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ENGIN. 
LIBRAE ' 



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neumatie 
Conveying 




PHILLIPS 



PNEUMATIC CONVEYORS 




Engineering 
Library 



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ASHWELL&NESBIT,Ltd. 

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ALSO AT 
BIRMINGHAM, GLASGOW, MANCHESTER AND LIVERPOOL I 



1 SPECIALISTS IN PNEUMATIC 1 
1 CONVEYING PLANTS FOR ALL I 
1 :: :: MATERIALS :: : 

"NUVAKO" SYSTEM 



j| SCHEMES PREPARED AND COMPLETE 
| ESTIMATES GIVEN INCLUSIVE OF SKILLED 
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PITMAN'S TECHNICAL PRIMER SERIES 

Edited by R. E. NEALE, B.Sc., Hons. (Lond.) 
A.C.G.I., AM.I.E.E. 



PNEUMATIC CONVEYING 



PITMAN'S TECHNICAL PRIMERS 

Edited by R. E. NEALE, B.Sc. (Hons.), A.C.G.I., A.M.LE.E. 

IN each book of the series the fundamental principles of some 
sub-division of engineering technology are treated in a practical 
manner, providing the student with a handy survey of the particular 
branch of technology with which he is concerned. Each 2s. 6d. net. 

THE STEAM LOCOMOTIVE. By E. L. AHRONS, M.I.Mech.E. 
BELTS FOR POWER TRANSMISSION. By W. G. DUNKLEY. B.Sc. 
WATER-POWER ENGINEERING. By F. F. FERGUSSON, A.M.I.C.E. 
PHOTOGRAPHIC TECHNIQUE. By L. J. HIBBERT, F.R.P.S. 
HYDRO-ELECTRIC DEVELOPMENT. By J. W. MEARES, M.Inst.C.E. 
THE ELECTRD7ICATION OF RADLWAYS. By H. F. TREWMAN, M.A. 
CONTINUOUS CURRENT ARMATURE WINDING. By F. M. DENTON. 
MUNICIPAL ENGINEERING. By H. PERCY BOULNOIS, M.Inst.C.E. 
FOUNDRYWORK. By BEN SHAW and JAMES EDGAR. 
PATTERNMAKING. By BEN SHAW and JAMES EDGAR. 
THE ELECTRIC FURNACE. By FRANK J. MOFFETT, B.A., M.I.E.E. 
SMALL SINGLE-PHASE TRANSFORMERS. By E. T. PAINTON. B.Sc. 
PNEUMATIC CONVEYING. By E. G. PHILLIPS, M.I.E.E., A.M.I.Mech.E. 
BOILER INSPECTION AND MAINTENANCE. By R. CLAYTON. 
ELECTRICITY IN STEEL WORKS. By W. MACFARLANE, B.Sc. 
MODERN CENTRAL STATIONS. By C. W. MARSHALL, B.Sc. 
STEAM LOCOMOTIVE CONSTRUCTION AND MAINTENANCE. By 

E. L. AKRONS, M.I.Mech.E., M.I.Loco.E. 

HIGH TENSION SWITCHGEAR. By H. E. POOLS, B.Sc., A C.G.I. 
HIGH TENSION SWITCHBOARDS. By the Same Author 
POWER FACTOR CORRECTION. By A. E. CLAYTON, B.Sc., A.K.C 
TOOL AND MACHINE SETTING. By P. GATES. 
TIDAL POWER. By A. STRUBEN, O.B.E., A.M.I.C.E. 
SEWERS AND SEWERAGE. By H. G. WHYATT, M.Inst.C.E. M.R.S.I. 
ELEMENTS OF DLLUMINATING ENGINEERING. By A. P. TROTTER, 

M.Inst.C.E. 

COAL-CUTTING MACHINERY. By G. E. F. EAGAR, M.Inst.Min.E. 
GRINDING MACHINES AND THEIR USE. By T. R. SHAW, M.I.Mech.E. 
ELECTRO-DEPOSITION OF COPPER. By C. W. DENNY, A.M.I.E.E. 
DIRECTIVE WIRELESS TELEGRAPHY. By L. H. WALTER, M.A. 
TESTING OF CONTINUOUS-CURRENT MACHINES. By C. F. SMITH, 

D.Sc., M.I.E.E. 

ELECTRICAL TRANSMISSION OF ENERGY. By W. M. THORNTON, D.Sc. 
STEAM ENGINE VALVES AND VALVE GEAR. By E. L. AKRONS, 

M.I.Mech.E. 

MECHANICAL HANDLING OF GOODS. By C. H. WOODFIELD. 
INDUSTRIAL AND POWER ALCOHOL. By R. C. FARMER, D.Sc. 
POSITION AND DIRECTION FINDING. By L. H. WALTER, M.A., 

A.M.LE.E. 
HIGH-TENSION TRANSFORMERS. By W. T. TAYLOR, M.Inst. C.E. 

LONDON : SIR ISAAC PITMAN & SONS, LTD. 




Frontispiece 

INTAKE END OF PNEUMATIC CONVEYOR. 
Adjustable to follow rise and fall of vessel on tidal waters. 



PNEUMATIC 
CONVEYING 



A CONCISE TREATMENT OF THE 
PRINCIPLES, METHODS AND APPLICATIONS 
OF PNEUMATIC CONVEYANCE OF MATERIALS 

WITH SPECIAL REFERENCE TO THE CONVEYING 
AND ELEVATING OF HEAVY SOLID MATERIALS 



FOR ENGINEERS, WORKS MANAGERS, 
AND STUDENTS 



BY 



E. G. PHILLIPS 

M.I.E.E./U.M.I.MECH.E. 




LONDON 

SIR ISAAC PITMAN & SONS, LTD. 
PARKER STREET, KINGSWAY, W.C.2 

BATH, MELBOURNE, TORONTO, NEW YORK 
1921 



Engineering 
Library 



PRINTED BY 

SIR ISAAC PITMAN & SONS, LTD. 
J ENGLAND 

I 






PREFACE 

PNEUMATIC Conveying has recently attracted great 
and widespread interest amongst engineers and 
others interested in the economical handling of 
materials. The information hitherto available on 
the subject has, however, been so meagre and so 
indefinite that the author offers this concise 
treatment of principles, methods and applications 
in order that those who are anxious to avail them- 
selves of this flexible means of transportation may 
know just how, and why, it is worthy of their 
attention. 

The high cost of labour, coupled with the desire 
to improve the condition of the worker who has 
had to work in a dust laden atmosphere of an 
objectionable, or even poisonous nature, will create 
such a demand for pneumatic conveying plant 
that present day methods of transportation will 
be revolutionized in many branches of industry. 

The author has had three years' experience with 
one of the first pneumatic plants erected in this 
country, for use with coal, ashes, and flue dust, 
and he has conducted numerous experiments on 
other materials, such as sand, oxide, potatoes, 
various chemicals, etc., and has endeavoured to 
add his quota to the information available for the 
benefit of other engineers and works managers. 

Experiments proved that with certain materials 
vii 

466528 



V1U PREFACE 

the discharger was the weak link in the chain, 
as wet sticky materials entering at a high velocity 
" packed " tight and would not discharge freely. 
This led to experiments which, with the valuable 
assistance of Mr. H. B. Clarke, A.M.I. E.E., resulted 
in overcoming this difficulty by means which are 
described fully in Chapter VI. 

No attempt has been made to go fully into the 
questions of domestic vacuum cleaners, removing 
dust from manufacturing processes, etc. The 
chief aim has been rather to bring into prominence 
the flexibility and other advantages of moving 
air as a means of conveying and elevating heavy 
solid materials which hitherto it has been thought 
could not be handled in this manner. 

The author gladly acknowledges the interest 
and information given by the following firms and 
individuals Mr. H. B. Clarke, A.M.I.E.E. ; 
Messrs. Ashwell & Nesbit ; Boby, Ltd. ; H. J. H. 
King & Co., Ltd. ; The Lamson Store Service Co. ; 
and the Sturtevant Engineering Co., Ltd. 

E. G. PHILLIPS. 

NOTTINGHAM. 



CONTENTS 



CHAP. PAGE 

PREFACE ...... vii 

I. SYSTEMS AND APPLICATIONS OF PNEUMATIC 

CONVEYING ..... 1 

II. DETAILS OF PLANT PUMPS, EXHAUSTERS 

AND AIR FILTERS .... 10 

III. DETAILS OF PLANT (CONTD.) DIS- 

CHARGERS, PIPE LINES AND SUCTION 

NOZZLES ...... 28 

IV. TYPICAL INSTALLATIONS FOR GRAIN . 45 
V. PNEUMATIC COAL HANDLING PLANTS . 54 

VI. THE INDUCTION CONVEYOR ... 62 

VII. STEAM JET CONVEYORS ... 72 

VIII. MISCELLANEOUS APPLICATIONS OF PNEU- 
MATIC CONVEYING .... 80 

BIBLIOGRAPHY . . . . .105 

INDEX 107 



ILLUSTRATIONS 

FIG. PAGE 
Intake end of Pneumatic Conveyor, with 
rise and fall adjustment . Frontispiece 

1. King's pneumatic system. Steam-driven 

air pump . 

2. Sturtevant rotary blower . . .17 

3. Nash " Hydro-Turbo " exhauster . . 19 

4. Sturtevant " Cyclone " dust separator . 21 

5. Automatic bag filter .... 23 

6. Mollers' air filter 24 

7. Sturtevant wet filter .... 26 

8. Fixed discharger with glass receiver . 30 

9. Sturtevant patent junction ... 33 

10. Course taken by material round bend . 35 

11. Segment -back bend .... 35 

12. Lobster bend 35 

13. King full -way junction valve ... 37 

14. Suction nozzles for high pressure systems 40 

15. Sturtevant equipment removing wood 

refuse from double tenoning machine . 41 

16. Sturtevant equipment removing dust from 

sand papering machines ... 42 

17. 18. Ancient and Modern ... 46 
19. Typical gram -handling plant ... 47 



xii ILLUSTRATIONS 

FIG. PAGE 

20. Floating pneumatic transport plant . 49 

21. Portable pneumatic plant on railway truck 50 

22. Portable railway plant in operation . 52 

23. Pneumatic unloading of coal ... 55 

24. Discharger for coal conveying plant . 57 

25. Brady steam jet ash conveyor . . 75 

26. Typical Lamson inter-communication 

carrier ...... 82 

27. Tube central in wholesale drug house . 87 

28. Lamson distributing station . . .88 

29. Stationary turbo -exhauster with dust 

separator . . . . . .91 

30. Portable turbo -exhauster . . .91 

31. Suction cleaning for railway carriage 

cushions ...... 93 

32. Sturtevant equipment for office cleaning 93 

33. 34. Air lift pumping .... 93 



PNEUMATIC 
CONVEYING 



CHAPTER I 

SYSTEMS AND APPLICATIONS OF PNEUMATIC 
CONVEYING 

CONVEYING by mechanical means has existed for 
many centuries, and is one of the earliest forms of 
man's ingenuity towards labour saving as we know 
it to-day. The pneumatic conveyance of materials 
from one position to another, either horizontally 
or vertically, is the most recent form of automatic 
handling of solid substances. 

Genesis and Applications of Pneumatic Conveying. 
The need of water for human consumption and 
for irrigation purposes caused the ancient inventor 
to carry out nearly all his experiments with that 
substance, and the first instance we have of any- 
thing approaching pneumatic conveying is the 
well known injector in which steam is passed 
through one pipe, placed at right angles to a second 
pipe, at such a velocity as to reduce the pressure 
in the second pipe to below the atmospheric 
pressure. The excess of atmospheric pressure over 
1 



2 I' 

the reduced pressure in the second pipe then drives 
up the latter the material (in this case water) in 
which the end of the pipe is submerged. This 
invention is about a century old, if it emanated 
from the Marquis Mammonry d'Eclet, in 1818, 
as is usually believed. 

The first practical application of this invention 
to other than liquid materials is supposed to have 
been in connection with the conveying of cotton 
in a loose form, as an improvement upon the 
manual shifting of large bales. This develop- 
ment was made about 1867, and after this date 
great progress was made, principally in connection 
with the handling of grain, wheat, malt, etc., and 
largely owing to the work of an American named 
A. K. Williams. 

At the present day it is hardly possible to 
enumerate all the successful schemes for the pneu- 
matic handling of materials. In addition to 
installations for the conveyance of materials such 
as those mentioned above is the pneumatic tube, 
for conveying papers, messages and cash in offices 
and between shop counter and cash desk, etc. 
Also, there is the suction cleaner, ranging in appli- 
cation from the handling of refuse and dust from 
saw mills and woodworking machinery to the 
removal of fine abrasive and poisonous particles 
in certain manufacturing processes. Small suction 
cleaners are, of course, now quite familiar domestic 
appliances. The sand-blasting machine is really 
another example of a self contained pneumatic 
conveyor on a small scale. 



SYSTEMS OF PNEUMATIC CONVEYING 3 

Ashes, coal, oranges, sugar, chemicals, spent 
oxide, iron ore, spent tanning bark, and many 
other materials are now actually transported, 
elevated or conveyed pneumatically, and it must 
here be acknowledged that the first really successful 
plant in this country was due entirely to the 
initiative and inventive genius of Mr. Frederic 
Eliot Duckham, late Chief Engineer to the Milwall 
Dock Co., who in 1888 commenced experiments 
in grain handling by suction. In 1892 he produced 
a very successful floating plant for unloading ships 
into land silos, and this installation was the 
prototype of many similar plants which were placed 
in commission all over the world. Many improve- 
ments have been carried out and numerous patents 
issued for pneumatic handling apparatus, but the 
original scheme as designed by Mr. Duckham has 
never been departed from seriously. 

Fundamental Principles and Components. The 

pneumatic conveyance of materials along pipes is 
most easily understood when the equipment is 
considered as a pump producing a high velocity 
stream of air in which the material to be trans- 
ported is floating, and with which it is carried 
through the pipe system. It is necessary fully to 
understand this, as it is otherwise difficult to 
realize how it can be possible to lift solids at the 
rate of 100 tons or more per hour, several hundred 
feet up a pipe in which the vacuum does not 
exceed about 7 inches mercury column (say, 
11 Ib. per sq. in. absolute). 



4 PNEUMATIC CONVEYING 

A modern pneumatic conveying plant of the 
suction type comprises : (1) An exhauster, or an air 
pump, of either the reciprocating or the rotary 
type. (2) A suction nozzle. (3) A discharger, 
whereby the material is extracted from the pipe 
line at the desired position, without " breaking " 
or losing the vacuum. (4) One or more appliances 
for filtering the air and extracting any foreign 
material which may have been carried over from 
the discharger and which would damage the 
cylinder walls of the exhauster if allowed to enter 
the plant. 

