amount of gas generated is determined by means of a
Venturi meter, Pitot tube, or some other gas meter of special
design.

In a complete test the amount of power required for driving
the fans and other auxiliaries is determined, as well as the amount
of steam used and the final purity of the gas.

A. S. M. E. Code. — Complete and more detailed instruction
concerning the testing of Gas Power Plants will be found in the
Rules for Conducting Performance Tests of Power Plant Apparatus,
published by the American Society of Mechanical Engineers.

Problems

1. Determine by test the amount of fuel used by an internal combustion
engine per brake horsepower per hour.

2. Compare the heat consumption in B.t.u. of the following engines per
brake horsepower per hour:

GAS POWER PLANT TESTING 259

(a) Gasoline engine which delivers a brake horsepower per hour for one-
tenth of a gallon of gasoline.

(b) Producer gas plant which consumes 1M pounds of anthracite coal per
B.hp.

(d) Alcohol engine which consumes one pound of alcohol per B.hp.

3. Compile from the Power Test Code of the American Society of Mechan-
ical Engineers a table suitable for taking data in connection with a complete
test on a gas producer plant.

CHAPTER XV
LOCOMOTIVES

The Locomotive Compared with the Stationary Steam Power
Plant. — On account of requirements which must be met in each
case, the locomotive and the stationary steam power plant differ
in construction. The stationary power plant has practically
unlimited space available. The locomotive is limited in width
by the gage of the track, and by the clearance required for
station platforms and passing trains; it is restricted in height by
the clearance of bridges and tunnels; the sharpness of the curves
limit its length, and its weight is practically fixed by the strength
of bridges and by the type of road bed. To develop the variable
power demands to which locomotives are subjected, the boiler
must contain ample heating surface and at the same time must
occupy small space. The rate of combustion must be forced to
the extreme, as the grate surface is limited in width by the allow-
able road clearance and in length by the distance a fireman can
spread the coal. In stationary plants 10 to 20 pounds of coal
are ordinarily burned per square foot of grate surface when
operated with natural draft; in locomotive practice, by the use
of artificial draft 150 pounds or more are usually burned per
square foot of grate surface.

Space limitations on locomotives prohibit the use of fans or of
high stacks for the production of draft, and an induced draft
created by the exhaust steam must be used. This practice
prevents the operation of the engine condensing and makes diffi-
cult the use of the exhaust steam in connection with feed water
heaters.

The Essential Parts of a Locomotive. — The essential parts of
a locomotive are illustrated in Fig. 203. The boiler (1) consists of
a cylindrical shell, closed at its two ends by tube plates which are
connected below the water level by numerous fire- tubes (3).

The furnace, or fire-box (2), is an extension of the boiler shell,
the sides of which extend downward, forming a chamber sur-

260

LOCOMOTIVES 261

rounded at the top and at the bottom by water. The bottom
of the fire-box is fitted with a grate (24) upon which the fuel
is burned. Below the grate is an ash pan (28) which retains
the ash until such a time as it may be removed. An opening
at the back of the fire-box serves as a fire-door (23).

The furnace gases pass through the fire-tubes and enter the
front-end or smoke box (4). In entering the smoke box, the
gases are deflected downward by the diaphragm or deflector plate,
thence through the spark-arrester netting (15), after which they
mingle with the exhaust steam entering the smoke box from the
exhaust pipe (11), and pass out the stack (5). Accumulation of
cinders is removed from the smoke box through the spark chute
(12), cleaning tools being inserted through the spark clean-
ing hole (13). Access to the smoke box is made through the door
(17), or the entire smoke box cover (16) may be removed.

Steam from the boiler enters the steam dome (6) from which it
passes to the engine cylinder. The throttle lever (8), which
controls the valve in the throttle chamber (7), is used to regulate
the quantity of steam entering the cylinder.

The steam after passing through the throttle valve enters the
dry pipe (9) which passes through the steam space and absorbs a
certain amount of heat from the steam with which it is in contact.
Upon reaching the smoke box the dry pipe terminates in a tee
from which two steam pipes (10) are used to direct the steam into
the two cylinders.

The two cylinders are on the opposite sides of the locomotive
and the cranks are separated 90 degrees. Considering only one
cylinder, the steam enters through the valve (36) and after
performing its function it passes through the exhaust pipe (11)
and is further utilized in creating the draft. When the engine
is running the exhaust causes a constant movement of air through
the furnace and tubes .

The reversing of the engine, as illustrated in Fig. 203, is accom-
plished by the use of the Walschaert valve gear (see Chapter V) .
The reversing lever (54) is located in the engine cab. The reach
rod (55) connects the radius rod (49), thus giving a means for
controlling the position of the link block with respect to the link
(48) and thereby controlling the position of the valves and the
direction of the engine. The motion of the link is obtained from

262 STEAM AND GAS POWER ENGINEERING

LOCOMOTIVES 263

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the eccentric crank arm (46) and the additional motion from the
lap and lead lever (50), as shown in the illustration.

The injector (105) admits water to the boiler. Sand stored
in the box (91) is delivered to the rails through the sand pipes
(92) when it is necessary to increase the adhesion of the drivers.
Air pumps (83) deliver air to the braking system, while such parts
as the bell (90), whistle (19), safety valve (22), and the head
light (86), need no explanation.

Early History of the Locomotive. — Locomotives, if they may
be designated by such names, were built prior to 1825, although
in that year George Stephenson is credited with the first locomo-

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Fig. 204.— The locomotive of 1832.

tive. Stephenson's " Rocket " was of foreign make, had cylinders
8 in. by 16% in., weight about 4 tons, and was capable of making
29 miles per hour.

In the United States "The Old Ironsides," built in 1832 was
one of the first locomotives. As illustrated in Fig. 204, this was
a four-wheeled machine; it weighed about 5 tons and was capable
of operating at a speed of about 30 miles per hour.

The modern locomotive is a development of the above types.
Its improvements paralleled the practice in steam-power engi-
neering.

Classification of the Locomotive. — Several methods for the
classification of locomotives are in general use. One method

LOCOMOTIVES

265

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quite commonly used is based upon the wheel arrangement.
This system indicates the number of truck, driving, and trailer
wheels. Thus a 262 type would signify a machine having a
two-wheeled front truck, 6 drivers, and a two-wheeled trailing
truck. Table 8 gives the wheel arrangement, the designating
name, and the numerical symbol of the various types of locomo-
tives.

The Development of the Locomotive. — The development of
the locomotive to its present state has resulted from the demands
for machines of larger haulage capacity. The greatest difficulty
found was in securing the larger boiler and grate areas which were
necessary. The method by which these features were met is
best illustrated by considering those types of locomotives which
were especially designed for passenger traffic.

The American type, or the eight wheel, 440, was once con-
sidered the standard locomotive for passenger service, while at
the present time its use is confined to light service.

The Atlantic type, 442, was developed from the American
type, and in general the difference between the two types is the
addition of a trailing truck. By this design the boiler-heating
surface could be enlarged, while the use of the trailing truck
rather than another set of drivers made space for the necessary
additional fire-box capacity.

The Pacific type, 462, is the development of the Atlantic
type using the same general design. The insertion of an addi-
tional driver is to distribute the weight by not having it concen-
trated upon two drivers, thereby increasing the rail contact and
the amount of adhesion.

The Mallet Articulated Compound. — The need for larger
powered locomotives and trie limiting conditions to which the
locomotive in its construction is subjected leaves practically but
one course to follow if any increase in capacity is to be made and
that is by increasing the number of drivers or the length of the
engine. To increase the length and maintain a rigid type was out
of the question on account of the difficulties and dangers in
rounding curves.