It is necessary . here to mention that all pneu- 
matic conveying is not done by exhausting, but 
frequently by the use of pressure, that is, that the 
air is not sucked along the transport line but is 
actually blown in under pressure by fans, air 
compressors, or rotary blowers, according to the 
circumstances. 

The suction system is preferable when it is 
required to convey materials from several outlying 
points to one central storage bunker or area. On 
the other hand, the pressure system is less expensive 
in first cost, when it is required to transport from 
one central point to numerous outlying plants 
in the area to be served. A combination of the 
suction and pressure systems is now being de- 
veloped for the handling of materials in cases 
where neither the " suction " nor the " blowing " 
scheme alone can be said to be successful. This 
combined system is known as the induction system 
and is discussed in Chapter VI. 



SYSTEMS OF PNEUMATIC CONVEYING 5 

Advantages over Mechanical Conveyors. The 

reasons why pneumatic methods for elevating and 
conveying are now receiving such attention are to 
be found in the advantages of pneumatic over 
mechanical conveying. These may be summarized 
as follows : Economy in labour ; flexibility of 
plant both in design and operation ; elimination 
of dust and its harmful effects on the employees ; 
and in many instances the recovery of dust which 
is valuable and which would otherwise represent 
a serious financial loss. Wear and tear on moving 
parts is reduced to a minimum. All obstacles 
such as buildings, roads, rivers, railways, etc., can 
be overcome easily since the conveyor is " only a 
pipe." Should circumstances not permit of a 
straight single run for such appliances as bucket 
elevators, it is usually necessary to bag and cart 
the material from one position to another, but 
this is avoided by pneumatic elevating and con- 
veying, because the pipe can be carried up or down, 
round corners, over or under roads, etc. 

Hundreds of instances still exist in which loose 
material in barges is shovelled into bags, which 
are lifted by an ordinary friction hoist into a 
building over the quay -side. The sacks are wheeled 
by manual labour into the building, and emptied 
into hoppers or silos, the empty bags being lowered 
again for a further cycle of operations. This 
costly multiple handling may be obviated by the 
erection of a small pipe line which will auto- 
matically feed itself at one end, and discharge 
evenly and continuously into the receptacle 

2 (5362) 



6 PNEUMATIC CONVEYING 

provided. The whole of the " moving parts " 
may be situated in one position, which enables 
them to be carefully inspected, oiled and kept in 
repair, etc. 

Cranes, hoists, telphers, and belt conveyors all 
have their special spheres" of usefulness, but no 
other plant can claim all the advantages of the 
pneumatic system as outlined above. 

Pneumatic Conveying Systems. As mentioned 
above there are three main systems of pneumatic 
conveying, viz. 

(1) Conveying by air above atmospheric pressure. 

(2) Conveying by air below atmospheric pressure. 

(3) Conveying by air above and below atmos- 
pheric pressure, by a combination of (1) and (2), 
known as the induction system. 

Although these are the main headings under 
which the subject may be considered, they must 
be sub -divided further as follows 

(1) Conveying above Atmospheric Pressure, (a) 

Low pressure systems using single stage centrifugal 
fans, and suitable for conveying such materials as 
wool, cotton, bark, chopped straw, paper clippings, 
sawdust, shavings, jute, and fibrous materials of 
many kinds. 

(b) High- pressure systems using multi-stage fans 
and blowers of the rotary type or positive design, 
and suitable for conveying materials of a denser 
nature such as dry sand, sugar, etc., also for 
pneumatic despatch tubes. 



SYSTEMS OF PNEUMATIC CONVEYING 7 

(2) Air Suction Systems, (a) Large pipe systems 
using ordinary steel plate centrifugal fans, and 
applied to handling the waste products and 
injurious dust in many industries, such materials 
being sawdust and shavings from woodworking 
machinery ; emery dust from grinding wheels ; 
dust and lint from polishing mops ; leather dust 
from heel and sole scouring plants ; starch dust 
in confectionery works ; colour dust in works 
manufacturing pigments ; and bronze dust in 
printing works. Many other examples will no 
doubt occur to the reader. 

(b) Small pipe systems using multi-stage cen- 
trifugal fans or rotary blowers. Under this section 
the most important plants are undoubtedly those 
for domestic vacuum cleaning. Large stationary 
plants for this purpose are installed in many 
hotels, offices, buildings, workshops, theatres, large 
private houses, etc. 

(c) Heavy commercial systems in which the fan is 
replaced by a reciprocating exhauster, producing 
currents of air suitable for conveying such materials 
as coal, ashes, sugar, leather tanning bark, ores, 
granite chippings, wood blocks, oranges, etc., 
which it would be impossible, or undesirable, to 
pass through a fan. 

(3) Induction System. A compressed air injector 
is used to produce a partial vacuum on the suction 
or inlet end of the pipe system, and to produce 
a pressure above atmospheric at the delivery end, 
thus avoiding the necessity for a discharger. This 



8 PNEUMATIC CONVEYING 

system, which is suitable for use with heavy sticky 
materials such as hot sugar, saturated sand, 
finely ground heavy ores, spent oxide as used in 
gas works, etc. is now being developed so as to 
make possible pneumatic conveyance of all manner 
of materials which are unsuitable for passing 
through the discharger, or air lock, of a suction 
system. 

Factors influencing Design. In the strict sense 
of the term, " pneumatic conveying " really im- 
plies the conveyance of a quantity of material from 
one point to another, using air as the conveying 
agent. As will be seen from the above, the 
subject also embraces the removal of compara- 
tively light dust produced in many industrial 
processes. Although the same name is implied 
in both cases, the methods to be adopted vary, 
and each case must be considered on its own 
merits. 

With regard to a conveying plant proper, the 
points for consideration in the initial stages are 
as follows 

(1) The nature of the material to be handled and 
the quantity required in a given time. 

(2) The size of the largest and smallest pieces 
of materials and the density of the material. 

(3) The distance over which the material is to 
be conveyed. 

(4) The difference in level between the point at 
which the material is fed into the system, and the 
point where it is delivered. 



SYSTEMS OF PNEUMATIC CONVEYING 

(5) The method and regularity of feeding the 
material into the system. 

(6) The means to be adopted for separating the 
material from the conveying air at the desired 
point of delivery. 

There is a very important distinction between 
plants in which the material passes through the 
fan or blower and those in which the conveying 
is carried out entirely under suction. 

The latter system has many advantages, but it 
carries with it the necessity of providing automatic 
delivery of the material without seriously impairing 
the suction. In order to accomplish this, some 
form of " air lock " is required, and a necessary 
feature of this is a device with close-fitting surfaces 
or more or less air- tight valves. The simpler plan 
is undoubtedly to pass the material through the 
fan, as there is then no question of breaking the 
suction in order to get the material out of the 
system. It is common practice to convey for long 
distances such materials as wood chippings and 
sawdust, cotton, jute, wool, esparto grass, paper 
chippings and many other materials. In all cases, 
however, the designer is confronted with the 
problem of separating the material from the air, 
and in many instances to do this satisfactorily is 
more difficult than the actual conveying ; especially 
is this so with certain sticky materials or materials 
which will readily " pack " or build up when 
entering any mechanical discharger at the high 
velocity necessary in the suction system. 



CHAPTER II 

DETAILS OF PLANT 
PUMPS, EXHAUSTERS AND AIR FILTERS 

A PNEUMATIC conveying plant of practically any 
type comprises the following five main components : 

(1) A pump or exhauster to create a partial vacuum 
in the pipe line and so induce a high velocity air 
current in which the material will be conveyed. 

(2) An air filter in which any light dust carried 
over beyond the receiver is trapped, to prevent 
its entering the exhauster where it would quickly 
damage the piston rings and cylinder walls of 
reciprocating pumps. (3) A main receiver or dis- 
charger, and occasionally one or more subsidiary 
receivers, in which the conveyed material is 
extracted from the system and discharged into 
the receptacle or on to a dump as required. 

(4) The pipe line, junctions, etc., to connect the 
point of supply with the desired point of delivery. 

(5) The suction nozzle through which the material 
enters the system, together with the " free air " 
which is to act as the conveying medium. 

Pumps and Exhausters. The type of apparatus 
used for creating the flow of air varies according to 
the ideas of the numerous makers of the plants. 
It must be remembered that for a pump working 
under the conditions required for pneumatic plants 
it is not a high vacuum that is required ; the most 
10 



DETAILS OF PLANT, ETC. 11 

important function is to handle very large 
quantities of air at a comparatively low vacuum. 

The most efficient type of plant for dealing with 
large quantities of air is certainly the reciprocating 
pump, although several makers are now devoting 
a lot of attention to the multi-stage turbine type 
of blower, or exhauster. The probability is that 
this type may shortly be as efficient as the re- 
ciprocating pump, and if so it is almost sure to be 
used extensively, as it has distinct advantages in 
other directions compared with the cylinder and 
piston type. This remark has special reference 
to the high pressure system for conveying sand, 
coal, sugar, etc., and does not apply to the " small 
pipe system " detailed later. 

In dealing with ashes, flue dust, crushed iron ore, 
and similar abrasive materials, it is essential that 
the air passing through the pump should be 
filtered thoroughly so that no dust should enter 
the cylinders and cut the walls and piston rings. 
The turbo-blower, having no rubbing surfaces, 
would suffer little or no damage from a small 
percentage of dust, hence the filtering equipment 
might be less elaborate and less costly. No 
lubrication would be necessary in the rotary pump 
(except, of course, at the bearings), hence no 
difficulties would arise owing to oil acting as a dust 
trap, as is sometimes the case in reciprocating 
pumps with defective air filters. 

Typical Reciprocating Pump. Fig. 1 shows the 
general construction of a vertical steam-driven air 




FIG. 1. KING'S PNEUMATIC SYSTEM. STEAM-DRIVEN 
AIR PUMP, 



KEY TO FIG. 1. 

A = cylinder of double-acting steam engine driving the whole 
macliine. 

B = semi-rotary valve controlling admission of steam to A. 
C = steam gland for piston rod connecting L and M . 

D = Corliss-type air-inlet valves with semi-rotary motion. These 
valves are alternately open to the pipe system and the air 
cylinder E when the p : ston is travelling in ooe direction, 
and are closed (both to cylinder and air pipe) directly the 
piston reverses its travel. 

E = cylinder of double-acting air pump. 

F = valve gear for operating the Corliss valves, D this gear is 
driven by a pin out of centre on the flywheel. 

G = cross-head and slide. 
H = big-end bearing and crank. 
I = flywheels on the main shaft. 

j = eccentric and strap operating the valve, 13, on the steam 
cylinder. 

K = leather air-outlet valves held on two sides by metal strips. 
The leathers are opened by air pressure on the exhaust 
stroke, and are drawn on to their gridiron seatings during 
the inlet stroke. 

L = steam piston. 
M = air piston. 

Note. If preferred, the steam cylinder may be omitted and the air 
pump driven by electric motor direct-coupled or geared to the main 
shaft. Belt drive on to the flywheels or special pulley is possible but 
not advisable. 



14 PNEUMATIC CONVEYING 

pump such as is generally used in present-day 
plants. The pump shown has a stroke of 14 ins., 
with an air- cylinder diameter of 28 ins. The 
machine is a dry air pump, and is fitted with 
Corliss inlet valves and special leather exhaust 
valves : it is fitted with ring- oiling bearings and 
automatic continuous lubrication, and under test 
it shows a mechanical efficiency of 78 per cent, 
from power input to air horse-power delivered. 
Such a pump is suitable for a plant handling 
20 to 25 tons per hour and, if preferred, the 
pump may be driven through gearing from an 
electric motor on the same bed-plate. 

Rotary Blowers and Exhausters. The turbine 
blower and exhauster depend entirely upon cen- 
trifugal force for their power to compress or 
exhaust air or gas, etc. The use of centrifugal 
force makes this type of machine resemble the 
centrifugal water-pump, but radical differences in 
design have to be introduced, seeing that water 
is not compressible, whereas air is capable of com- 
pression, and alterations are also necessary, due to 
the great difference in specific gravity of the two 
substances. 

Owing to the very low specific gravity of air, 
the machine must run at a much higher speed than 
would be required with water to develop a given 
pressure. The high speed of the steam turbine 
has given impetus to the design of large exhausters 
on the turbine principle. 

It will be recognized that, when air is made to 



DETAILS OF PLANT. ETC. 15 

flow steadily along a conduit or pipe of gradually 
diminishing cross-sectional area, the velocity of 
the air must increase correspondingly, in order 
that the constant quantity may flow through the 
smaller section of pipe. Increasing the velocity 
will diminish the pressure due to the greater 
kinetic energy to increase the velocity. The 
converse is the result of passing air at 
constant pressure through a channel gradually 
increasing from a smaller to a larger area, the 
velocity being then reduced and the pressure 
increased. 

Now if a number of impellers be mounted turbine 
fashion on a high speed shaft, and the casing be so 
designed that the area between stages gradually 
increases, the air will enter the first stage and will 
be caught up by the impeller and accelerated until 
it leaves No. 1 impeller at a higher pressure and 
velocity. Leaving the casing through a diffuser 
which gradually increases in area the velocity is 
transformed into pressure in the diffuser. The 
air therefore travels to the second stage with 
its initial pressure plus the pressure due 
to the conversion of velocity in the first 
diffuser. This process may be repeated stage 
by stage until almost any desired pressure is 
obtained. 

As there are no rubbing surfaces in this type of 
machine it is particularly suitable for the work 
under consideration, and when developed for 
efficient running in small sizes it will be very 
effective in " booming " pneumatic conveying. 



16 PNEUMATIC CONVEYING 

Sturtevant Blower or Exhauster. The Sturte- 
vant Engineering Co., Ltd., has developed a special 
rotary blower or exhauster suitable for use with 
pneumatic conveying installations and, although 
this machine has not a water-seal for surfaces 
under pressure (as in the Nash Hydro-Turbo 
described below), it has a number of distinctive 
points, and the discharge of the air, or the intake 
of air, as the case may be, occurs at a more nearly 
constant pressure and with smaller pulsations than 
with any other rotary blower known to the writer. 

The sectional diagrams (Fig. 2) show the four 
successive stages in the movement of the rotors. 
In position (1), chamber D has been filled with air, 
while chamber E is discharging air against pressure 
in the delivery pipe. In position (2), chamber D 
is cut off from the inlet, and the air in it is being 
carried round. Blade C has entered pocket Z, 
which is filled with air under pressure; this air, 
however, in turn is released into pocket Y through 
leakage passage O. Continued rotation carries the 
rotors A, B and C to position (3), and the remain- 
ing pressure in Zi is now being transferred to X 
by leakage passage N. 