The articulated compound locomotive, illustrated in Fig. 205,
has been designed to meet the above conditions. This type
consists of two sets of engines under one boiler. The rear set

LOCOMOTIVES

267

is fixed rigidly to the boiler while the front set supports the
overhanging end of the boiler and is capable of adjusting itself
to the alignment of the road. The two sets of engines are hinged
together and exhaust pipes from one set of cylinders to the other
are made flexible by ball and socket joints. The steam from the
boiler enters the high pressure cylinders and exhausts into the
low pressure cylinders, which are located on the front engine, from
which the steam exhausts as is the case in other types.

The most powerful locomotives are of the articulated type.
While little used at the present time in passenger service, they
have been very satisfactory in heavy freight service especially
on roads having heavy gradients combined with sharp curves.

Fig. 205. — Articulated compound locomotive.

Locomotive Superheaters. — Two types of superheaters are
used in locomotive practice: one receives its heat wholly from
the gases in the smoke box, the other receives part of its heat from
the smoke box, but the greater amount of heat is derived from
superheater elements extending into the tubes.

The smoke box type is constructed wholly within the smoke
box, requiring little or no change in the usual boiler arrangement,
but has the disadvantage of being limited to low degrees of super-
heat. It consists of two small cast steel drums connected to
each of the steam pipes, while numerous small tubes complete
the path of the steam. The steam entering the upper drum
passes through the tubes and absorbs heat from the flue gases
which surround them.

One type of locomotive superheater is illustrated in Fig. 206.
As usually constructed this superheater consists of a box or
header A located in the smoke box to which are attached
numerous superheating elements. These elements are con-

268 STEAM AND GAS POWER ENGINEERING

structed of seamless steel tubing and return bends, and are
located in large fire-tubes C through which the furnace gases
pass. The steam is thus made to pass through a superheating
element before entering the cylinder. The flow of gases over
the superheater surface is controlled by a damper D which is
operated by the cylinder E. When the engine throttle is closed
the damper is similarly closed, thus protecting the superheater
tube. When the throttle is opened and steam is passing through
the superheater, the damper is automatically opened.

Fig. 206. — Locomotive superheater.

Locomotive Stokers. — Many different designs of stokers have
been applied to locomotives. The chief advantage in the use of a
mechanical stoker lies in the facility for the burning of a greater
amount of coal and in the possibility of using cheaper fuels than
is possible with hand firing.

Fig. 207 illustrates one type of locomotive stoker suitable for
nut and slack coal. It consists of a screw conveyor placed under
the floor of the tender and three distributing nozzles for spraying
the coal over the fire.

Coal from the tender passes first through regulating screens,
thence by a screw conveyor to the engine cab, and is finally deliv-

LOCOMOTIVES

269

ered to the distributing nozzles from which it is fed to the furnace
by means of a steam blast. Of the three distributing nozzles
shown the central one utilizes the fine coal and feeds the center
of the furnace. The remaining two are supplied with coarser
coal and feed the two sides of the furnace.

Fig. 207. — Locomotive stoker.

Draft Appliances. — A typical front-end is illustrated in Fig.
208. The exhaust steam from the cylinders passes through the
exhaust ports into the exhaust pipe E, which terminates in a
restricted area or exhaust tip. This arrangement regulates the
velocity of the exhaust and the intensity of the draft. A small
opening creates an intense draft, but at the same time raises the
back pressure in the cylinder. The nozzle is arranged so that

270 STEAM AND GAS POWER ENGINEERING

sufficient draft is obtained and the back pressure in the cylinders
is as low as possible.

The stack extension or " Petticoat Pipe/' P, is used when the
exhaust nozzle is low. This is used as an additional channel to
conduct the steam which, if not used, would fill the smoke-box,
thus destroying the draft. The diaphragm D begins above the
top row of tubes and terminates in a movable slide S, which may
be raised or lowered to meet varying conditions. The diaphragm
acts first to deflect the solid particles in the gases downward and
second as a draft regulating device. Without the diaphragm
the upper rows of tubes would be greatly affected by the exhaust.
This would produce uneven burning of the fuel over the surface

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Fig. 208. — Locomotive front end.

of the grate. By regulating the diaphragm the draft can be
made uniform over the entire grate surface.

Injectors. — The injector as a means of introducing feed water
into a boiler is seldom used in stationary power plant practice.
It is the general impression that the injector is not as reliable as
the reciprocating pump and in addition cannot pump hot water.
Its chief advantage is due to the small space it occupies and this fact
makes it practical for use on locomotives, where space economy
is important. To overcome the possibilities of failure to operate,
locomotives are equipped with two injectors. If one injector
becomes inoperative the other may be relied upon.

Air Brakes. — One of the first types of air braking systems was
what was generally known as the Straight Air Brake. This con-
sisted of a steam driven air pump located on the engine, a reservoir

LOCOMOTIVES

271

272 STEAM AND GAS POWER ENGINEERING

in which compressed air was stored, a pipe line extending through-
out the length of the train, each car being connected by flexible
hose couplings, and a brake cylinder on each car the piston of
which was directly connected to the brake levers. The engineer's
valve could admit air to the piping and^thence to the cylinder
causing the brakes to act, or could discharge the air from the
braking system or train line, thus releasing the brakes.

Experience demonstrated that the use of the straight air brake
system is dangerous when used on trains. The hose connection
between cars often broke resulting in the loss of the braking effect
throughout the entire train. When the train would brake apart
the rear part often overtook that of the front with the possibility
of a serious collision and damage. It was found necessary to
have an automatic system and this led to the introduction of
the indirect or automatic system which is still used.

The automatic system operates by decreasing the air pressure
in the train line rather than by increasing it as in the case of the
direct air system. A diagrammatic layout of an automatic system
is illustrated in Fig. 209. A compressor delivers air to a main
reservoir which is connected through the engineers valve to the
train line. Under each car is another reservoir, termed the
auxiliary reservoir, a brake cylinder and triple valve controlling
air to and from the brake cylinder.

When the engine is coupled to the train, air is admitted to the
train line, passes through the triple valve, and enters the auxil-
iary reservoir. When air is released from the train line, the
lowering in pressure causes the triple valve to operate permitting
the air in the auxiliary reservior to be transferred to the brake
cylinder, thus the brakes are applied. In this system if a coup-
ling hose should burst or the train part, the brakes would be set
because of the lowering of the pressure in the train line.

Problems

1. In which respects does the locomotive power plant differ from the
ordinary stationary steam power plant?

2. Ascertain what reversing mechanism is used on the locomotives passing
through your city.

3. Compare the air-brake system used on electric street cars in your city
with the automatic air brakes as used on locomotives.

CHAPTER XVI
AUTOMOBILES, TRUCKS AND TRACTORS

Automobiles

Types of Automobiles. — Automobiles are propelled by internal
combustion engines, by steam engines, or by electric motors with
current secured from storage batteries.

At the present time a very large majority of automobiles are
driven by internal combustion engines using gasoline as fuel.
The gasoline automobiles possess the following advantages : they
are manufactured in many different types and designs, can be
secured at a wide range of prices, are more economical than other
types, and are usually provided with a fuel storage of sufficient
capacity to propel the car several hundred miles. The disadvan-
tages of the gasoline automobile are that it is not self -starting,
lacks over-load capacity, and must be built with a complicated
system of gears for speed changing and for reversing.

The automobile propelled by a steam engine is very flexible,
is easily controlled, and has a very large range of power. To off-
set these advantages, the steam automobile requires considerable
time to start after a long stop, as steam must be generated in the
automobile boiler before the engine will start. This fault is
being greatly remedied in some of the recent steam automobiles,
but all steam automobiles require considerable skill in opera-
tion, as constant attention must be given to the fuel and water
supply.