As the fourth position is reached, chamber F is 
filling and pocket 7 is discharging its air. When 
further rotation brings impeller blade B into the 
discharge passage, the air in space D will be 
delivered from the blower. After leaving position 
(4), the rotors again reach a position similar to 
that shown at (1), and the cycle is then repeated. 

A study of the above will convince the reader 




Position (3) Position(4) 

FIG. 2. STUBTEVANT ROTARY BLOWER. 



18 PNEUMATIC CONVEYING 

that this blower is ingenious and very suitable for 
the class of work under investigation. 

For certain conditions the Roots blower and the 
multifarious types of drum pumps or blowers can 
be used, seeing that it is quantity rather than 
pressure that is required, but it is essential that 
the most reliable and efficient exhauster should 
be installed in accordance with the conditions for 
each installation, bearing in mind always the 
questions of dust, speed, lubrication, etc. 

Nash Hydro-Turbine. An entirely new type of 
rotary exhauster was recently illustrated in the 
Chemical Age, and a study of Fig. 3 will show the 
principle of this pump. This pump was built just 
before the war by Messrs. Siemens-Schuckert, and 
similar pumps are now being introduced by the 
Nash Engineering Co. (U.S.A.), and are known as 
the Nash Hydro-Turbine. 

This exhauster has a cylindroid external casing, 
inside which is a shaft carried on the two end 
brackets and having mounted upon it a crude type 
of water-wheel. It should be noted here that this 
arrangement has the effect of bringing the edges 
of the wheel into a position of ercentricity in 
relation to the inside of the external casing. 

The wheel shaft is connected directly to a high 
speed electric motor, and when the pump is running 
the water which is fed into the casing is thrown by 
centrifugal force to the periphery of the casing and 
thus forms certain air pockets into which the air 
of the system is drawn. The air is now locked 



DETAILS OF PLANT, ETC. 



19 



between the hub of the wheel and the sheet of 
water surrounding the outside of the wheel. As 
the wheel revolves, the air in each pocket in turn 
is compressed into a smaller capacity and eventu- 
ally, when it arrives opposite the outlet point, 



^Clearance 



Inlet Port 
Water 

Outlet Port, 




FIG. 3. NASH " HYDRO-TURBO " EXHAUSTER. 

it at once escapes into the atmosphere due to its 
additional pressure. 

Tracing the wheel right round we then find that 
another pocket is formed into which the air is 
again sucked, and so the cycle of operations 
continues, two compressions and extractions 
occurring per revolution of the spindle. For many 
materials such a pump has the great advantage 
that the water acts as, a wet filter and traps all 



20 PNEUMATIC CONVEYING 

the dust in suspension which can be washed out in 
the form of sludge. Where the dust is valuable 
this characteristic would be a disadvantage, but 
it is very useful in plants dealing with corrosive 
and abrasive materials. 

Lubrication. The lubrication of cylinders in the 
reciprocating type of pump has been mentioned in 
connection with the necessity for taking special 
care in filtering all dust from the air pulled over 
from the discharger. Ordinary oil makes a sticky 
surface to which any dust adheres readily, and the 
two combined make an abrasive mixture which 
will quickly score and damage the walls of the 
cylinders. One firm, at least, has gone a long way 
towards removing this trouble by inserting pieces 
of solid graphite into the piston : this provides 
dry lubrication and produces a very smooth surface 
on which dust finds great difficulty in obtaining 
a " footing." 

The use of " Aquadag " is also fairly successful : 
this lubricant consists of deflocculated graphite in 
such very fine particles that they will remain in 
suspension in water even without mechanical 
agitation. " Aquadag " is fed into the cylinders 
in the same way as oil and deposits its graphite 
in the pores of the cylinder walls, whilst the water 
is atomized and blown out with the air. 

The turbine exhauster solves the problem by 
eliminating the necessity for internal lubrication, 
and the perfect filtering of the air is then not so 
important. 



DETAILS OF PLANT, ETC. 



21 



Air Filters. It is impossible to deal with prac- 
tically any granular material without carrying 
over more or less dust beyond the discharger, 
and to obviate the damage and inconvenience 
which would result from allowing this to enter the 
exhauster, an air filter is fitted between the dis- 
charger and the pump. Many types of air filters 
have been introduced, and representative examples 
are described below. 

" Cyclone " Separators. For such materials as 
grain, malt, etc., the ordinary type of cyclone 




FIG. 4. STURTEVANT " CYCLONE " DUST 
SEPARATOR. 

separator is frequently mounted inside the receiver. 
This separator consists of an inverted cone : the 
dust laden air enters at the top and the heavy 
material circulates inside, and gradually falls to 

3 (5362) 



22 PNEUMATIC CONVEYING 

the bottom from which it is discharged into 
suitable containers (see Fig. 4). 

The cyclone is an excellent separator, and has 
the advantage that it is self -cleaning, and offers 
little or no resistance to the flow of air, but so 
large a cone would be required to separate very 
fine dusts that it frequently becomes impossible 
to use this type of plant. 

Bag Filters. An alternative type of air filter is 
the ordinary bag filter, which consists of a number 
of closely woven fabric " stockings " in a cast 
iron container. The air is led into the casing so 
that it passes down through the inside of the tubes, 
through the fabric, where it deposits the greater 
proportion of the dust, and then out to the 
atmosphere. 

Naturally, after working a certain period, the 
fabric becomes choked with deposited dust, and 
it is then necessary to dislodge the dust by shaking 
the " stocking " somewhat violently. This is 
usually carried out by a mechanically operated 
vibrating apparatus, but cleaning is done more 
effectively and time is saved if the air is shut off 
from the filter while the dust is dislodged. This 
is done most conveniently by having two similar 
filters installed, working in parallel ; then, when 
cleaning becomes necessary, all the air is passed 
through each filter in turn, whilst the other is 
cleaned. 

The bags or tubes hang vertically in the casing, 
and as the air is brought in at the top and 



DETAILS OP PLANT, ETC. 23 

discharged in a downward vertical direction, it 
naturally discharges the heavier material straight 
into the bottom of the casing, owing to the inertia 




FIG. 5. AUTOMATIC BAG FILTER. 
Showing filter bags through the open access doors 

of the heavy particles and the high velocity of the 
incoming air. 

Fig. 5 illustrates a Sturtevant automatic bag 
filter. In this case the air is brought in at the 
bottom. The cleaning of the bags is effected auto- 
matically. At frequent intervals and in rotation, 
each section of bags is cut off automatically 



24 



PNEUMATIC CONVEYING 



from the supply of dust laden air by closing the 
outlet valve of that section. At the same time, 
that section is opened to the atmosphere at the top, 
causing a reverse current of air downwards. The 
bags are then agitated automatically and the dust 
adhering to the fabric drops, and is blown into the 
discharge hopper below. The opening and closing 
of the valves is accomplished by a simple mechan- 
ism driven by the pulley shown at the top of the 
illustration. Where the amount of dust to be 
handled is large and continuous it can be extracted 
from the hopper by a worm or screw conveyor, or, 
as in some other patterns, by a rotary valve placed 
in the bottom of the hopper. 

Mollers' Air Filter. This apparatus consists of 
separate fabric pockets mounted on a frame. The 




FIG. G. HOLLERS' AIR FILTER. 



DETAILS OF PLANT, ETC. 25 

pockets are rectangular and taper towards the top. 
Referring to Fig. 6, A is the frame on which the 
fabric is stretched, and B is the fabric pocket. 
As many of these units as necessary are mounted 
side by side in an adjustable frame, each unit 
having fixing and tension bolts. This arrangement 
permits a filter of any desired capacity to be built 
up quickly, and facilitates repairs and cleaning 
of filter bags. 

Wet Filters. The type of filtering apparatus used 
for dealing with poisonous material, emery dust 
from grinding wheels, sand from sand-blasting 
apparatus, etc., is usually of the wet type, of which 
Fig. 7 is a good example. This apparatus consists 
of a tank having a wire shelf on which a layer of 
coke is supported. The tank is partially filled 
with water, the level of which is regulated by an 
overflow. 

The dust-laden air impinges on the surface of 
the water, and the major portion of the dust is 
trapped by being driven actually into the water. 
The dust particles too light to be brought into 
contact with the water are compelled to pass 
through the coke screen and are there arrested. 
If necessary, the scheme can be made to deal with 
finer dusts by having the coke constantly sprayed 
with water. The dust is reclaimed from the tank in 
the form of sludge or mud through the door or 
valve provided for that purpose. 

Another type of air filter which might be devel- 
oped in connection with the pneumatic handling of 



26 PNEUMATIC CONVEYING 

material consists of a very slowly revolving drum 
or cylinder, which is fitted with a continuous 
corrugated tape running spirally from the centre 
to the extreme edge of the casing. The space 
between the corrugated sheets is very small, and 




FIG. 7. STUBTEVANT WET FILTER. 

as a stream of water is continually running over 
and around the divisions, the air passing through 
the very tortuous path provided is bound to 
come into contact with these wet surfaces and 
give up its dust or other contamination, which is 
washed off when it arrives at the bottom of the 



DETAILS OF PLANT, ETC. 27 

cylinder. Naturally, this or any other wet filter 
would not be used where the recovery of dust in 
dry form was desired. 

Another form of wet filter consists of a chamber 
of suitable proportions (according to the amount 
of air to be cleansed), fitted with racks in which are 
placed strips of glass at an angle of 45 to the flow 
of air, and at 90 to one another. The glass 
strips have a serrated or prismatic face, and the 
air carries the dust forward into the angles of the 
glass. A very fine water spray keeps the glass 
moist and eventually trickles down to the drain 
channels, washing the glass in its course. 

The development of apparatus for air-washing 
has received considerable attention during recent 
years, owing to the necessity of having pure, 
dust-free air for ventilating turbo-generators, etc., 
and no difficulty should present itself in obtaining 
satisfactory results for pneumatic conveying plants, 
except in cases when the collection and retention 
of dust is required. In these cases the bag or 
fabric sheet filter is the only type available. 



CHAPTER III 

DETAILS OF PLANT (Contd.) 

DISCHARGERS, PIPE LINES AND SUCTION 
NOZZLES 

Dischargers. The advocates of " blowing " 
material, instead of " sucking " it through the 
pipe, often lay great stress on the alleged diffi- 
culties of extracting the material from the system 
without allowing air leakage. This, however, has 
been overcome successfully by several designers 
and is not the serious difficulty so frequently 
suggested, providing that the material is suitable 
for this means of treatment. The only exception 
to this is, when the high velocity at which the 
material enters the discharger say, 45 to 50 ft. 
per sec. causes it to pack or bind so that it will 
not fall by gravity into the rotary valves and then 
out into the storage bins. 

The function of the discharger is to cause the 
incoming material to lose its velocity and to fall 
into a compartment which can eventually be 
discharged after it has been moved from the low 
pressure to which the chamber itself is subjected. 

This is best accomplished by the use of a rotary 

valve, somewhat similar to a paddle-wheel, which 

is revolved slowly but continuously. This wheel 

can be placed either vertically or horizontally at 

28 



DETAILS OF PLANT, ETC. 29 

the bottom of the receiving chamber ; the material 
enters the large chamber above, loses its velocity, 
drops by gravity, is caught in the box formed by 
the revolving paddle-wheel, and gradually is 
carried forward out of the chamber, eventually 
passing over an aperture through which it again 
gravitates to the bunker, silo, or other container. 
Probably the horizontal type of rotary valve is 
preferable because, owing to the increased surface 
exposed to the vacuum, the " suction " effect 
assists in holding the valve up to its seat. 

When dealing with such materials as malt and 
grain, it is an advantage to be able to inspect the 
material entering the receiver, and at least one 
maker secures this advantage by constructing the 
chamber of a glass cylinder to which are bolted 
cast iron top and bottom pieces carrying the 
necessary pipe connections and discharge valves. 
Fig. 8 illustrates this construction and also shows 
fairly clearly the method of driving or revolving 
the discharge valves. The top flange of the valve 
has a worm wheel tooth cut around its periphery 
and the actuating worm engages in this wheel, 
thereby obtaining a large reduction in speed. In 
other words, the worm can be driven by a light, 
high-speed belt and pulley, and still revolve the 
valve at a very low speed ; such gearing is smooth, 
silent running, and altogether admirable for such 
a purpose as the one under consideration. 

A very common form of separator, which is 
used almost invariably on plants dealing with 
wood shavings, sawdust and similar materials, 




FIG. 8. FIXED DISCHARGER WITH GLASS 
RECEIVER. 



DETAILS OF PLANT, ETC. 31 

is known as the cyclone or centrifugal separator. 
This is usually constructed with a sheet steel body 
with the inlet for the dust-laden air at the top, 
and so arranged that the air enters tangentially. 
Inside there is a smaller cylinder of sheet steel 
forming an air outlet, and the laden air sweeps 
round the annular space between the body and the 
inner cylinder. This results in a whirling action 
and the material entrained in the air is projected 
by centrifugal force against the side of the separator 
body. In some instances an internal ledge, or 
plate of " corkscrew " form, leads the material 
downwards towards the outlet at the bottom of 
the separator. 

In the case of some of the denser materials which 
can be conveyed by air, it is sufficient to connect 
the discharge pipe to an open bin or chamber, the 
material in such cases being heavy enough to 
separate itself by the action of gravity. 

Mr. Gordon S. Layton, describing dischargers in 
his paper, before the Engineering Group of the 
Society of Chemical Industry (Birmingham, April, 
1920), stated 

" There are two types of dischargers hi use : 
The first consists of a large steel box divided 
into two compartments. This box is arranged 
to oscillate about a horizontal axis, so that each 
compartment alternately is brought under the 
lower opening of the receiver vessel. 

" The other type of discharger consists of a 
bucket wheel rotating continuously inside a 
closely fitting casing. The material which is 



32 PNEUMATIC CONVEYING 

being conveyed falls into the pockets of the 
bucket wheel when these are on the top of their 
revolution, and is passed out through an opening 
in the lower side of the casing. 

" It will be obvious that the working of both 
types is liable to be interrupted by the jamming 
of a foreign body (such as a piece of wood or a 
bolt) in the working parts ; in each case, special 
mechanism for driving the discharger has been 
devised, to avoid the interruption resulting from 
such blocking, and to enable the discharger to 
keep on working continuously." 
The rotary type of discharger is preferable to 
the tipping box type, for the following reasons : 
because the rotary discharger is more easily kept 
air-tight, works without vibration, and gives a 
practically continuous stream, whereas the dis- 
charge from the tipping box occurs as large isolated 
masses of material. 

It is impossible to give specific details concerning 
the discharger because, in all cases, the conditions 
under which the plant has to work affect the whole 
design. For instance, where the working is only 
intermittent, e.g. the removal of ashes from a 
boiler-house, the discharger can be eliminated, 
provided that the ash bunker is large enough to 
hold the quantity of ashes to be dealt with at 
each operation. In such a case, the ash container 
would be capable of being exhausted, and the 
material entering as before would simply drop 
by gravity into the container and remain there 
until the pump was shut down ; it would then be 



DETAILS OF PLANT, ETC. 33 

allowed to gravitate into the truck or other 
conveyance for disposing of the ashes. 

Hand-holes for cleaning, and easy access to the 
interior are essential in the design of a discharger, 
especially if the material to be handled is liable to 
" pack " when entering at a high velocity. 

Pipe Lines. One of the most important points 
in the designing of a pneumatic conveying system 
is the correct lay-out of the pipe line. 

A fatal mistake often made in low pressure and 
exhausting systems is that the numerous branch 




FIG. 9. STURTEVANT PATENT JUNCTION. 

pipes are added to or altered after the makers 
have left the original installation. Almost in- 
variably, branches thus added are made to 
approach the main trunk at too great an angle, with 
the result that eddies and whirlpools are created 
within the pipe, seriously reducing the output of 
the main trunk. So essential is it that this junction 
should be correct and that the two streams should 
run as nearly parallel as possible, that the Sturte- 
vant Engineering Co. has patented a special 
junction (Fig. 9) to bring together the two streams 
of air in the main and the branch pipe practically 
parallel, as shown. 



34 PNEUMATIC CONVEYING 

Bends. In connection with high pressure sys- 
tems, the following points are of great importance. 
All vertical and horizontal straight lengths may 
be of a light section constructed in steel. Bends 
should be avoided whenever possible, and those 
which are inevitable should be made in hard cast 
iron, with every possible provision for easy 
replacement of wearing parts. 

The wear takes place at the point of actual 
contact which, in elbows, is practically confined 
to one place only. The material rushes to the end, 
strikes the bend, and suddenly changing its 
direction of travel whirls off down the next 
straight length. The impact and the resulting 
wear on the pipe, as well as the breaking of the 
material conveyed, are naturally much greater in 
elbows than in easy bends, but if the breaking 
of the material is not detrimental, elbows should 
be employed, as they are less costly and can be 
rep^ced more quickly and easily. 

Certain raw materials such as salt, soda, lime 
and various chemicals which have to be ground 
before use, may be prepared to a considerable 
extent for this operation by the use of elbows. 
On the other hand, easy bends should be employed 
for material which it is desired to convey without 
damage, e.g. malt, coal, and granular substances, 
which are finally required in granular form and 
not as powder. 

The wear in bends is only on the external 
radius of the bend, and then is inclined to be 
localized at certain points rather than distributed 



DETAILS OF PLANT, ETC. 35 

over the full sweep of the bend (see Fig. 10) ; 
this being so, it is often desirable so to construct 
the bends that the back is in segments which can 
be renewed easily (see Fig. 11). Alternatively, 
the bend may be constructed on the " lobster " 




Fig. 10. Fg. 11 FigM2. 

FIG. 10. COURSE TAKEN BY MATERIAL ROUND 

BEND. 

FIG. 11. SEGMENT-BACK BEND. 
FIG. 12. LOBSTER BEND. 

principle (Fig. 12), only the worn sections being 
replaced when overhauling. It is not necessary 
always to take a bend at an angle of 90, and if 
the small short angle sections are interchangeable, 
then almost any angle can be constructed by 
building up with the necessary number of sections. 
With regard to the straight lengths of pipe, it 
is necessary to ensure a smooth internal bore, 
especially at the joints. It is therefore desirable 
that the joints should be self -aligning as, if this 
is not the case, eddies will be formed which will 
cause the material to deviate from the centre of 
the pipe, striking the side at one or more definite 



36 PNEUMATIC CONVEYING 

points where holes will eventually be worn through 
the pipe. 

In vertical pipes the evidence of wear is negli- 
gible, in fact the conveyed material presumably 
does not touch the pipe at all, but travels up the 
centre of it as a core. 

Capacity of Pipes. The velocity of the air 
passing up the pipe should be from 40 to 50 ft. 
per sec., equivalent to about 35 miles per hour. 

The conveying capacity of an efficient pipe-line 
is approximately 15 per cent, of the total capacity : 
in other words, if the total cross -sectional area 
of the pipe be taken as 100, the effective cross- 
sectional area as regards conveying is 15. 

Flexible Connections. The flexible connections 
attached to the permanent pipes may be ordinary 
tubing, as made by the Flexible Metallic Co. 
Phosphor bronze and other metals have been tried, 
but the extra cost is not justified. A loose screw 
collar connection makes possible easy fixing, and 
permits the flexible connection to be removed 
easily to prevent damage when not in use. Rubber 
tubing, reinforced with steel wires, would be best 
where it is important that the material conveyed 
should not be damaged, but the wear on such 
tubing is so rapid that the extra cost is not re- 
covered by the saving in damage to ordinary 
materials. The length of the flexible pipe should 
be such that the movement over the greatest 
area to be covered does not put too great a strain 



DETAILS OF PLANT, ETC. 



37 



on the bending properties of the tubing. On the 
other hand, unnecessary increase in the length 
of the flexible pipe merely increases the cost of 
one of the shortest lived portions of the plant, 
the " scrap value " of which is almost negligible. 

Valves, etc. For use where branches are inserted 
in the main pipe line for convenience in either 




Showing Three Positions of the Valve. 
FIG. 13. KING FULL-WAY JUNCTION VALVE. 

lifting over, or discharging over, a large area, 
special appliances have been designed and these 
should be used, as they do not create eddies or 

4 (5362) 



38 PNEUMATIC CONVEYING 

increase the pipe friction appreciably, or reduce 
the carrying capacity of the pipe line. The King 
patent full- way junction valve is an excellent 
example, and is shown in Fig. 13, from which 
it will be seen that a full bore circuit can be com- 
pleted in any of three directions. This valve has 
no corners where the material can collect, hence 
the pipes are sucked perfectly clean the moment 
the feed is shut off. 

Another convenient fitting of this description is 
the Boby patent pipe switch. This device is 
similar to a switch as used on a railway track, 
and by its use three separate side positions may 
be connected with one part on the main transport 
line. When the switch is thrown over so as to 
connect to any one particular branch, all other 
branches are disconnected. 

Telescopic Pipes. When the unloading of ships 
is carried out by " suction " it is necessary to 
make provision for lengthening or shortening the 
vertical suction pipe, or pipes (see Frontispiece), 
because the ship will rise as relieved of its cargo, 
and the suction nozzle will simultaneously move 
towards the bottom of the hold as the cargo is 
discharged. 

A still greater difficulty is encountered in tidal 
rivers, where the rise and fall may be many feet and 
must be allowed for continuously. This is best 
done by the introduction of telescopic pipes in 
the vertical downright pipes. These must be so 
constructed that while it is fairly easy to increase 



DETAILS OF PLANT, ETC. 39 

or decrease their length, the pipes must remain 
air-tight at the joints and connections. 

Where the rise and fall is small the difference in 
level may be compensated by a ball and socket 
joint, and a counter balance on the jib arm, but 
this method has its limitations. 

Pipes for High Pressure Systems. Coming now 
to the " small pipe," high pressure systems as 
used for vacuum cleaning plants, the pipe lines 
must be designed and installed carefully and on a 
liberal basis. It is mistaken policy to attempt 
to economize by using a smaller main on branch 
pipes. Small diameter pipes cause excessive 
losses by friction, and naturally are less efficient 
as regards power consumption. 

The frictional losses in a system of this descrip- 
tion vary directly as the length of the pipe, and 
inversely as the fifth power of the diameter. 
Large pipes are therefore very desirable, not only 
because of their greater carrying capacity which 
is very desirable but also because such things 
as matches, hairpins, etc., are picked up every 
day by an installation as fitted in hotels, restaurants 
and theatres. Such material quickly clogs small 
pipes and causes endless trouble and delay. 

The flexible hose should be as short as is con- 
sistent with ease of working, because the frictional 
losses in this class of tubing are very great. It 
would be preferable to increase the number of 
wall plugs, rather than have to use very long 
lengths of flexible hose. 



40 PNEUMATIC CONVEYING 

Suction Nozzles. Probably more patents have 
been taken out on new suction nozzles than on 
any other portion of a pneumatic suction plant. 
The chief desiderata for a nozzle on a high pressure 
system for wheat, coal, ashes, etc., are that it 
be of light construction to allow of easy manipula- 
tion by the operator, and that it have some means 




FIG. 14. SUCTION NOZZLES FOR HIGH PRESSURE 

SYSTEMS. 

of allowing a " free air " inlet, making it im- 
possible to choke the nozzle by burying the end. 
It is an advantage to be able to regulate the 
free air inlet according to the conditions existing 
with different materials. The same nozzle that 
will act best while dealing with a large bulk of 
material, may be quite unsuitable when it becomes 
necessary to " clean up " in the corners of the hold 
or waggon. Fig. 14 shows different types of nozzles 
for high pressure plants, but as the efficiency 



DETAILS OF PLANT, ETC. 



41 



and capacity of the plant can be affected 
seriously by the design of this portion of the 
apparatus^ it is highly advisable to allow the 
designer to have a free hand and to make use of 
the experience already gained. 




FIG. 15. STURTEVANT EQUIPMENT REMOVING WOOD 
REFUSE FROM DOUBLE TENONING MACHINE. 

Nozzles designed for low pressure systems, dealing 
with dust, shavings, etc., have to be built to suit 
the machine to which they are attached, and they 
therefore vary indefinitely in details of design and 
construction. The same remarks apply to the 
nozzles for use on suction cleaning plants. Figs. 
15 and 16 show how the suction nozzles are adapted 
to the machines. 



42 



PNEUMATIC CONVEYING 



It must be remembered that in low pressure 
systems handling shavings, dust, etc., the problem 
is quite different from that in high pressure 




FIG. 16. STURTEVANT EQUIPMENT REMOVING DUST 
FROM SAND -PAPERING MACHINES. 

systems handling wheat, etc. In the case of re- 
moving dust or shavings from a machine, the 
material is already in motion, and only requires 
drawing forward and into the pipe system, but in 
the case of conveyors for wheat, coal, etc., and in 
the case of suction cleaners, the material to be 
moved is heavy and stationary and has to be lifted 



DETAILS OF PLANT, ETC. 43 

and started in motion before it can be carried 
away. This necessitates a much higher air velocity 
through the collecting nozzles. 

Idle Nozzles should be Closed. It is perhaps 
advisable to draw attention at this point to the 
disadvantages of using more than one suction 
nozzle on one receiver at one and the same time. 
The reader is asked to recall the fact that the 
material is not lifted by vacuum, but that the 
production of a partial vacuum causes a stream 
of air to pass up the pipe at high velocity. The 
material to be conveyed is entrained with the air, 
and due to the frictional contact between the 
particles of air and the particles of material, the 
latter is lifted and carried forward. 

If the conveying plant is to be efficient and of 
reasonable capacity, the pipes must be relatively 
large, and in order that the desired partial vacuum 
may be maintained in them (establishing a vigorous 
air current) without the use of an unduly large 
pump, it is important that air be admitted only 
through those nozzles which are actually in use. 
Also, when more than one nozzle is in use at the 
same time, it is necessary to keep each nozzle 
covered with material to such an extent that the 
same amount of air passes into each pipe. Unless 
this is done a large quantity of air will pass up 
one pipe, and a small quantity up the other, and 
the amount of material taken in at each nozzle will 
vary as the quantity of air varies. To consider an 
extreme case, suppose that the man operating at 



44 PNEUMATIC CONVEYING 

one of the pipes allows his nozzle to become 
exposed. Air will rush in at this nozzle to the full 
capacity of the pump, with the result that little or 
no air will pass up the second pipe, and conse- 
quently no material either. Thus, if one man is 
sufficiently neglectful to leave his nozzle idle and 
open, he renders practically useless the other 
nozzle or nozzles on the same main. 

Even with care this is bound to occur to a certain 
extent, as is shown by the figures given by makers 
for the estimated power consumption, viz., about 
1 h.p. per ton on single-nozzle plants, and 1 J h.p. 
on double-nozzle plants. 

Under these conditions it should be considered 
whether it is more advisable to install one large 
plant with two nozzles, or two small plants, each 
with only one nozzle. The decision depends upon 
the extra cost of power for the double-nozzle 
plant compared with the higher capital charges 
on the two single-nozzle plants. 



CHAPTER IV 

TYPICAL INSTALLATIONS FOB GRAIN 

THE pneumatic principle has been applied to the 
handling of grain in bulk to a much greater extent 
than to any other material. As previously stated, 
the original successful plant invented and designed 
by Mr. Frederic Duckham was for the handling 
of wheat for the Mill wall Docks Co., and the 
success of this plant was such that it was imitated 
by engineers in this country and abroad with 
equally satisfactory results. 

Grain lends itself admirably to pneumatic 
transport because it is easy of flow, regular in 
size, and practically self-feeding. Also, the re- 
moval of dust, which is incidental to pneumatic 
conveying, is a special advantage where grain is 
concerned. Figs. 17 and 18 show clearly the 
advantages of pneumatic conveying in point of 
simplicity and labour saving. 

Typical Quayside Plant. Fig. 19 shows a typical 
lay-out for a comparatively small plant handling 
50 tons per hour. The diagram is almost self 
explanatory. 

A represents the special suction nozzle through 
which the grain enters the system, together with 
the " free air " which acts as the conveying 
medium. 

45 



48 PNEUMATIC CONVEYING 

B is a length of flexible pipe to enable the 
nozzle to sweep the width of the barge, the length 
being dealt with by moving the boat to within 
the radius of the swivel arm E. 

C is a permanent pipe carried on the jib arm 
which is mounted on a swivel joint ; B is another 
short flexible pipe to permit of the swivelling 
already mentioned. 

F indicates the receiver into which the grain is 
deposited, and G the special rotary valves, for 
releasing the material from the system without 
interfering with the vacuum of the conveying 
line. 

H illustrates the twin air filters which are 
provided with valves, so that each of the filters 
can be isolated in turn from the rest of the plant 
for cleaning of the fabric tubes, without 
interrupting the continuous working of the plant. 

J indicates the connecting pipes between the 
receiver, air filters, and pump, and it should be 
noted they are considerably larger than those on 
the suction end C, this being necessary to allow 
for the expansion of the air under vacuum. 

K is the reciprocating air pump, driven electric- 
ally by the motor M through large helical gear 
wheels, which act as flywheels and are helpful in 
equalizing the torque required by the pump. 

L is the outlet pipe for the air as it is exhausted 
from and by the pump. 

This plant is simple, but every possible modifi- 
cation can be added that circumstances make 
desirable ; such as discharging on to a belt 



TYPICAL INSTALLATIONS FOR GRAIN 51 

conveyor, for feeding the silos or other storage 
bins. 