The electric automobile is also very flexible, operates more
quietly than other types, is clean, and is easy to start and to con-
trol. The greatest disadvantage of the electric car is that it
can run only for short distances without recharging its storage
batteries. The use of the electric automobile is limited mainly
to cities where facilities are available for charging storage bat-
teries. Electric cars are also expensive to operate.

As steam and electric automobiles are not generally used, this
chapter will deal only with the gasoline automobile,
is 273

274 STEAM AND GAS POWER ENGINEERING

Essential Parts of a Gasoline Automobile. — The essential parts
of a gasoline automobile are :

1. A power plant, which consists of an internal combustion
engine and its auxiliaries, such as the fuel system, carburetor,
ignition system, and cooling and lubricating systems. In some
cars this also includes the starting equipment.

2. Friction clutch, for disengaging the engine from the pro-
pelling mechanism.

3. Transmission mechanism for speed changing and reversing.

4. Differential gear, the purpose of which is to allow one drive
wheel to revolve independently of the other, this being necessary
when turning corners.

5. Front and rear axles.

6. The frame for supporting the power plant, the transmission
system, and the body of the car. Interposed between the body
and the axles are the springs, which are built up from a number of
leaves.

7. Control system, which includes the steering mechanism,
hand levers and foot-pedals, means for controlling the spark
position, the carburetor throttle, the clutch, the transmission
gearing, and the brakes.

8. Wheels, tires, lights, alarm, body, top, fenders, dash, run-
ning board, wind shield, and speedometer.

The term chassis is applied to the car with the body and acces-
sories removed.

Automobile Motors. — Modern automobiles use four, six, eight,
or twelve-cylinder motors. The motors are all of the vertical
type and operate on the Otto four-stroke cycle. The engine is
mounted in the front end of the car for accessibility, and also
for the purpose of more evenly distributing the weight of the car.
Multi-cylinder motors permit of easier starting, operate more
smoothly, run with less vibration, and have a wider range of
power. Four and six-cylinder engines have all cylinders in one
row and located on one side of the crankshaft. Eight-cylinder
engines have their cylinders V-type in two rows with the rows
set at an angle of 90 degrees. Twelve-cylinder engines are of the
V-type and have two rows of cylinders set at an angle of 60
degrees.

The cylinders may be cast singly or en-bloc; the en-bloc con-

AUTOMOBILES, TRUCKS AND TRACTORS 275

struction means that several cylinders are cast in one piece. The
single-cylinder casting is light in weight and is easily replaced.
The en-bloc motor is more rigid, occupies less space and is the
more commonly used.

Cooling of Automobile Motors. — Automobile motors are gener-
ally water-cooled and are provided with radiators for the purpose
of cooling the water after it has absorbed heat from the cylinder
walls. Either the thermosyphon or the forced water circulation
system is used.

Fig. 210. — Thermo-syphon water-circulation system.

The thermo-syphon system (Fig. 210) depends upon the fact
that water rises when heated. This system does not require a
pump to circulate the water. The water enters the cylinder
jackets at A (Fig. 210). Upon becoming heated by the explo-
sions going on within the cylinder of the engine, the water rises
to the tops of the cylinder jackets, entering the pipe B and passing
into the radiator at C where it is brought into contact with the
radiator cooling surfaces. On being cooled, the water becomes
heavier and sinks to the bottom of the cooling system, to enter
the cylinder once more and to repeat its circulation. The cooling
action of the radiator is increased by the fan F which draws air
through the radiator spaces.

276 STEAM AND GAS POWER ENGINEERING

The forced circulation cooling system differs from the thermo-
syphon system in that it has a circulating pump to aid in the
circulation. The pump which is usually of the centrifugal type
makes the circulation more positive. The course taken by the
circulating water is exactly the same in both systems.

Some air-cooled automobile motors have proven very satis-
factory. The cylinders of air-cooled motors are ribbed to increase
the radiating surface and the circulation of the air is produced by
means of a fan located in the motor fly wheel.

Lubrication. — Five methods are used for lubricating automobile
motors :

1. The splash system. This system depends entirely upon
dippers on the connecting rods to splash the oil to the various
parts of the motor.

Fig. 211. — Motor with poppet valves.

2. The circulating splash system. This differs from the
straight splash method in that a pump at a low point in the crank
case delivers the oil to troughs under the connecting rods. From
these troughs the dippers splash the oil in the same manner as
in the straight splash system.

3. The forced splash system. This system uses a pump to force
the oil to the main bearings and to the troughs previously men-
tioned. Dippers on the connecting rods then splash the oil in
the same manner as mentioned before. This system differs from
the circulating splash in that the oil is forced to the main bearings.

4. The forced system. This system has a hollow or drilled
crankshaft through which the oil is forced from the main bearings

AUTOMOBILES, TRUCKS AND TRACTORS 277

to the connecting-rod bearings and is then splashed to the wrist
pin and cylinder walls.

5. The full forced system. This system has tubes leading up
along the connecting rods to the wrist pin. The oil is forced

1. Cylinder.

2. Water-jacketed cylinder

head.

3. Spark plug.

4. Inner sleeve.

5. Outer sleeve.

6-7. Port openings in sleeves.

8. Priming cup.

9. Oiling grooves in sleeves.

10. Port opening in cylinder.

11. Connecting-rod operating

outer sleeve.

12. Connecting-rod operating

inner sleeve.

13. Fly wheel.

14. Oil trough adjusting lever

connected to throttle.

15. Lower part of crank case,

containing oil pump,
strainer and piping.

16. Oil scoop.

17. Adjustable oil troughs.

18. Crank shaft.

19. Crank-shaft bearing.

20. Starting clutch.

21. Silent chain drive for
magneto shaft.

22. Silent chain driving sprock-

et for electric generator
(on 4-cylinder models).

23. Silent chain drive for

eccentric shaft.

24. Eccentric shaft.

25. Connecting rod.

26. Bearing for eccentric shaft.

27. Piston.

28. Piston rings.

29. Cylinder- head ring (junk

ring) .

Fia. 212. — Sectional view of Sterns-Knight four-cylinder motor.

by the pump to the main bearings, thence through the crank-shaft
to the connecting-rod bearings, thence through the tubes to the
wrist pin, and through the hollow wrist pin to the cylinder walls.
With a full-forced system a relief valve is provided to prevent the
oil pressure from becoming excessive.

278 STEAM AND GAS POWER ENGINEERING

The parts of the automobile motor which require lubrication
are the main shaft bearings, crank-pin bearings, wrist-pin bear-
ings, cam shaft bearings, timing gears, cams, cam lifter guides,
cylinder walls, and other moving parts, such as yokes and ends
of rods.

Automobile Valves. — The poppet type of valve, Fig. 211, is
generally used on automobile motors. The sleeve valve type of
motor (Fig. 212) is also used on certain designs of automobiles.

Poppet valve motors are built in several forms according to
location of valves.

Fig. 213. — Ell-head cylinder. Fig. 214.

-Tee-head cylinder. Fig. 215. — Valves-in-the
head cylinder.

1. The ell-head motor (Fig. 213) has both the intake and
exhaust valves on one side of the cylinder.

2. The tee-head motor (Fig. 214) has the exhaust valves on
one side of the cylinder and the intake valves on the other.

3. The valve-in-the-head or I-head motor (Fig. 215) has
both intake and exhaust valves in the cylinder head.

4. The combination ell-head and valve-in-head, sometimes
known asF-head, has the intake valve in the head and the exhaust
valve on the side of the head.

AUTOMOBILES, TRUCKS AND TRACTORS 279

Clutches. — The clutch is a device used for connecting the
engine to, and disconnecting it from, the propelling gear of the
car. Clutches depend upon the frictional adhesion between
surfaces and are of two general types.

1. The cone clutch, illustrated in Fig. 216, consists of a leather-
faced cone C which is pressed by the spring S against the inside of
the tapered rim of a fly wheel W.

Fig. 216. — Cone clutch.

2. The multiple disk clutch (Fig. 217) depends for its action
upon the friction between disks. Alternate disks are fastened
to the driving and driven parts. The disks marked A are fas-
tened to the engine shaft and those marked B connect with the
mechanism to be driven. If the clutch runs in a bath of oil it is
called a wet-disk clutch. A spring is employed to hold the disks
in contact when the clutch is in action.

280 STEAM AND GAS POWER ENGINEERING

Transmissions. — The speed of an internal combustion engine
and its direction of rotation cannot be varied to meet the re-
quirements of an automobile. This necessitates the introduction
of some form of mechanism for speed changing and also for re-
versing, in order that different speed ratios and reversal of direc-
tion can be secured between the engine and the drive axle. The
mechanism, which is used in speed changing and in reversing,
is known as the transmission. The transmission is so constructed
that the propelling ability of the motor is increased at the expense

Fig. 217. — Multiple-disk clutch.

of the speed of the automobile. That is, the motor through the
gear ratios of the transmission is able to pull a larger load at a
lower speed than it could by direct drive.

Only two types of transmissions are now extensively used, the
selective sliding and the planetary type. The progressive sliding
type and the friction drive are practially out of date.

Fig. 218 illustrates the selective sliding gear transmission
system. The desired gear ratio can be obtained by means of

AUTOMOBILES, TRUCKS AND TRACTORS 281

this type of transmission without shifting through other posi-
tions. This system is most generally used.

In Fig. 218, A is the driving shaft, B the driven shaft. $ and
L are slides carrying yokes that move on the wheels D and K.
All the wheels on the counter shaft are fast to the shaft. A lever
is arranged for shifting either S or L and for allowing the various
gears on the shaft B to mesh with those on the counter shaft.
This system is usually arranged for three speeds forward and one
speed reverse, but can be modified for any number of speeds for-
ward and for reversing. For reversing an idler gear is provided
between the driver and driven gears. High speed forward is

XZt <zs

Fig. 218. — The selective sliding-gear transmission system.

usually direct drive. Some cars have transmissions which per-
mit of a higher speed than the direct drive.

In the planetary transmission system, speed changes do not
depend upon the shifting of gears, but clutches or brakes are
applied to hold certain wheels in position. The drive is positive
and the gears are always in mesh. For high speeds this system
is very well adapted, as the entire system is clamped solidly and
revolves with the motor crank shaft as a single mass. As no
gears are turning idly the entire system by its weight serves to
steady the rotation of the motor at high speeds. The planetary
system provides only two speeds forward and one reverse. It is
inefficient in low speed and reverse, as much power is absorbed

282 STEAM AND GAS POWER ENGINEERING

by friction in the gears and clutches. The use of the planetary
system is limited to small automobiles.

Differentials for Automobiles.— Differential gears, sometimes
called compensating gears, are provided to permit one wheel

Fig. 219. — Bevel-gear differential.

to turn faster than the other on turning corners or when meeting
obstructions. The outside wheel in turning a corner has the
greater distance to travel than has the inside wheel in the same
length of time. In automobiles the differential is a part of the
rear axle assembly. If two drive wheels were rigidly connected

AUTOMOBILES, TRUCKS AND TRACTORS 283

without a differential it would be necessary for one wheel to
skid or slip when turning a corner or when going over an obstruc-
tion, thereby throwing great strain on the parts and producing
excessive wear on the tires.

The bevel gear differential (Fig. 219) is usually used on auto-
mobiles. The rear axle S (Fig. 219) is divided into two halves.
Each half of the rear axle carries a drive wheel at its outer end
and a bevel gear (C or Z>) at its inner end. The bevel gears C
and D are connected by, from two to four, differential or compen-
sating pinions (B, B, B) which are placed at equal distances apart
around the circle. These bevel pinions (B, B, B) are capable of
rotating loosely on radial studs, which are fastened at their outer
ends to the casing or housing 0. The gear A is made to turn
loosely upon the hubs of the bevel gear C and D, but is made fast
to the housing 0 by means of bolts or rivets. The power from the
engine is transmitted to the housing 0 through the bevel gear
pinion P which meshes with gear A. The housing transmits this
power through the small bevel pinions (B, B, B) to the bevel gears
C and Z>, which are connected to the rear or drive wheels. On a
level road with both drive wheels rotating at the same speed, the
housing 0, with all the gears and pinions will revolve as one mass,
and the small pinions (B, B, B) will remain stationary. The wheel
which turns the more easily is always the one to turn. In turning
a corner, in meeting an obstruction, in case one of the wheels
slips, or if the drive wheel attached to the bevel gear C must turn
slower than that attached to gear D, the differential pinions (B, B,
B) will revolve on their axes. The bevel pinions (B, B, B) divide
the torque between the two bevel gears C, D, thereby permitting
the two drive wheels to run at different speeds.

Universal Joint. — Since the engine and the gearing are mounted
on the frame of the automobile, while the driving wheels are
connected to the frame by springs, automobiles must be provided
with one or more flexible joints. The flexible joint is known as a
universal joint and consists of two forked arms at the ends of
shafts. These forked arms are joined by pins through their ends
to a center member and are arranged so that the pin of one forked
arm lies in the same plane, but at right angles to the pin of the
other. This permits the lower end of the propeller shaft to move
independently of the motion of the rear axle.

284 STEAM AND GAS POWER ENGINEERING

Front and Rear Axles. — The front axles are of a construction
which permits the wheels to pivot near the hub. This reduces
the tendency of the wheel to swing when striking an obstruction
in the road. The steering knuckles are the part of the front axle
assembly on which the wheels revolve. Steering arms are inserted
in the knuckles and are connected together with an adjustable
tie rod so that both knuckles turn simultaneously. A third arm,
usually on the left hand knuckle, is connected to the steering
gear by means of the steering connecting rod. Automobile
front axles are drop forged with I-beam cross sections.

Rear axles for automobiles are live axles; that is, they turn with
the wheels. They are divided into 3 types : the semi-floating, the
three-quarter floating, and the full-floating. In the semi-floating
type the entire load is carried on the axle. The bearing in a three-
quarter floating is on the housing and the wheel is keyed to the
axle; with this type it is not possible to remove the axle without
also removing the wheel. When a full-floating axle is used the
bearing is also on the axle housing and the entire weight is sup-
ported on the housing. With the full-floating type of rear axle
the only strain on the axle is the torque in turning the wheel ; as
the axle is not fastened rigidly at either end it can be taken out
without disturbing the wheel, by removing the hub flange.

Steering and Control Systems. — Automobiles are steered by
means of a hand wheel which is located on top of the steering
column. The steering gear operates on the front axle, through
the steering connecting rod, and turns the knuckles and the
front wheels. The steering column, besides the steering mechan-
ism, usually contains several concentric tubes with connections to
the alarm, the throttle control, and the spark control.

The spark and the carburetor throttle control levers are
usually located on top of the steering wheel. On some cars they
are located below the steering wheel.

Most modern cars are provided with two methods of throttle
control, the hand throttle control on the steering column and a
foot control, known as the accelerator.