Where grain is bought by bulk it would be 
necessary to check the weight, and in this case 
an automatic weigher would be installed, into 
which the material would be discharged from the 
receiver. With a bag filter the collected dust can 
also be weighed, the total weight being then 
obtained by addition. 

Typical Floating Plant. The most popular 
development of the above type of plant is the 
floating plant, designed for erection on a hulk, or 
barge, and intended to suck grain from an ocean- 
going steamer and discharge it into barges or 
lighters on the other side of the discharging plant, 
as indicated in Fig. 20. The plant shown is one of 
many in actual operation and its construction 
may be followed by reference to the description of 
the plant shown in Fig. 19, the same index letters 
being used in each case. One great advantage 
of floating plants is that the difference in height 
due to tides is of no consequence. 

Portable Plants. Still another modification con- 
sists of a complete quay- side plant mounted like 
a travelling crane, so that it can be moved longitu- 
dinally along steel rails on the quay- side. This 
plant is particularly useful where large cargo ships 
have to be emptied and then allowed to remain at 
their berth until reloaded with another cargo. 

Complete plants have also been mounted on 



TYPICAL INSTALLATIONS FOB GRAIN 53 

railway trucks, the engine and pump in this case 
being on a second waggon (see Figs. 21, 22). In 
such a case the plant has to be mounted very low, 
and it is necessary to lift from the under- side of 
the truck to, say, a railway waggon, by means of 
an adjustable belt or bucket elevator (shown at 
the extreme left of Fig. 21). 

Many other applications will suggest themselves 
to the reader, and sufficient has been said to prove 
that for the handling of wheat the pneumatic 
system is distinctly flexible and convenient ; also, 
it effects a great saving in labour, which is an 
important consideration nowadays. " Bushel- 
ling," conveying, and weighing by hand used to 
cost well over a shilling per ton, which figure was 
reduced to just over IJd. per ton by pneumatic 
conveying ; these are pre-war costs in both 
instances, but the relative saving effected by 
pneumatic conveying is certainly not less under 
present conditions. 

All the previous remarks also apply to Unseed and 
cotton seed in bulk, maize, oats, and in fact all 
cereals. Such materials have to be accepted as 
and when the ships arrive irrespective of con- 
venience, and it is an important advantage of 
pneumatic conveying that the material can be 
lifted and discharged in the most convenient 
position ; also, when the barge or ship has departed 
the same apparatus can be utilized to lift the 
material from its position in store to the cleaning 
or grinding plant. 

5 (5362) 



CHAPTER V 

PNEUMATIC COAL- HANDLING PLANTS 

THE writer was directly interested in the erection 
and installing of one of the first plants installed in 
this country for the elevation and conveying of 
coal, and a description of the various details may 
give a good idea of a complete plant, handling 
coal on a commercial scale. 

The 'conditions to be complied with are as 
follows : 20 tons of " slack " per hour, to be 
raised 90 ft. above canal level or 80 ft. above 
road level. 

The coal is brought alongside the power-house by 
canal barges of 25 tons capacity, or by tipping 
steam waggons from the railway sidings, a distance 
of one mile away. In both cases the coal is 
required to be elevated into overhead bunkers 
of 600 tons capacity placed vertically over the 
boilers. 

In the first case, immediately the barge is along- 
side, the flexible suction pipe is lowered into the 
barge (Fig. 23), and coal immediately begins to 
rise in the pipe and is discharged as required. 
Little or no handling of the coal is required after 
the suction nozzle has once reached the bottom 
of the barge ; all that it is necessary to do is to 
bring the barge gradually up to the nozzle, the 
coal then " avalanching " down to the nozzle., 
54 




FIG. 23. PNEUMATIC UNLOADING OF COAL AT 
MESSRS. BOOTS, LTP, (NOTTINGHAM). 



56 PNEUMATIC CONVEYING 

Fig. 24 shows the discharger placed on 'girders 
over the bunkers into which it discharges con- 
tinuously. The coal enters at A and the major 
portion of the fuel is discharged through the 
rotary valves B. 

The coal discharger itself consists of a cast iron 
vessel with two King's patent rotating valves. 
These are designed in the form of a slightly conical 
taper divided into four sections, one portion of 
the circular valve being under vacuum, and the 
other under ordinary atmospheric pressure. The 
outlet of the valves is larger than the inlet to allow 
the coal which is in the valve to drop out easily. 
Over each valve is also provided a four- armed 
sweeper to prevent any damp coal from forming 
a cone inside. The discharger is provided with 
two inlets with full- way bored valves, so that the 
coal can be drawn either from the water side or 
from the land side at will. After the coal has been 
deposited in the main discharger, there is provided 
a supplementary discharger consisting of a vessel 
6 ft. high by 30 ins. diameter, with two inlet pipes 
of 8 ins. diameter, to provide a contra-flow, so 
that any particles of coal dust in the air will 
meet one another in the 30 ins. box at equal 
velocity and be deposited. The small particles 
are delivered by a supplementary rotary discharge 
valve which is set to run very much slower than 
the main discharger valves. 

The main discharger valves are driven by worm 
gearing, the latter having one right-hand thread 
and one left-hand thread, so that the end thrust 




FIG. 24. DISCHARGER FOR COAL CONVEYING 
PLANT. 



58 PNEUMATIC CONVEYING 

on the worms is neutralized. Ball bearings are 
provided and the small motor which drives all 
three valves is coupled up with an electrical 
device designed by the author. This device 
ensures that if anything happens to the top dis- 
charge valves so that the 3 h.p. motor driving 
them cuts out, owing to an overload or other 
cause then the main motor also is cut out by the 
opening of its circuit breaker. This prevents any 
" flooding " of the pipes and dischargers. 

It may be mentioned that the valves are so 
designed that a portion of the weight of each valve 
is carried by the vacuum, so that the vertical wearing 
lift on the valves when at work is very slight. 

The intake pipes for the coal are 5 ins. diameter, 
and they are provided with heavy cast iron bends, 
having extra thick metal on the outside radius 
to allow for the wearing effect of coal passing at 
the rate of 20 tons per hour. 

The pipe into the barge is provided with a 
flexible steel pipe at the suction nozzle end, for 
convenience of handling. India-rubber piping has 
been tried, but the extra cost does not justify 
its continued use. 

The nozzle is made as light as possible for con- 
venience of handling, and is fitted with a special 
" free air " inlet for the regulation of the amount 
of air necessary to blend with the coal. 

Ash Handling. In addition to unloading coal, 
the above plant is capable of dealing with hot 
ashes which are first crushed in a portable clinker 



PNEUMATIC COAL-HANDLING PLANTS 59 

breaker, electrically driven, which runs under all 
the ash hoppers of the boilers. The ash when 
crushed gravitates into funnel-topped tee-pieces, 
inserted in the main ash conveying pipe, whence 
it is immediately sucked up into an overhead 
ash hopper to await the convenience of the wagons 
which dispose of it on the " tips." 

Flue Cleaning. A 3 in. suction pipe has been 
run round the boiler-house in such positions that 
flexible hose can be attached for flue cleaning 
purposes. In this case the cleaners simply use 
an enlarged nozzle such as is supplied with a 
domestic equipment and the dust is removed 
from the flues, economizer soot chambers, etc., 
into the ash hopper without trouble or dust. 

The success of this plant is best indicated by 
the fact that, at the moment of writing, a duplicate 
plant is being erected. Owing to the growth of 
the business, and its demand for power and steam, 
the original plant has to be worked continuously 
* on coal, so that the ash and flue dust problem has 
become acute again. 

Portable Floating Plant. A third plant ordered 
by the same firm is of considerable interest. This 
is intended to be mounted in a barge so as to be 
portable. Owing to lack of space in close prox- 
imity to the power-house, considerable difficulty 
is found in keeping adequate stocks of coal on 
the site except the 600 tons in the overhead 
bunkers. In order to secure continuity of working, 



60 PNEUMATIC CONVEYING 

it is essential that as much fuel as possible be 
stored, and for this purpose a coal pile has been 
made about half a mile away from the works, 
adjoining the canal. Ashes can be disposed of on 
certain fields a few miles outside the city in 
swamps and pools caused by subsidences, due 
to colliery workings. 

The portable plant is therefore arranged to 
operate as follows : the barge is self-propelled by 
a 30 h.p. paraffin engine which can be coupled by 
clutches to either the propeller or a Roots blower, 
the latter being the exhauster for the portable 
suction plant. 

The barge is loaded with ashes for disposal, 
and then proceeds under its own power to the site 
where they are to be dumped. The clutch is 
operated disconnecting the propeller and operating 
the blower. The suction side of the blower is 
coupled up with the pipe line in the boat and the 
barge feeds the plant by means of the flexible 
hose : the discharge pipe is raised over the towing 
path so as not to interfere with passing traffic, 
and the ashes are blown out into the swamps 
previously mentioned. It will readily be recog- 
nized how simple this unloading becomes compared 
with trying to dig out the ashes with either a 
spade or a fork. 

The empty barge then returns to the coal pile 
and takes up a load of coal in a similar manner, 
then proceeding to the power-house under its own 
power and being unloaded by the original fixed 
pneumatic installation in the ordinary way. 



PNEUMATIC COAL-HANDLING PLANTS 61 

The coal arriving by road is tipped into a 
concrete hopper excavated below the ground level, 
and so designed with sloping sides that it is self 
feeding into a suction pipe connected to the bottom 
of the hopper. The same procedure occurs except 
that in this case the coal enters the main discharger 
at the top (E, Fig. 24). 

It is interesting to note that the very fine dust 
collected from the air filter is eagerly sought after 
by the foundry trade, and what would at first 
appear to be a waste product impossible to burn, 
is actually a valuable by-product of the plant. 



CHAPTER VI 

THE INDUCTION CONVEYOR 

NUMEROUS means have been devised to cause the 
necessary current of air to flow along the conveyor 
pipe, but the ideal method is probably yet to seek. 
Probably the most satisfactory and economical 
system, until recently, was the positive pump 
exhausting a vacuum chamber ; the latter re- 
ceiving the material, and discharging it into the 
receptacle provided for that purpose. 

The difficulties arising in practice, however, 
incited the inventive genius of engineers respon- 
sible for the operation of these plants, and a 
number of attempts were made to induce an air 
current by other means. 

Ejector Systems. Steam ejectors were fitted 
to the closed tank provided for the reception of 
the material, thus converting the tank into a 
vacuum chamber, and eliminating the discharger. 
In other cases injectors, also operated by steam, 
were placed at intervals along the conveyor 
pipe, usually at such convenient points as 90 
bends, and the slight vacuum created by the 
condensation of the steam and also by the velocity 
of the jet, induced an air current which swept 
the material along with it into the receiver chamber. 

Although both these methods are in practical 

62 



THE INDUCTION CONVEYOR 63 

use, their applications are strictly limited to 
materials which do not suffer by contact with 
heat and moisture ; the methods are therefore 
used principally for conveying ashes and soot from 
boiler furnaces and flues. Ashes formed by the 
combustion of coal contain large amounts of 
abrasive matter, and it is very important that all 
this matter should be extracted from the air, 
before entering the exhauster of the suction system. 
The steam jet cuts out the exhauster entirely, but 
absorbs an excessive amount of power in the form 
of steam. It has the advantage, however, of 
quenching the ashes on their way to the settling 
tank. For flue dust, however, the steam jet is 
unsuitable, as the condensed vapour causes the 
material to cake in the pipes, and the latter 
rapidly become choked, involving considerable 
delay and trouble in cleaning out. The ejector 
system is used for this material, the tank being 
of the closed type, and the necessary vacuum 
being created by a steam ejector fixed in a branch 
at the side near the top, the dust striking a baffle 
and falling by gravity to the bottom of the tank. 
A special air-tight gate or valve is opened to empty 
the tank. 

Air Induction. The cardinal feature of the 
induction system is the ease with which materials 
may be handled which cannot be conveyed by the 
suction method. 

Sand, sugar, salt, soda ash, and many other 
substances of a granular nature, which are very 



64 PNEUMATIC CONVEYING 

troublesome when conveyed by the suction method, 
may be dealt with economically by the induction 
system and, although the latter is only in its 
experimental stages at the moment of writing, it 
is possible that it may displace all other systems 
in the near future. 

The induction system differs from the suction 
system in that the air flow along the pipe is induced 
by a jet of air, at very high velocity, fixed at any 
convenient distance from the intake nozzle of 
the conveyor pipe, and the material conveyed is 
discharged either from an open end into an open 
container, or by some form of cyclone. The closed 
discharger or container, with its baffles and rotary 
valves or air locks, is eliminated, and the substance 
to be handled has a free and unrestricted flow 
throughout the length of the pipe. 

Advantages o! the Induction System. The 

advantages of the induction conveyor may be 
summarized as follows : (1) Low first cost, the 
power unit being the only expensive item. (2) Low 
maintenance cost, there being no moving parts and 
little wear. (3) Low labour cost, practically no 
attendance being required. (4) Flexibility and 
ease of handling. (5) High efficiency of power 
unit and reliability of system. (6) Ability to 
handle materials which are easily damaged. 

In the case of a suction plant handling grain or 
coal, the intake end of the conveyor is fairly 
flexible, and the nozzle may be operated over a 
fairly large radius, say, all over the floor of a 



THE INDUCTION CONVEYOR 65 

vessel's hold. The discharge end, however, is 
fixed, unless a cumbersome and expensive gantry 
is provided to permit of the discharge apparatus 
being moved about. Even should the discharger 
be mounted on rails, the area over which it can 
operate is limited by the rails on which it runs. 
With a large plant, this would mean that a number 
of dischargers would be required to lift from a 
ship into a warehouse or store, from the latter 
into bunkers or silos, or perhaps into trucks or 
waggons. Each discharger would require a separate 
exhauster and a separate intake, and valuable 
space would be occupied by the plant and expense 
incurred for machinery which would not be in use 
for a considerable part of the time. 

The induction system, however, is flexible at 
both intake and discharge ends of the pipe. It is 
only necessary to lower the nozzle into the material 
to be removed, and to place the delivery pipe over 
the receptacle for the material, and to turn on the 
air jet. The delivery may be handled easily while 
working, and the material distributed where 
required ; or suitable valves and branches may be 
fixed, and a number of discharge pipes used in 
turn to deliver into different bins or into various 
floors. 