The foot accelerator and the hand throttle control are so con-
nected that the hand accelerator also works the foot accelerator,
but the operation of the foot accelerator does not change the
position of the hand control.

AUTOMOBILES, TRUCKS AND TRACTORS 285

The control system includes a pedal for operating the friction
clutch, one for operating the service brake, a lever for operating
the emergency brake, and a lever for operating the speed changing
and reversing gears of the transmission. In some makes of cars
the service brake is operated by the clutch pedal and the emer-
gency by the other foot pedal.

The Ford automobile is controlled by three foot pedals and by
one hand lever. The pedals operate the clutch, the reverse, and
the service brake. The hand lever operates the clutch and the
emergency brake.

Brakes. — Automobile tires being made of rubber, the brakes
are not applied to the wheel tires, but to metal drums which are
fastened to the rear wheels. Two brakes are employed. One
brake called the service brake, is operated by means of a foot pedal.
The other brake, called the emergency brake, is usually operated
by a hand lever and is intended for use only in case the service
brake fails or in case a very strong braking action is required.
The braking effect can be produced by expanding the brake band
or shoe within the brake drum or by contracting the brake shoe
around the outside of the brake drum. Automobiles usually
have an external contracting brake for service, and an internal
expanding brake for the emergency brake.

The brake bands are usually covered on the rubbing side with
an asbestos preparation, which can be replaced when worn out.

Wheels and Tires. — Automobile wheels may be made of wood
or of metal. On most cars the wooden wheels go with the stand-
ard equipment. Wire wheels are light in weight, but require care
to keep all the spokes tight.

Automobiles use double pneumatic tires. The double pneu-
matic automobile tire consists of a rubber inner tube to be in-
flated and a casing, made up of rubber and canvas fabric, to
protect the inner tube from wear. Two types of casings are
used. They are known as the straight side and the clincher,
depending upon the method of holding the casing in the rim.

Carburetors. — Automobile carburetors have been illustrated
and described in Chapter XIII.

Ignition. — The jump spark electric ignition system is employed.
Most modern automobiles employ a high-tension distributor
system of ignition, using batteries as the source of current. Fig.

286 STEAM AND GAS POWER ENGINEERING

220 illustrates the wiring diagram of the Atwater Kent high-
tension distributor system, which is operated with a storage
battery, and includes the following:

1. A non-vibrator type of induction coil with primary winding,
secondary winding, and electric condenser. This type of induc-
tion coil produces only a single spark as the circuit is made and
broken only once. It is known as a unisparker.

2. A timer or contact-maker in the primary circuit. The
timer is constructed so that the length of contact is independent
of the engine speed.

3. A high-tension distributor with as many contact points
as there are cylinders.

DISTRIBUTOR

1 — MAArllito"

GROUND

CONTACT MAKER

Fig. 220. — Wiring diagram of the Atwater Kent system.

4. A governor which automatically advances the spark
within certain limits as the speed increases.

The automatic spark-advance mechanism, the contact maker,
and the distributor are all carried on one vertical shaft. The
point of ignition can also be hand-controlled by turning a sleeve
beneath the timer.

The Atwater Kent system works on the open circuit principle
and there is no danger of running down the batteries by leaving
a switch closed.

Fig. 221 illustrates the Delco system. This system includes
starting, generating, ignition, and lighting systems, all com-
bined in one. A motor-generator set performs the function of
cranking the engine and of supplying electrical current for igni-

AUTOMOBILES, TRUCKS AND TRACTORS 287

tion, lighting, sounding the horn, and charging the storage battery.
The motor-generator consists of a dynamo with two field windings,
and two windings on the armature with the commutators and
corresponding sets of brushes. This construction is made in

order that the machine may work both as a starting motor and
as a generator. The ignition apparatus is incorporated in the
forward end of the motor-generator. A combination switch is
used for the purpose of controlling the lights, the ignition, and
the circuit between the electrical generator and the storage
battery.

288 STEAM AND GAS POWER ENGINEERING

For ignition the Delco system employs a non-vibrator type of
induction coil with a timer in the primary circuit, and a distribu-
tor. A governor for automatic spark advance similar to that
of the At water Kent, but of different design is employed. In
Fig. 221, if button B is pulled out, the current for ignition will
be supplied by the dry cells. By pulling button M, current will be
supplied through wire A, if the generator is in operation, or by
the storage battery through wire B.

Automobile Starting Systems. — Automobile motors are started
by hand cranking or by some automatic starting device. Before
the motor is cranked the carburetor throttle lever on the steering
wheel should be moved to a position where the throttle is open.
The spark should be shifted to the retard position, as failure to
do this may result in the engine kicking back on account of
back firing. The gears should be placed into neutral position.

In cranking by hand, the crank should be pushed in
as far as possible and turned in the clockwise direction
until it catches. The motor should start if the crank is given a
quarter or a half turn in the right direction. In cranking an
engine, always set the crank so as to pull up. One should not
bear down on the crank.

Electric starting devices are usually employed in modern
automobiles. An electric self-starter consists of an electric
generator for furnishing electricity, a storage battery, and an
electric motor to crank the engine. The electric starting system
is also supplied with switches for the purpose of controlling the
supply of current; with protective devices such as fuses or cir-
cuit-breakers to prevent the discharging of the storage battery or
damage to the coils, motor, or lamps; with an electric regulator
to maintain constant voltage for the various speeds of the engine ;
and with electric meters for the purpose of showing the amount
of current supplied by the generator to the storage battery and
for indicating how much current is being supplied by the battery
for ignition and lighting.

Electric starters are built in the single-unit, the two-unit, or
the three-unit system. In the single-unit system the generator
and motor are in one unit and this motor-generator is used for
cranking the engine, for charging the storage battery, and for

AUTOMOBILES, TRUCKS AND TRACTORS 289

furnishing current to be used for operating the engine ignition
system and for the automobile lights. In the two-unit system
a separate motor, which receives its current supply from the
storage battery, is used for cranking the engine. The electric
generator supplies current for charging the storage battery and
also for ignition and lighting. In the three-unit system a magneto
furnishes current for the engine ignition system; a separate direct-
current motor, supplied with current from a storage battery, is
used for cranking; while the electric generator is used only for
charging the storage battery and for operating the lights.

Mechanical starters are also used to a limited extent on
small cars, but have been largely superseded by electric
starters. Some mechanical starters utilize springs, which
when released revolve the engine crankshaft. Other mechani-
cal starters depend for their action upon a clamp, but are
mainly hand-cranking devices with the driver remaining in the
seat. Safety cranks are also manufactured for the purpose of
reducing the danger of an accident in starting.

Automobile Lighting. — Electric lights are used almost exclu-
sively on modern automobiles. The electricity for illumination
is usually secured from a storage battery. In the cars with
electric starters, the storage battery is recharged from the gen-
erator; in other cases the battery is recharged from an outside
source. In some automobiles, notably the Ford, alternating-
current magnetos furnish lighting current while the car is in
motion.

A car lighted with a battery charged from an outside source is
equipped with a storage battery of 80 to 100 ampere-hour capac-
ity which supplies current for illumination and for blowing
the horn. This lighting storage battery is usually not used for
engine ignition, unless the car is equipped with a dynamo to re-
charge the battery. When the storage battery is used for light-
ing, ignition, and starting, its capacity should be at least 90
ampere-hours.