The source of power for the operation of the 
induction conveyor is the ah* compressor. As every 
operating engineer is well aware, all machinery is 
kept in better condition and runs more economic- 
ally, when it is housed in proper environment and 
receives skilled attention. The compressor, in this 



00 PNEUMATIC CONVEYING 

case, need not be erected near the work, but may 
be placed some distance away, preferably in the 
power station, as the pipe line connecting the 
conveyor with the machine will have a very small 
bore, compared with the air pipe to the exhauster 
on a suction plant, and will also be inexpensive to 
erect and maintain. In the instance quoted 
above, where a number of suction and delivery 
points are required, only these small pipes need 
be run from a common main, and turned on and 
off as needed, the compressor running continuously 
at or near its most economical load. 

Construction of Induction Plant. The induction 
conveyor may be said to be a compromise between 
the suction and blowing methods. The air jet 
is fixed in the conveyor pipe at a suitable angle, 
some distance above the intake nozzle, and a 
stream of air at high velocity is passed along 
the pipe in the direction of the discharge. This 
air jet is designed carefully for the duty it has to 
perform, and its discharge entrains the free air 
in the pipe, causing it to move in the required 
direction. A partial vacuum is created in the 
conveyor pipe, behind the jet, and free air rushes 
in at the intake, carrying the material along with 
it. 

In order to effect the greatest economy in the 
operation of this plant, it is important that the 
power unit should be carefully chosen, and that 
the pipe system should be designed to give the 
full pressure at the jet. With modern multiple 



THE INDUCTION CONVEYOR 67 

stage compressors of the rotary or reciprocating 
type, working at about full load, very high efficien- 
cies can be obtained, and the pressure pipe line 
should be arranged to avoid loss by friction as 
far as possible. The receiver should be of sufficient 
capacity to absorb any pulsations, and to throw 
down oil and moisture before the air enters the 
pipes. A separator of good design should also be 
incorporated. 

Tn designing the conveyor pipe line, bends 
should be avoided when possible, by erecting the 
lifting pipes at an angle with the horizontal. It 
is not sufficiently well appreciated that bends and 
angles rapidly increase the frictional resistance 
to the flow of the conveying medium, and mean 
loss of power; in fact there is no doubt that the 
difference between success and failure in pneumatic 
conveying is largely a matter of design. Many 
substances which are otherwise quite suitable for 
handling in this manner are very fragile, and any 
friction on pipe walls or contact with metal baffles 
at high velocity, so reduces or pulverizes them 
that their value is reduced considerably. In the 
case of ashes from boiler furnaces, this effect is 
advantageous rather than otherwise, but when 
dealing with coal it is necessary to arrange the 
system so that the minimum amount of damage 
is done to the material. Some coals, such as 
Derbyshire bituminous, is not easily broken or 
abraded, and can be lifted very satisfactorily by 
the usual suction method. Welsh coal, on the 
other hand, is very friable, and if conveyed into 



68 PNEUMATIC CONVEYING 

the usual discharger, will emerge in a finely divided 
state, even though it may be fed to the intake in 
large pieces. For handling such materials, the 
induction method is most suitable, as the discharge 
end may be arranged so that the material is not 
delivered at high velocity, and does not strike 
any obstacle which would reduce it or break it up. 
It is possible to elevate potatoes and even oranges 
by the induction process, and it is quite within 
the bounds of probability that eggs may be 
delivered in this -manner, without more than the 
usual percentage of breakages. 

In conveying many materials, which are conveyed 
whilst hot, it is better if they can be kept at 
practically the same temperature at the delivery 
as when they enter the pipe. This is provided 
for by heating the air to a suitable temperature 
just before it enters the jet. 

This is also an additional source of economy in 
operation. As is well known, air, like all other 
gases, increases in volume with the temperature, 
and if the heat lost by the air cooling after com- 
pression be replaced at the jet, considerably more 
power is obtained. If the compressor is situated 
in such a position that most of the heat of com- 
pression is delivered at the jet, there is little to be 
gained by reheating. In most cases, however, the 
air has returned to normal temperature by the 
time it reaches the point where it is to be used, and, 
if a suitable air heater is installed at this point, 
the volume may be increased greatly by a 
comparatively small expenditure. 



THE INDUCTION CONVEYOR 69 

A heater consisting of tubes through which the 
air passes, these tubes surrounded by water under 
high steam pressures, offers the most convenient 
and satisfactory method of heating the air. The 
air pipes between the heater and conveyor pipe 
should be lagged in order to retain the heat. 

The pressure of the air may be increased by 
50 per cent, by heating to the temperature of 
steam at 200 Ibs. per sq. in. gauge pressure, while 
the cost will be comparatively small. Theoreti- 
cally, a gain of about 40 per cent, in economy 
should be obtained, and the practical results 
should be reasonably close to this figure. 

Air Receivers. It is a decided advantage in 
practice to instal an efficient separator between the 
ordinary receiver of the compressor and the pipe 
line, as large quantities of moisture will travel 
over with the air, and will be condensed directly 
they meet some cooler surface. The ordinary 
receiver is supposed to fulfil this function, but it 
does not do so because it is, in effect, an enlarge- 
ment of the pipe line, and, being filled with hot 
air under pressure, has no tendency to condense 
the moisture. The latter does not begin to cool 
to any extent until it reaches the small diameter 
pipes, with the consequence that these pipes 
contain quantities of oil and water which eventually 
reach the jet, and are blown into the material 
handled. 

Where compressors of the rotary or turbine 
type are installed, there will be only water in 

6 (5362) 



70 PNEUMATIC CONVEYING 

expansion, but it is good practice to remove this, 
even though the air be re-heated, because the 
moisture will recondense in the conveyor pipe, 
and tend to choke the latter when small grained 
substances are being conveyed. 

Types o! Compressors. Reference has already 
been made to the power unit, and it is hardly 
within the scope of this work to describe in detail 
the various machines available. As, however, the 
economy of air conveying depends in a large 
measure on the cost of power, it is evident that the 
compressor should be of the most suitable type for 
the duty to be performed. 

For small installations, single-stage reciprocating 
machines, driven directly by steam engines or by 
electric motors are, no doubt, the most suitable. 
In the case of large plants, using the air con- 
tinuously in a number of air jets, where the load 
factor is high, it is certainly more important to 
install a two or three-stage compressor, owing to 
the greater economy of working. The larger 
capital expenditure will be compensated by the 
considerable saving of energy. As compared with 
single-stage compression to 100 Ibs. gauge pressure, 
a saving of 20 per cent, can be effected by three- 
stage working, and with a constant load of from 
75 per cent, to 100 per cent, of full load, a turbine 
or electrically driven rotary multiple- stage 
compressor is decidedly the best type to adopt. 

In plants where exhaust steam can be used to 
advantage, as in large generating stations, a steam 



THE INDUCTION CONVEYOR 71 

turbo-compressor, multiple-stage, exhausting to a 
feed water heater will show great economy, and 
the operating costs of a large plant of this type are 
very low compared with any other form of conveyor. 
This will be obvious when it is pointed out that 
maintenance costs on the conveyor are confined 
to renewals of bends and junctions in the pipe 
lines, and of flexible hose. There are no discharge 
valves or air locks to be kept vacuum tight, no 
filter strainers or sleeves to renew, and the power 
unit is not subjected to undue wear through 
extraneous matter entering the cylinders and 
scoring the walls or wearing the valves. 

Compared with other forms of mechanical 
conveying, the pneumatic induction system is 
very low in maintenance costs, while the serious 
charges incurred in employing human labour are 
reduced to a minimum. 



CHAPTER VII 

STEAM JET CONVEYORS 

A METHOD of removing ashes from boiler furnaces 
which has been developed extensively in America 
is essentially a pneumatic system, although steam 
is the conveying medium instead of moving air. 
Steam is used because the apparatus is always 
in use on boiler plants, from which steam can be 
taken as conveying medium. No air compressor 
or other special plant is required. On the other 
hand, the simple use of a connection from the 
steam main is a matter of very little importance, 
and no check is ever made as to the amount of 
steam so used, hence 99 per cent, of the users 
consider that the steam jet costs practically nothing 
for " power " compared with a compressor which 
would have a certain sized motor connected, and 
could not escape attention as an additional power 
consumer. 

Steam Consumption. Investigation into the 
actual consumption of steam jets would often 
give very startling results, especially after the 
plant had been in operation for some time and the 
nozzles had begun to cut and wear. As proof 
of the waste of steam possible in such a plant, 
it is interesting to note that Mr. David Brownlie, 
72 



STEAM JET CONVEYORS 73 

in a paper on Automatic Stokers,* gave results 
of actual tests made on steam jets as used in 
certain classes of stokers in which steam jets are 
allowed to blow down the hollow furnace bars. 
These tests showed that, whereas the makers 
estimated the steam consumption of the jets to be 
about 2 per cent, of the boiler output, the tests on 
80 plants showed a consumption varying from 
0*5 per cent, up to as much as 2T4 per cent, of the 
total output of boiler. 

As further evidence of the waste of steam that 
can occur due to neglect of the cutting effect on 
the nozzles, one American firm has designed an 
ingenious warning or " tell-tale." A small hole 
is drilled almost, but not quite, through the nozzle. 
While the nozzle retains its initial shape and size 
the apparatus acts normally, but as soon as the 
small amount of metal covering the end of the 
hole has worn away, the hole is exposed, and a 
certain amount of steam passes through it to a 
steam whistle which blows continuously until a 
new nozzle has been inserted in place of the one 
which is now worn so much as to make it 
uneconomical in steam consumption. 

Provided that means are taken to prevent waste 
of steam due to worn nozzles, the steam jet con- 
veyor is very serviceable and, being flexible and 
convenient, it is very useful for the purpose for 
which it has been developed. 

The following estimated steam consumptions are 

* Inst. Mechanical Engineers Journal, March, 1920, 
p. 291. 



74 PNEUMATIC CONVEYING 

given for what they are worth ; they are of com- 
parative value in relation with the power con- 
sumption on the " suction " scheme : One firm 
claims, in an actual proposal for a plant to be 
erected in this country, a consumption of 30 Ibs. of 
steam per min. to deal with 150 Ibs. of ashes per 
min., or 4 tons per hr. This is approximately 
equivalent to 72 electrical h.p. for dealing with 
4 tons of ashes per hr. A second firm states that 
a steam- jet plant dealing with 12 tons per hr. will 
require 3,466 Ibs. of steam per hr. at 130 Ibs. 
pressure : this, if passed into a modern steam 
driven generator, would produce over 130 h.p. 
hours. These figures indicate how variable are 
the estimates of power required. Note. The 
" suction " schemes for wheat actually work out 
at slightly more than 1 h.p. per ton per hr. in 
single nozzle plants, and 1J h.p. per ton per hr. 
in twin nozzle plants. 

Lay-out of Plant. The plant is usually designed 
on the following lines : Immediately under the 
ash hoppers are funnel-shaped tee-pieces fitted to 
a cast iron pipe laid on the floor, or preferably in 
a small trench just below the ground level. These 
funnel inlets are usually covered with a cap when 
not in use, a tight joint being established by the 
" suction " in the pipe line. When used on 
Lancashire boilers having no ash basement the 
ashes are raked from under the furnaces on to the 
floor, and swept into the inlets mentioned (see 
Fig. 25). Large pieces of clinker are broken by 



76 PNEUMATIC CONVEYING 

hand until they enter the intake pipe, when they 
are immediately conveyed through the rest of 
the system. 

In all large boiler houses with a proper ash 
basement it is usual to have a travelling clinker 
breaker, motor driven, which can be moved on 
light rails under each ash hopper and over each 
intake. The breaker receives all the ashes when 
released by the hopper valve, crushes them 
to a suitable size and discharges them by 
gravity over the intake funnels, whence they are 
transported to the ash tank or hopper. 

The method of creating the moving air currents 
is by passing steam through specially designed 
nozzles which are placed at the extreme end of 
the intake pipe, and force the air out of the "pipe, 
thus inducing a stream of air to enter at the intake 
openings, and carry forward the ashes which have 
been fed into the pipe with the air. When the 
underground pipe has to rise vertically to cross 
roads, etc., or to reach an overhead tank, it is 
usually found necessary to insert " booster " jets 
to impart additional velocity to the ashes, which 
are naturally retarded seriously in changing their 
direction at the bend or elbow. Should circum- 
stances necessitate many bends being employed in 
the pipe line the number of " booster " jets has 
to be increased, and the total cost of steam for 
operation is increased seriously. 

The capacity of the conveyor depends upon the 
volume of air passed through the pipe in a given 
time, and the ashes must not be slacked before 



STEAM JET CONVEYORS 77 

handling, but must be handled either straight 
from the furnaces or allowed to cool and then 
conveyed to the ash hopper. 

An Sin. pipe is the largest used, and this will 
handle approximately 8 tons of ash per hour. Any 
increase over this size of pipe necessitates a 
consumption of steam which makes the scheme 
impracticable. 

The conveyor pipe may be run at any angle, 
elevation or level, and therefore is not handicapped 
by the rigid straight line, point-to-point, require- 
ments of bucket elevators, skips, etc. 

The abrasive action of ashes is well known, and 
when they are travelling at the high speed necessary 
with this form of conveyor they cause considerable 
wear at the bends and elbows in the pipe line. To 
overcome this a special mixture of iron has been 
obtained, which is extremely hard and wear- 
resisting. Steel is quite unsuitable and ordinary 
cast iron is too soft for these conditions. 

Steam Jets. The James Brady Foundry Co. 
(Chicago, U.S.A.) state, in their Bulletin on this 
subject, that the special steam jet elbows are 
usually placed at the top and bottom of a vertical 
riser. The jet of steam from the nozzle enters 
the elbow directly in front of, and parallel to, the 
face of a special wearing liner. This prevents 
or reduces the wear on the liners, as the jet protects 
the liners from the pounding action of the ash. 
A renewable sectional liner is provided of specially 
hard metal at all points in which the material 



78 PNEUMATIC CONVEYING 

makes actual contact with the pipe or fittings. 
These liners are interchangeable in all elbows, and 
each individual liner can be turned end for end 
when affected by wear. 

In cases where the length of horizontal run 
exceeds 125 ft. it is necessary to supplement the 
primary nozzles by " booster " steam jets to 
maintain the velocity of the air current. 

Buffer Boxes. At the discharge end of the pipe 
line it is necessary to insert a baffle or buffer box to 
take the impact of the ashes, and thus prevent 
wear on certain parts that are not designed to 
stand up to the destructive effects of the impact. 
The function of the box is to bring the ashes to 
rest, so that they may fall by gravity into the ash 
tank or on to the storage pile. When delivering 
into a tank it is very essential to install a buffer 
box, as otherwise the velocity with which the 
ashes enter the tank will pack them so tightly 
that they will not discharge automatically through 
the valve or gate. The location of the ash hopper 
can be wherever most convenient for loading the 
vans, railway trucks, or barges, etc., but preference 
should be given to a site which makes possible a 
pipe run with a minimum number of bends. 