Management of Automobiles. — Before an attempt is made to
start an automobile the operator should be certain that the fuel
tank has sufficient gasoline, that the gasoline valve from the tank
to the carburetor is open, that the lubricating system is in good
working order, that the radiator is filled with clean water, and

290 STEAM AND GAS POWER ENGINEERING

that the engine ignition system is working properly. The trans-
mission system should be thrown into neutral position, the spark
lever should be shifted to the retarded position, and the carbu-
retor throttle should be partly opened before the engine is cranked.
The rules given in the discussion of starting systems should be
followed in starting an automobile by hand cranking. With
electric self-starters, the starting pedal is pushed forward or
down as far as it will go and held until the engine starts. As soon
as the engine starts the foot should be removed from the starter
pedal.

Easy starting may be obtained by throttling the air just as
the engine stops, thus leaving a rich mixture in the cylinders.
In extremely cold weather, or after prolonged standing of the
car, it may be necessary to prime the carburetor or even to
inject gasoline into the cylinder through each of the priming cups.

When the engine starts, the spark lever should be advanced.
To start the car, the emergency brake is released, the clutch is
disengaged, while the transmission gears are thrown into low
gear forward, and the foot accelerator and the spark lever are
operated to take care of the increased load on the car. In chang-
ing from low to intermediate and to high speed, the clutch is
thrown out, the gears are shifted, the clutch is thrown in mesh,
and the throttle, or foot accelerator, is adjusted for proper
operation.

To stop an automobile, the motor is slowed down by removing
the foot from the accelerator, the clutch is disengaged, the serv-
ice brake is operated so that the car comes to a gradual stop,
and the transmission gears are shifted into neutral position.

To stop quickly the operator presses on both pedals, releasing
the clutch and applying the service brake, while applying also
the hand emergency brake.

To reverse, the car is stopped, the reverse gear is shifted, and the
clutch is thrown in slowly.

Details concerning the care of a car are given in manufacturers'
instruction books and will not be repeated here.

An automobile engine will smoke if too much lubricating oil
is used, if the lubricating oil is of poor quality, if the piston rings
are worn or broken, or if the mixture of air and fuel is incorrect.

Engine hissing may be produced by loose or broken spark

AUTOMOBILES, TRUCKS AND TRACTORS 291

plugs, by leaving priming or relief cocks open, by having exhaust
pipe loosely connected, or by leaky gaskets or intake manifolds.

Irregular action of the automobile engine may be due to incor-
rect fuel mixture, poor wiring such as defective insulation or
defective connections, carbon deposits, poor fuel, or defects in
carburetor, magnetos, spark plugs, or mechanism.

Misfiring is often due to carbon deposits on the spark plug.
Overheating of the engine may be due to incorrect valve or spark
timing, defective water circulation, clogged radiator, or a lack of
proper lubrication Engine knocks are due to rich mixture, too
much spark advance, carbon deposits in the cylinder, loose or
worn bearings, loose flywheel, or lack of lubrication.

Trucks

Most of the essential parts of a truck are similar to those of an
automobile, but are usually heavier to stand the greater strains
imposed by the conditions under which a truck operates.

Power Plants for Trucks. — The truck power plant is usually a
four-cylinder vertical poppet valve type of internal-combustion
engine, which operates on the Otto four-stroke cycle. Six-cylin-
der engines are employed to a limited extent in trucks.

A standard type of float-feed carburetor is used, such as the
Stromberg plain tube or the Zenith. Some trucks are equipped
with special carburetors, such as the White, the Packard, or the
Pierce Arrow.

Truck motors are cooled with the forced water circulation sys-
tem and are usually provided with tubular radiators, in which
the upper and lower tanks are connected by a series of tubes
through which the water passes. Some of the lighter trucks
are equipped with cellular radiators similar to those used on
automobiles.

The jump spark system of ignition is employed. In some
makes of trucks, batteries are used for furnishing current when
starting and magnetos supply electricity for ignition after the
motor has attained normal speed. This is called the dual sys-
tem. Most trucks are equipped with a high-tension magneto.
In some cases trucks are provided with two independent ignition
systems, including a high-tension magneto and a distributor.

292 STEAM AND GAS POWER ENGINEERING

Power Transmission Systems for Trucks. — The power trans-
mission systems of trucks and of automobiles include the same
elements.

Some trucks employ a dry multiple disc clutch and others use
a wet multiple disc clutch. Dry or wet single-plate clutches are
also used for trucks. The principle of operation of the plate
clutch is similar to that of the cone clutch. The friction plate is
independent of the flywheel and of the housing and a spring
holds the friction surfaces in contact. The friction surfaces are
separated by depressing a foot pedal.

AjAftljj

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Fig. 222. — Truck transmission.

The transmission of a truck is usually of the selective type and
includes three speeds forward and one reverse. Some trucks em-
ploy a four-speed transmission system. Such trucks have direct
drive on the fourth speed and three lower gear ratios. To reduce
the danger of stripping gear teeth the gears of the counter shaft
and main shaft of the transmissions for heavy trucks are placed
permanently in mesh, the drive being obtained by the use of
shifting forks or clutches. A typical transmission for a heavy
truck is shown in Fig. 222.

The propeller shaft carries the power from the transmission
through the universal joints to the rear axles. The power from

AUTOMOBILES, TRUCKS AND TRACTORS 293

the propeller shaft to the rear axle is transmitted either by shaft
or by chain drive.

The shaft drive is the most common for trucks as well as for
automobiles. The shaft drive transmits the power to the differen-
tial, which is placed on the rear axle through bevel, helical, or
worm gears. The bevel gear drive is seldom employed for trucks.
The helical or spiral bevel gear drive is more satisfactory, as two
or more teeth are in mesh at one time, reducing irregularity
in wear. The worm gear drive is particularly well suited for
trucks, on account of the large gear reduction which this drive
makes possible. A large differential gear reduction decreases
the torque required to drive the rear wheels.

For heavy trucks chains are often used for the final drive in
order to obtain the greatest possible speed reduction. In such
trucks the differential is not placed on the rear axle, but is con-
tained in the same housing with the transmission. From the
differential the power is transmitted to jack shafts, which drive
the rear wheels by means of chains.

Some trucks are constructed so that they drive and steer with
four wheels. In such cases the power from the transmission is
transmitted to two differentials. One differential serves to trans-
mit the power to the front wheels and the other to the rear wheels.

The differential of the truck has the same function as that of
the automobile and permits the drive- wheels to revolve at differ-
ent speeds without interfering with the operation of the truck.

Tractors

Essential Parts of a Tractor. — A tractor consists of the fol-
lowing essential parts:

1. Power Plant. — This in the case of a steam tractor includes
a steam engine, a boiler, a pump or injector, steam and feed
water piping, fuel hopper, water storage, and the ordinary steam
power plant accessories. Gas tractors employ an internal com-
bustion motor burning gasoline, kerosene, or some heavier oil.

2. Speed Redaction Gears. — A train of gears must be interposed
between the motor and the drive wheels in order that the tractor
may be propelled at a very low speed.

J 3. Reversing Mechanism. — A steam tractor is reversed by a
Stephenson link motion similar to that used for reversing loco-

294 STEAM AND GAS POWER ENGINEERING

motives or by some form of single eccentric radial valve gear.
Gas tractors employ a train of gears.

4. Steering Mechanism. — -Steering is usually accomplished by
turning the front axle.

5. Friction Clutch. — A friction clutch is necessary for the pur-
pose of disengaging the motor from the propelling gear. The
expanding cone and the expanding shoe clutches are used in
addition to those explained. Fig. 223 illustrates an expanding
shoe clutch.

Fig. 223.— Tractor clutch.

6. Differential.— The differential (Fig. 224) is similar to that
used on trucks and its function is to allow one drive wheel to
revolve independently of the other.

7. Tractor Frame. — The frame supports the various parts and
keeps them in proper alignment.

8. Drive Wheels and Steering Wheels. — Usually the two rear
wheels are the drive wheels and the two front wheels are used
for steering. Some tractors employ a drum for driving, several
makes are constructed so that the front wheels are the driving
wheels, and in other makes all four wheels drive. Tractors
are also built on the " Caterpillar" principle and employ a crawler
instead of a wheel or drum.

AUTOMOBILES, TRUCKS AND TRACTORS 295

Steam Tractors. — The steam tractor, or traction engine, is
usually equipped with an internally fired boiler. Some builders
use the return flue type, others the direct flue or locomotive type.

Coal, lignite, wood, straw, or crude oil are used as fuels for
steam tractors.

The feed water is delivered to the boiler by an injector, a direct-
acting steam pump, a cross-head pump, or a gear-driven pump.
Some tractors employ two independent methods for feeding water
to the boiler.

■T 4

1 5 B

^ S ^ A.J

^^^^v^l

Fig. 224. — Tractor differential.

Feed-water heaters are used in connection with the better types
of steam traction engines.

A simple type of slide valve engine is employed. Some tractors
are provided with double-cylinder engines. Compound engines
are also used to some extent.

Gas Tractors. — The use of the gas tractor has been increasing
much more rapidly than that of the steam tractor. Gas tractors
are made in many different sizes, prices, and special designs
suitable for various uses. A gas tractor can be started much more
quickly than one propelled by a steam engine and requires less
attention.

296 STEAM AND GAS POWER ENGINEERING

The motors of gas traction engines usually operate on the Otto
four-stroke cycle and use gasoline or kerosene for fuel. The
motors are either vertical or horizontal and operate at moderate
speeds as compared with the motors used on automobiles. The
vertical motor resembles the truck motor, but is usually heavier.
Fig. 225 illustrates the type of motor commonly used on gas
tractors.

Float-feed carburetors of the single jet automobile type are
generally used.

Fig. 225. — Four-cylinder tractor motor

Nearly all tractors employ the jump-spark ignition system.
The ignition system differs from that of automobiles in that
magnetos are commonly employed.

Rating of Tractors. — Two ratings are usually given to tractors.
One is in brake or belt horsepower. This indicates the power
developed at the shaft of the engine, which can be used for driv-
ing various machines by means of belt drive. The other rating
is the tractive or draw-bar horsepower. The tractive horse-
power is usually one-half to two-thirds of the brake horsepower,

AUTOMOBILES, TRUCKS AND TRACTORS 297

depending upon the transmission gearing and on the character
of the ground over which the tractor must be propelled.

Care of Trucks and Tractors. — The general directions given
concerning the care of an automobile apply to the truck and
tractor. Wearing surfaces must be kept well lubricated and lost
motion in bearings must be avoided.

The steering mechanism of the tractor is less sensitive than
that of the automobile or even of the truck on account of its
slower speed and the lower gear ratio of the steering wheel.

Overloading a truck or a tractor is a serious mistake. The life
and usefulness of any piece of machinery is increased by proper
housing and systematic upkeep. The lubricating system of the
motor should be examined daily. Frequent inspection should
be made to determine the condition of the spark plugs, the align-
ment of the wheels, condition of the brakes, clutch, springs, rods,
cylinders, and bearings. Valves should seat properly and should
be correctly timed.

Problems

1. Make clear sketches showing the mechanism of an automobile steering
gear.

2. Make a clear sketch of a universal joint.

3. Prepare a table showing the important differences in the specifications
of automobiles and of trucks.

INDEX

Air brakes, 270

Air-cooled gas engine, 201

Air pump, dry, 174

Air pump, wet, 173

Air required for combustion, 18

Acohol, denatured, 218

Alcohol fuel, 217

Angle valve, 88

Anthracite coal, 14

Ash handling machinery, 81

Automobile axles, 284

brakes, 285

clutch, 279

control system, 284

cooling systems, 275

differential, 282

electric, 273

gasoline, 273

ignition systems, 285

lighting, 289

lubrication, 276

management, 289

motors, 274

parts, 274

starting systems, 288

steam, 273

steering system, 284

tires, 285

transmissions, 280

types, 273

valves, 278

wheels, 285
Axles, automobile, 284

Babcock & Wilcox boiler, 45
Balanced valves, 98
Batteries, electric, 241

primary, 242

storage, 242

Bearings, 127
Benzol, 218
Blast furnace gas, 219
Blow-off valve, 88
Bituminous coal, 15
Boiler, capacity of, 53

classification of, 35

efficiency of, 53

management, 56
Boiler furnaces, 52
Boiler, heating surface, 51

horizontal tubular, 36

locomotive, 39

marine, 39

marine water tube, 49

plain cylindrical, 35

settings, 52

staying, 51

vertical fire tube, 41

water tube, 43
Boiler with dome, 37
Brake horse power, 122, 256
Branca turbine, 138

Calorimeter, coal, 11

gas, 212
Capacity of boilers. 53
Carburetion, principles of, 228
Carburetors, float feed, 229

Holley, 235

kerosene, 236

Kingston, 230

Marvel, 231

Stewart, 232

Stromberg, 233

Zenith, 235
Check valve, 88
Chemistry of combustion, 17
Chimneys, 72

capacity of, 73

draft, 72
299

300

INDEX

Clutch, automobile, 279

cone, 279

disc, 279
Clutch, truck, 292
Coal, anthracite, 16
Coal as fuel, 13, 14, 15
Coal, bituminous, 15
Coal calorimeter, 11
Coal handling machinery, 81
Coke-oven gas, 219
Combustion, 17

Compound impulse turbines, 143
Compound steam engine, 107
Compression pressures for various
internal combustion engine
fuels, 195
Condenser, barometric, 168

ejector, 170

jet, 167

principle of, 164

surface, 171

types, 166
Conveyors for coal and ashes, 81
Cooling ponds, 177
Cooling towers, 177
Crank shaft, 92

Cross compound steam engine, 109
Crude oil, 217

Crude petroleum distillates, 214
Curtis steam turbine, 150

Dead center, 92

DeLaval simple impulse turbine, 138

Diesel internal combustion engine,

198
Differentials for automobiles, 282
Distillates of petroleum, 214
Distributor system, 250
Draft, artificial, 74

forced, 74

gages, 185

induced, 75

natural, 72
Dynamo, ignition, 246
Dynamometers, 189

Eccentric, 93

Economizer, 70

Economy of steam engines, 129

Economy of steam turbines, 161

Edison storage battery, 245

Efficiency, mechanical, 123

Efficiency of boilers, 53

Electric batteries, 241

Energy of steam, 142

Energy, source of, 2

Engine. See Steam engine or Internal

combustion engine.
Engine condensing, 106
Engine, Corliss, 100

non-condensing, 107

reversing, 102
Erecting pipe, 86
Exhaust head, 181
Exhaust steam turbines, 160
Expansion joints, 86
Expansion of piping, 85

Feed pumps, 76
Feed water heater, 68

closed type, 70

open type, 69
Feed water heating, economy of, 68
Fire tube boiler settings, 36, 37,

38
Firing, 55
Fittings, flanged, 83

screwed, 38
Flue gas analysis, 19
Flywheel, 93
Four stroke cycle, 192
Friction horsepower, 123
Fuel, flash point of, 214
Fuel gases, 218
Fuel, selection of, 213
Fuel, specific gravity of, 213
Fuels for internal combustion en-
gines, 211
Fuels for steam power, 10

INDEX

301

Fuels, heating value of, 10, 212

liquid, 211

proximate analysis, 12
Furnaces for boilers, 52
Fusible plug, 91

History of the steam turbine, 137
Hit-and-miss governing, 252
Horizontal tubular boiler, 36
Horse power, definition of, 114
Horse power, indicated, 114
Hot air engine, 3, 4