One American firm of engineers, the Vacuum 
Ash and Soot Conveyor Co., New York, have done 
away with the numerous steam jets and the blowing 
effect produced thereby, and rely entirely on 
suction by using a sealed ash tank and exhausting 
the container and pipe system by means of a 



STEAM JET CONVEYORS 79 

single steam jet injector built into the roof of the 
ash tank, and discharging its steam directly into 
the air. 

By this means it is claimed that the following 
advantages are obtained : (1) No sand-blast effect, 
such as is inevitable when blowing at high velocity. 
(2) No steam enters the ash tank and consequently 
there are no condensation troubles. (3) Much less 
dust is blown into the atmosphere as the steam 
is never in contact with the dust. (4) Conveyor 
pipes are cleaner since no steam enters them, as 
in " blowing," and there is therefore no 
condensation, caking and corrosion. 



CHAPTER VIII 

MISCELLANEOUS APPLICATIONS OF PNEUMATIC 
CONVEYING 

Pneumatic Despatch Tubes. The ordinary pneu- 
matic conveyor picks up material at one point and 
unloads it at another and continues this course 
consistently, whereas the " pneumatic despatch 
tube " is a conveyor of small articles enclosed in 
a special cartridge which is built to fit the tube 
and which travels to and fro as required, carry- 
ing a variety of articles, or if necessary, the same 
articles, backwards and forwards between the 
same two stations or a series of fixed stations. 

The despatch tube thus constitutes an effective 
" mechanical messenger." One or more tubes are 
run between the points to be connected, with a 
despatch and receiving terminal at each end, or 
if necessary, a single line to operate in both 
directions can be designed. The tubes vary from 
1 J ins. to 4 ins. diameter, and they are also made 
of oval sections up to 4 ins. x 7 ins. ; rectangular 
tubes have been installed in special installations, 
chiefly in telephone exchanges for convenience 
in dealing with certain cards there employed. 

Tubes. The tubes are of lead and are usually 
encased for protection against mechanical damage, 

80 



MISCELLANEOUS APPLICATIONS 81 

and the erection is carried out with great care so 
as to preserve the smooth interior. Joints occur 
at intervals of 28 ft. or less, and are " wiped " 
with an ordinary plumber's joint over an internal 
mandril which is heated previous to insertion 
in the tube. Air-tight joints and smooth interiors 
are absolutely essential to a successful installation. 

Carriers. The carriers or cartridges in which the 
material to be transmitted is placed are made of 
gutta-percha covered at the ends with felt. One 
end of the container is closed and the other end 
is left open, but a " skirt " of felt surrounds the 
open end, and, as this is the " trailing " end and 
the air pressure is behind it, the air forces open the 
" skirt," making a tight fit and preventing leakage 
of air past the carrier. The nose of the carrier is 
usually fitted with a felt " buffer " which also 
assists in making an air-tight fit. A carrier for a 
2J in. tube is 6| ins. long and weighs empty about 
3 ozs. Fig. 26 shows a large carrier. 

Methods of Working. Pneumatic tubes are 
worked either by air above atmospheric pressure or 
by reducing the pressure below atmospheric. In 
the pressure system the usual pressure is about 
10 Ibs. per sq. in. above atmospheric pressure, 
whilst in the suction system the vacuum employed 
is equivalent to about 6J Ibs. per sq. in. 

Also, the method of working may be either 
" continuous " or " intermittent " ; in the first 
system the air, either above or below atmospheric 



MISCELLANEOUS APPLICATIONS 83 

pressure, is circulating continuously and the cart- 
ridge or carrier is inserted into a stream of air 
already in circulation, whilst in the " intermittent " 
system the power, either pressure or suction, is 
admitted to the conveyor tube only after the 
carrier has been inserted, and it is again cut off 
when the carrier reaches the end of its journey. 

To a great extent the success of a pneumatic 
tube system is the speed at which it can transmit 
the message sent by this means. In the " con- 
tinuous " system, working above atmospheric 
pressure, the speed is not so great as in the 
" intermittent " scheme, because the pressure in 
the tube is the same in front of and behind the 
carrier, which has to displace the air in front of it. 
In the " intermittent " system the pressure is 
turned on after the carrier is in place, and the 
advancing carrier has only to move the air at 
atmospheric pressure. On the other hand, if 
suction is employed, the " intermittent " system 
is slower than the " continuous " system because 
the air has to be exhausted to a certain point 
before the carrier begins to travel. It is true that 
it will begin to move as soon as the difference in 
pressure amounts to a few ounces, but there is a 
distinct " time lag " compared with inserting 
the cartridge into a tube continuously exhausted 
when it starts off at practically full pressure and 
speed immediately. 

The difference in time is stated by Kemp to be 
3 per cent, longer with " continuous " pressure, 
compared with " intermittent " pressure at 6 Ibs. 



84 PNEUMATIC CONVEYING 

per sq. in. ; the difference increasing to 6 per cent, 
when the pressure is raised to 14 Ibs. per sq. in. 
The average working speed of these tubes is from 
25 to 30 miles per hour. 

Power Required for Operation. It is difficult 
to determine the actual amount of power necessary 
to carry a cartridge through a tube. Kemp's 
Engineer's Year Boole states that, working at the 
standard pressure of 10 Ibs. per sq. in., the power 
required is theoretically 3 - 35 h.p. for a 2J in. tube, 
1 mile long, but actual experience suggests that 
at least 50 per cent, should be added to allow for 
losses from various causes, making the actual 
power, say, 5 h.p. per 2J in. tube per mile. 

Pressure receivers or tanks are inserted between 
the pump and the travelling tube to compensate 
for the impulses due to the irregularity of the 
pumps and also to act as reservoirs furnishing 
additional power during periods of abnormal 
working. 

The vacuum system takes less power (for a 
definite time of transmission) than is required 
by the pressure method of working, but local 
conditions always influence results considerably, 
and it is inadvisable to give any definite figure as 
to the power required, without actual knowledge 
of the system and conditions involved. 

The air compressors are usually driven electric- 
ally, but they can, of course, be operated by any 
other prime mover such as oil, gas, or steam 
engines. It is economical to combine the pressure 



MISCELLANEOUS APPLICATIONS 85 

and suction systems by arranging the air com- 
pressor to draw air from the vacuum receiver 
into the compressor cylinders whence it is returned 
to the pressure line. 

Automatic valves keep the pressures in the 
pressure and vacuum sides of the system within 
pre-determined limits. " Make up " air is ad- 
mitted by the automatic opening of an atmospheric 
valve when the pressure side of the system is 
low and the vacuum side high, so that the pump 
is deprived of sufficient air to operate the system 
efficiently. Should the conditions become reversed, 
that is, a low vacuum and a high pressure, then 
the pump is working against a high back pressure, 
and this is reduced by the opening of an atmos- 
pheric relief valve which remains open until the 
vacuum is restored to normal pressure. This 
system is preferable to and more economical than 
the use of two separate pumping and exhausting 
machines. 

Elaborate and valuable tables of horse-power 
required by compressors and of " transit times " 
for distances up to 4,500 yds. with 1 \ in., 2J in., 
and 3 in. tubes are given in Kemp's Engineer's 
Year Boole. 

The Lamson Tube Co., Ltd., have brought what 
was originally invented as a means of conveying 
persons to a practical business accessory, capable 
of saving a great amount of time by despatching 
sketches, papers, small articles, money, etc., here, 
there, and everywhere at the rate of 30 miles an 
hour. 

7 {5362 ) 



86 PNEUMATIC CONVEYING 

The utility of these plants has long been recog- 
nised by banking establishments, the General Post 
Office, large stores, factories, newspaper publishing 
offices, etc. (see Figs. 27 and 28). 

In addition to the conveyance of messages and 
papers, they are frequently installed to convey 
money and bills from the numerous departments 
of a large store to the cashiers, thus saving time 
and effecting economy in labour and floor space. 
One cashier can attend to from 10 to 15 stations, 
or in small establishments all the stations can be 
centralized around the book-keeper. 

The installation of a power-driven plant is not 
essential, providing that the service required is 
not too great. A foot power pneumatic service is 
available and it is in use in many business 
establishments. In this system the methods of 
transportation are similar to those in a power 
plant, but the tubes are brought to a special 
cabinet 15 ins. square by 2ft. 6 ins. high, in which 
is mounted a foot-operated pump of patented 
design without bellows or cords. The pump is 
operated as and when the service is required, and 
there is no loss of any description when the 
apparatus is not in use. 

Pneumatic Tubes for Heavy Articles. It is 

interesting to recall, especially in view of the 
proposed use of pneumatically-propelled parcel- 
conveying trains by the G.P.O. in London, the 
proposal made by Mr. Medhurst, in 1810, when it 
was suggested that a carriage somewhat similar 




FIG. 27. TUBE CENTRAL IN WHOLESALE DRUG 

HOUSE, DISTRIBUTING ORDERS TO ALL 

DEPARTMENTS. 




FIG. 28. LAMSON DISTRIBUTING STATION IN 
WELL-KNOWN PUBLISHING HOUSE. 



MISCELLANEOUS APPLICATIONS S9 

to the modern railway carriage should be moved 
through a tunnel by pneumatic means. So long 
ago as 1667, Denin Papin read before the Royal 
Society a paper entitled " A Double Pneumatic 
Pump," and definite mention of despatch tubes 
was made in this paper. 

In 1840 a pneumatic railway was actually built 
and worked between London and Croydon, and 
in view of its success was followed by others 
between Dalkey and Kingstown and between 
Exeter and Plymouth. From this it will be seen 
that transportation by pneumatic means is not 
modern in its application, and was originally 
intended for very large tubes and weights, but 
modern development has been toward small tubes 
and light weights. 

The Vacuum Cleaner. The pneumatic trans- 
porting of material in the form of dust has been 
brought to a very high state of perfection during 
recent years and an enormous number of plants 
is now in use, ranging from the hand-propelled 
machine to very large stationary equipments. 

Certain hand-propelled machines have been 
constructed in such a way that the fan is directly 
operated by gearing from the running wheels, and 
after a few moments a very considerable speed is 
attained and the suction of the fan is used for 
lifting the dust from the surface over which the 
apparatus is travelling. 

Numerous designs of more powerful machines 
actuated by hand bellows have been placed on the 



90 PNEUMATIC CONVEYING 

market and these possess the advantage that they 
are independent of the use of power ; but it is not 
altogether easy to operate a machine by one hand 
and to manipulate the nozzle with the other. 

Electrically-driven machines of almost number- 
less designs are available. These usually employ 
a high-speed fan of the single-stage type, but a 
piston pump is embodied in some designs. 

In the removal of dust the same principle 
applies as in the conveying of heavier materials, 
i.e. it is not so imperative to obtain a high vacuum 
as it is to have a large volume of air moving at 
high velocity, hence the multi-stage turbine 
machine has distinct advantages as regards weight 
of material moved and economy of power. 

The multi-stage exhauster consists of turbine 
wheels mounted on a single shaft, the air being 
drawn into the first wheel, from this to the second 
wheel and so on right through the machine, each 
wheel increasing the suction on the intake end 
according to the total number of wheels or stages. 
This style of machine is procurable in either the 
stationary or portable type, and in both it is made 
in various sizes, the portable machines ranging 
from yV h.p. up to J h.p. for domestic purposes, and 
from 1J to 3 h.p. on trucks for cleaning electrical 
machinery, railway carriages, etc. Figs. 29 and 
30 illustrate typical stationary and portable plants 
respectively. 

It is not generally recognized what enormous 
amounts of dust and dirt may be extracted by 
these machines. From one London hotel a \ h.p. 




FIG. 29. STATIONARY TURBO-EXHAUSTER WITH 
DUST SEPARATOR. 




FIG. 30. PORTABLE TURBO-EXHAUSTER DRIVEN BY 
1 H.P. B.C. MOTOR. 



92 PNEUMATIC CONVEYING 

cleaner removed 166 Ibs. of dust from the carpets of 
the public rooms only. On a cleaning test in a 
first class dining car on one of the English railways 
25 Ibs. of dust was removed from 38 sq. yds. of 
carpet. A rug in front of a lift in a London 
stores yielded 91 Ibs. 1 oz. of dirt to a small 
machine. 

The stationary plants are usually installed in the 
basements of large office buildings, theatres, hotels, 
clubs, etc., and the whole building is piped suitably, 
wall plugs or connectors being fitted to which the 
staff make connection by flexible hose as and when 
required. The free end of the flexible hose is 
fitted with one or other of a series of special nozzles, 
the latter being adapted to the varying require- 
ments of everything in the room from floor to 
ceiling. 

With the portable hand sets or even with the 
larger truck type, the design is complete as a 
working unit ; the equipment is used as manu- 
factured and there is little or no chance for the 
user to endanger the working efficiency of the 
plant. In permanent plants, however, as installed 
in hotels, etc., it is necessary that all points 
previously mentioned regarding pipe lines, valves, 
junctions, bends, etc., should be considered and 
acted upon. 

The pipe lines should be too large rather than 
restricted in any way, the suction flexible should be 
kept as short as possible, and if necessary extra 
connections should be allowed rather than require 
flexibles too long for use without " kinking." 




FIG. 31. SUCTION CLEANING FOR RAILWAY 
CARRIAGE CUSHIONS. 




FIG. 32. STURTEVANT EQUIPMENT FOR OFFICE 
CLEANING. 



94 PNEUMATIC CONVEYING 

Fig. 31 illustrates a stationary suction cleaning 
plant applied to cleaning railway carriage cushions, 
and Fig. 32 shows a similar installation in use in 
an office building. 

Cleaning by Air Blast. By transferring the hose 
from the suction side to the discharge, a suction 
cleaner may be used to blow dust from machinery 
of all kinds and from places that are high up and 
cannot be cleaned economically by suction. For 
cleaning electric generators and motors by blast, 
these machines have many advantages, and on 
account of the large volume of air handled they 
are much to be preferred to the small- volume 
high-pressure jet of the ordinary air compressor 
often used for this purpose. With the portable 
turbo-blower there is no danger of damage to the 
insulation through high pressure, or through the 
carrying of moisture and oil into the windings 
with the air jet. 

Pumping by Compressed Air. Although, gener- 
ally speaking, the raising of water by compressed 
air is not an economical method, it is frequently 
adopted in mining and tunnelling where the use 
of steam or electricity is objectionable. In these 
cases, cost of operation is a minor factor, and it 
may be interesting to give a few particulars of 
this form of pneumatic conveying. 

The simplest form of compressed air pump 
consists of a closed chamber or tank immersed 
in the water, to be raised or fixed at such a level 



MISCELLANEOUS APPLICATIONS 95 

that the water will flow into the tank. An air 
pipe is connected to the top of the chamber, and 
the rising main is carried inside the tank to the 
bottom. On opening the air valve, pressure is 
exerted on the surface of the water in the tank, 
and the water is expelled through the lift pipe or 
rising main. On closing the air valve, water 
again fills up the tank, and the process is 
repeated. 