Gage, steam, 89
Gas calorimeter, 212
Gas engine. See Internal combus-
tion engine.
Gas engine governor, 251
Gas engine indicator diagram, 195
Gas engine, starting of, 207
Gasoline, 216
Gasoline, casing head, 216

cracked, 216

straight refinery, 216
Gas producers, 220

classification of, 222

combination, 223

details of, 220

down draft, 224

operation, 226

pressure, 223

rating of, 226

suction, 222

testing, 258
Gate valve, 87
Globe valve, 87

Governors for gas engines, 252
Governors for steam engines, 124,

125, 126
Grates for furnaces, 80
Grate, shaking type, 81

Heat consumption of gas engine, 256
Heating surface of boilers, 51
Heating value of fuels, 10
Heine boiler, 45
Hero's turbine, 137
History of internal combustion en-
gine, 191
History of the steam engine, 94

Igniter, hammer brake, 238
Igniter, wipe-spark, 238
Ignition, Atwater Kent, 286
Ignition, Delco, 286
Ignition dynamo, 246
Ignition, electric, 237

hot tube, 236

jump spark, 239

make-and-break, 237
Ignition systems, 236
Indicated horse power of gas engines,

256
Indicator card, 118
Indicator for steam engines, 155
Indicator reducing motions, 117
Indicator reducing wheel, 118
Inductance coil, 237
Induction coil, 239
Injectors, 79
Installation of internal combustion

engines, 206
Installation of steam engines, 130
Installation of steam turbines, 161
Internal combustion engine, 191

care of, 207, 208, 209

compression pressures, 195

details, 200

history, 191

losses, 206

operation, 207, 208, 209

parts, 193

timing, 208, 209

Kerosene, 217
Kerr steam turbine,

147

302

INDEX

Lead of a valve, 97
Lead storage battery, 244
Lenoir engine, 192
Lignite, 15

Locomobile, steam, 109
Locomotive boiler, 39

classification, 274

compound, 266

details, 260

development, 266

history of, 264
Locomotive stoker, 268
Locomotive superheater, 267
Losses in steam engines, 95
Lubrication, automobile, 276
Lubricators for steam engines, 128,
129

Magneto, 246

high tension, 248

inductor type, 247

low tension, 247
Management of boilers, 56
Marine boiler, 39
Marine water tube boiler, 49
Materials for boilers, 50
Mechanical efficiency, 123
Mixer valves, 228
Motor, definition of, 1
Motor, electric, 3
Muffler, 254

Natural gas, 219
Newcomer engine, 95

Oil, crude, 217

Oil engines, 204

Oil engine, semi- Diesel type, 205

Oil fuel for steam making, 16

Orsat apparatus, 19

Otto cycle, 192

Parker boiler, 48

Parsons steam turbine, 155

Parts of a steam engine, 92, 93, 94

Petroleum distillates, 214

Pipe bushing, 85

Pipe cap, 85

Pipe couplings, 84

Pipe covering, 86

Pipe, cross, 85

Pipe, erecting, 85

Pipe, double extra heavy, 83

elbow, 85

extra heavy, 83
Pipe fittings, 83, 84, 85
Pipe flange, 85
Pipe sizes, 83
Pipe, standard, 83
Pipe tee, 85
Pipe unions, 84
Piping grades, 83
Planimeter, 120
Plain slide valve, 96
Plain slide valve types, 98
Plug, fusible, 91

Power, amount used for manufac-
turing, 5
Power, development of, 1
Power from indicator cards, 119
Power, measurement of, 189
Preignition, 209
Primary batteries, 242
Producer gas, 219
Producers, gas, 220
Prony brake, 123
Pump, circulating, 175
Pump, direct acting, 77
Pumps, duty of, 80

vacuum, 171
Pyrometers, 186

Radial valve gears, 106
Radiation loss, 96
Rateau turbine, 143

INDEX

303

Reaction turbine, 154
Reversing steam engine, 102

Safety valve, 88

lever, 88

pop, 89
Separating calorimeter, 32
Separator, oil, 180
Separators, steam, 179
Settings for boilers, 52
Shale oil, 218
Solar motor, 3, 4
Spark plug, 240
Speed measurement, 189
Spiro turbine, 159
Spray ponds, 177
Steam calorimeters, 31, 32
Steam chest, 92
Steam, energy of, 142
Steam engine, 92

care of, 130

compound, 107

connecting rod, 127

cross head, 127

Corliss, 100

details, 126, 127

economy, 129

governor, 124, 125, 126

history, 94

indicator, 115

installation, 130, 131

losses, 95

operation, 131, 132, 133, 134

parts, 92, 93, 94

piston, 126

Uniflow, 102
Steam gage, 89
Steam generation, 21
Steam locomobile, 109
Steam meters, 187
Steam power plants, 5, 6, 7, 8
Steam power plant testing, 182
Steam, quality of, 22, 30
Steam separators, 179
Steam tables, 23-28

Steam trap, 90

Steam, velocity of, 142

Steam turbines, 135

Steam turbine, Westinghouse, 150,

158
Steam turbine, double-flow, 158

advantages of, 136

applications, 160

blading, 152, 158

care of, 161

Curtis, 150

DeLaval, 138, 148

economy, 161

exhaust types, 160

governors, 140, 154, 156

history of, 137

impulse-reaction type, 158

Kerr, 147

nozzles, 140, 151

Parsons, 155

Rateau, 143

Reaction type, 154

Spiro, 159

Sturtevant, 150

Terry, 149

Westinghouse, 150, 158
Steam, velocity of, 142
Stephenson link motion, 105
Stirling boiler, 45
Stoker, American underfeed, 68

Chain grate, 63

classification, 63

economics of, 63

field for, 62

inclined grate, 64

Jones underfeed, 66

Murphy, 65

Roney, 65

Westinghouse, 68

underfeed, 66
Storage batteries, 242
Storage battery, lead type, 244

Edison, 245
Sun, source of energy, 2
Superheater, attached type, 58

Babcock & Wilcox, 60

Foster, 62

304

INDEX

Superheater, Heine, 61

independently fired, 58
overheating, 59
Stirling, 60
types, 58

Tandem compound steam engine,

108
Terry steam turbine, 149
Throttling calorimeter, 31
Timer, 249
Tractor, care of, 296
Tractor details, 293
Tractor motors, 295
Tractors, gas, 295

rating, 296

steam, 295
Transmission, automobile, 280

planetary, 281

selective, 281
Trap, steam, 90
Truck, care of, 296

details of, 291

motor, 291

power plant, 291

power transmission, 292
Turbine. See Steam turbine.
Two-stroke cycle, 196

Uniflow steam engine, 102
Union, pipe, 84
Unit of heat, 11
Universal joints, 283

Valve, poppet, 101, 278

sleeve type, 278
Vertical fire tube boiler, 41
Vacuum measurement, 165
Valve, safety, 88
Valves, 87

angle type, 88

balanced, 98

blow off, 88

Corliss, 100

double ported, 99

gate, 87
Valve gears, radial, 106
Valve, globe, 87

setting, 110, 111, 112, 113, 114

setting by indicator, 121
Valve timing of gas engines, 208
Velocity of steam, 142
Venturi meter, 185
Volatile matter in fuel, 12

Walschaert valve gear, 106

Water column, 90

Water cooled gas engine, 201

Water glass, 90

Water tube boiler, 43

Watt engine, 95

Weir, 184

Wickes boiler, 47

Windmill, 3, 4

Wood as fuel, 13

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