A decided improvement on this pump is the 
return air pump, which consists of two closed 
chambers connected through valves with the 
rising main. The compressed air pipe passes 
through a two-way valve, either into one tank or 
the other, this valve being positively operated. 
The method of working is similar to that of the 
single acting pump, considering each chamber 
separately, but one tank is filling while the other 
is being emptied. 

The air expelled from the filling tank, instead 
of being discharged to atmosphere, and part of its 
expansive power lost, is carried back through the 
pipe, which would be the air intake pipe when 
discharging, through a port in the two-way valve, 
and into the compressor intake pipe. The air 
leaving the filling tank is naturally above atmos- 
pheric pressure, and assists the piston on entering 
the compressor, thus reducing the power absorbed 
in driving the latter. 

Air-lift Pumping. The air-lift pump is a 
common means of conveying by pneumatic means 



96 PNEUMATIC CONVEYING 

and should not be confused with the above methods 
of raising water by compressed air. 

In the air-lift method of pumping air under 
pressure is admitted at the foot of a pipe already 
submerged in the well. The air does not merely 
bubble through the water, as might be supposed, 
but passes up the pipe as a mixture of air and 
water. The introduction of the air into the rising 
column of water makes the latter as a whole less 
dense than the water around the tube, and there- 
fore we have a difference in head between the 
internal and external columns of water which will 
carry the internal column considerably higher than 
the external column. 

As the lifting force depends upon the " head " 
of water outside the rising main, it follows that the 
maximum height to which the water can be raised 
depends upon the depth to which the air pipe 
and rising main are submerged below the standing 
level of the water in the bore-hole. In other 
words, the greater the lift, the greater the depth 
to which the air pipe must be carried before 
releasing the air into the rising main. 

Experience shows that the water pipe should be 
submerged 18 ins. for every 1 ft. lift above the 
water level in the bore-hole, and allowance must 
be made for the " depression " of the water 
level in the bore-hole, which will probably take 
place when pumping is in progress. This depres- 
sion will vary according to the water bearing 
capacity of the strata, in which the hole has been 
bored, hence it is necessary to go carefully into 



MISCELLANEOUS APPLICATIONS 97 

the conditions before boring the hole. If available, 
data should be studied concerning the standing 
water level, and the pumping depression in other 
bore-holes in the immediate neighbourhood. Also 
tests should be made before the boring machinery 
is removed because, although the initial depth of 
bore-hole may be satisfactory on the basis of 
standing level calculations, it may be found that 
when pumping the depression is so great that 
the bore-hole has to be carried to a greater 
depth. 

The air is supplied at a pressure suitable for the 
conditions, and can be carried down a separate 
tube and connected to the rising main at the correct 
depth (Fig. 33), or, as is often done, one pipe may 
be lowered and the rising main supported centrally 
inside the casing tube, the annular space between 
the two being used as the air pipe (see Fig. 34). 

The amount of free air required is from O6 to 
TO cu. ft. per gallon of water raised per ruin., 
provided that all the details have been studied 
carefully and the design of the plant worked out 
accordingly. 

If the air pipe is too small the air will bubble 
slowly through the water, while if it is too large it 
will blow out with great force, spraying and 
losing the water : the ratio between the cross- 
sectional area of the air and water pipes is about 
1 J to 4. 

Advantages of air-lift pumping are that a greater 
amount of water can be obtained from a hole of 
given size than by ordinary pumping ; and that 




Mixture of 
Air and Water. 




AIR-LIFT PUMPING 



FIG. 33. AIR PIPE 
OUTSIDE RISER. 



FIG. 34. AIR BETWEEN 
CASINO ANP RISER. 



MISCELLANEOUS APPLICATIONS 99 

one compressing plant can deal with several wells 
instead of needing a separate pump to each well. 

The disadyantages are, that the mechanical 
efficiency is low ; that a considerable amount of 
air is entrained in the water, and aerated water 
is very unsuitable for boiler feed purposes ; and 
that means must be provided to allow air to 
escape by passing the discharge from the pump 
over a weir or similar contrivance. It is necessary 
to have some reliable form of oil trap between the 
compressor and the well to prevent contamination 
of the water by oil carried over by the air from the 
cylinders of the compressor ; this is difficult, 
because the oil is not only " atomized " but is 
actually vaporized while in the compressor cylin- 
ders and as a gas it is difficult to reclaim. The 
air must be kept as low in temperature as possible, 
and it is usually passed through a cooler before 
being delivered down the well. 

At times, air-lifts are installed for conveying 
other liquids to a height, and when these can be 
treated at a high temperature it is advisable, as 
the efficiency is then much improved. Even under 
these conditions it is advisable to cool the air to 
the lowest feasible temperature, before using it 
as a lifting medium. 

When starting up, the column of water in the 
rising main has to be moved as a solid column, 
and consequently a higher pressure of air is required 
at starting than when the column has been set 
in motion, as the water and air then pass up in 
alternative " pellets." 



100 PNEUMATIC CONVEYING 

In chemical works and allied industries this 
pneumatic method is frequently used for pumping 
acids, and other corrosive liquids from one place 
to another. Compressed air is a very handy 
medium for this class of work as ordinary mechani- 
cal methods are ruled out, due to the impossibility 
of introducing corrosive liquids into the pumps and 
syphons unless great expense is incurred by the 
use of acid-proof materials. 

The air lift is also very advantageous for pumping 
water which contains a large amount of sand or 
similar gritty material which would cut and score 
the walls of an ordinary piston pump. Air-lift 
pumping is frequently used, therefore, on new 
bore-holes until the sand, etc., has been eliminated, 
after which the final pump can be installed without 
fear of damage. 

The question of submergence will frequently 
make it impossible to use air lift without boring 
many feet deeper than would otherwise be 
necessary, but when the water bearing strata 
is low this form of pumping is frequently very 
convenient. 

Miscellaneous Applications of Pneumatic 
Conveying. Several other interesting applications 
of pneumatic conveying may be enumerated but, 
being somewhat outside the primary scope of this 
book, they will not be discussed in detail. The 
main object of the author is to raise interest in 
the handling of solid materials in a manner 
practically unknown to the general reader. 



MISCKLLANEOUS APPLICATIONS 101 

The housing problem has developed the pneu- 
matic handling of cement in a liquid form, and houses 
are now being built of reinforced cement in the 
following manner. An expanded steel frame is 
supported between concrete or brick piers, and on 
wood sheeting where necessary, and liquid cement 
is blown on to the metal in the form of a liquid 
spray : the first coat dries quickly and leaves a 
certain amount of cement covering the framework. 
Then follows another coat, and again another and 
so on, until the whole of the framework has been 
covered to an appreciable thickness. The result 
is a thin wall or slab of cement reinforced with the 
steel and of great combined strength. Slightly 
domed roofs constructed in this manner have 
proved very strong and durable. 

The Aerograph is an instrument working on the 
same principle for the application of paint, and 
it is used a great deal in the art world, in the 
manufacture of Christmas cards, in panel painting, 
and in interior decoration generally. Excellent 
" tones " and shades are obtained by the simple 
method of varying the thickness of the colour or 
the number of coats applied. It is usual to convey 
the surplus colour and fumes away from the 
operator by means of a stream of air through a 
special hood placed at the back of the work, thus 
maintaining clean pure air for the operator. 

A similar machine of more crude design is used 
for whitewashing walls of stables, cattle pens, etc. 
All these plants comprise an air compressor, 
either power or hand operated, from which the 

8 (5362) 



102 PNEUMATIC CONVEYING 

air is led to a special injector which draws up 
through a second pipe a certain amount of the 
material to be sprayed. The paint or other 
material is then atomized and impelled with 
considerable force on to the surface to be covered. 

The sand blast is another application of pneu- 
matic conveying in which the medium conveyed 
is sand, which has well-known cutting and erosive 
effects when it impinges on a surface at high 
velocity. This plant is used for decorating glass- 
ware, obscuring sheet glass, and also for cleaning 
stone buildings by the actual removal of the face 
of the previously discoloured stone. 

The pneumatic conveyance of energy is exemplified 
by rock drills, riveting machines, coal-cutters and 
innumerable other portable tools. Energy is 
expended in compressing air which is transmitted 
through pipes and made to yield its stored energy 
by driving the air motors of the tools or other 
apparatus in question. 

Conclusion. Enough has been said to show that 
pneumatic conveying has made great progress, and 
that the possibilities of this method of dealing 
with the moving of solid materials are much 
greater than has been generally recognized. 

Almost anything that will enter a pipe up to 
about 9 ins. diameter can be conveyed in this way, 
either by " blowing " or " suction " or by the 
" induction " method. 

Weight and size is an advantage rather than 
otherwise, and bricks can be dealt with more 



MISCELLANEOUS APPLICATIONS 103 

successfully than flour. The writer's experience, 
in the results of actual working with pneumatic 
conveying, indicates that no problem should be 
considered too difficult to be tackled by this 
method, and that even the most unlikely materials 
can be conveyed successfully by pneumatic means. 



BIBLIOGRAPHY 

READERS wishing to amplify their knowledge of pneumatic 
conveying may find useful the following references 

" Pneumatic Dispatch," by H. R. Kemp, M.I.C.E., 
M.I.E.E., M.R.M. Paper before the Inst. of Post Office 
Engineers. October, 1909. 

" Power Plant for Pneumatic Tubes in the Post Office," 
by A. B. Eason, M.A., A.M.I.E.E. Paper before the Inst. 
of Post Office Engineers. 18th October, 1913. 

" Portable Plant." Editorial article in Gassier' 8 
Engineering Monthly, June, 1919. 

" Pneumatic Handling Machinery." Engineering and 
Industrial Management, 5th June, 1919. 

" History of Conveying," by G. F. Zimmer, A.M.I.C.E. 
Engineering and Industrial Management, July to Sept., 
1920. 

" Boots as Power Users," by E. G. Phillips, M.I.E.E., 
A.M.I.Mech.E., describing the coal handling plant used 
by Messrs. Boots Pure Drug Co., Ltd., Nottingham. 
Power User, March, 1920. 

" Pneumatic Handling Installation for Calcium Sul- 
phide," by G. F. Zimmer, A.M.I.C.E. Chemical Age, 
10th April, 1920. 

" Pneumatic Conveying of Granular Substances, 
including Chemicals," by G. S. Layton. Paper before 
the Society of Chemical Industry, Third Conference 
(Birmingham), 23rd April, 1920. 

" Pneumatic Conveying of Coal and Similar Substances," 
by J. H. King, M.I.Mech.E. Paper before the Society 
of Chemical Industry, Third Conference (Birmingham), 
23rd April, 1920. 

Instructive catalogues on this and allied subjects are 
issued by the following firms (amongst others) : Messrs. 
Ash well & Nesbit, Ltd., Leicester ; R. Boby, Ltd., Bury 
St. Edmunds ; H. J. King & Co., Nailsworth, Gloucester ; 
The Lamson Store Pneumatic Co., Ltd., London ; and 
The Sturtevant Engineering Co., Ltd., London. 



105 



INDEX 



ADVANTAGES of system, 5 

Aerograph, 101 

Air compressors, 67, 70, 71 

filters, 10, 21-27 

induction, 63 

- lift, advantages, 97 

, air required, 97 

"depression," 96 

pumping, 95-100 
submergence, 96, 



100 



receivers 69 
reheating, 68, 69 
velocity, 36 

<i 



" Aquadag," 20 

Ash handling, 58, 74-77 

BAG filters, 22-24 

Bends and elbows, 34, 35, 67 

Bibliography, 105 

" Blowing " system, 4 

Breaking of materials, 34, 35, 

67 
Buffer boxes, 78 

CAPACITY of pipe lines, 36 
Cement handling plants, 101 
Cleaning with air blast, 94 
Coal -handling plants, 54-58, 

60, 61 

Comparative costs, 53 
Conveying above atmospheric 

pressure, 6 

below atmospheric pres- 
sure, 6 

above and below atmo- 
spheric pressure, 6, 64-66 

Cyclone separators, 21 

DESIGN, factors influencing, 8 
Despatch tubes, 80, 81 
Dischargers design, 10, 28-32, 
56, 57 

difficulties, 9 

valves, 28, 31, 32, 56, 58 



EXHAUSTERS, 10, 14 

FACTORS influencing design, 8 

Flexibility, 5 

' Flexible suction pipes, 36 
I Floating plants, 3, 46, 51, 59- 

61 
I Flue cleaning, 59 

Foot -power pumps, 86 

Fundamental principles, 3 

GRAIN handling, 45, 47 

HEAVY commercial systems, 7 
High-pressure systems, 6, 39 
Historical, 1, 2 

" INDUCTION " system, 4, 6, 

62-66 
"Intermittent" tube system, 

81, 83 

JUNCTIONS in pipe lines, 33 

KING'S exhauster, 10-14 
three-way valve, 37 
" Kinking" to be avoided, 92 

LARGE pipe systems, 7 
Lime washing, 101 
Low-pressure systems, 6 
Lubrication, 20 

MATERIALS, breaking of, 34, 

35, 67 
Mollers' air filter, 24 

NASH hydro -turbine, 18, 19 
Nozzles (suction), 10, 40-43 

OIL contamination, 11 



PIPE lines, 10, 33, 36, 39 
, capacity of, 36 



107 



108 



INDEX 



Pneumatic tube carriers, 81, 
82 

-, " continuous," 81, 



83 

83 
85 
85 



- foot power, 86 

-, "intermittent," 81, 

-, power required, 84, 

- pressure system, 81, 
vacuum system, 84 



Portable quayside plant, 5 

railway plant, 49-51 

vacuum cleaners, 92 

Power required, 44 
Pressure systems, 4, 6 
Pumping by compressed air, 
94, 95 

QUAYSIDE plants, 51 

REHEATING compressed air, 68, 

69 
Rotary blowers, 14, 15 



SAND blasting, 102 
Stationary plants, vacuum, 92 
Steam consumption, 72-74 

jet conveyors, 72, 74, 76 

jets, 77 

jets, economy of, 72, 73 

Sturtevant blowers, 16, 17 
"Suction" nozzles, 10, 40-43 

systems, 4-7 

Systems, advantages of, 5 

TELESCOPIC pipes, 38 
Turbo-blowers, 11 

VACUUM cleaners, 89 
, tests, 92 

required, 3 

Valves in pipe line, 37 
Velocity of air in pipes, 36 

WATER pumping, 95-100 
Waterside plants, 45, 47, 48, 

59 

Wear of pipes and bends, 34, 35 
Wet air niters, 25-27 



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