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UC-NRLF
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ondensers
From
Power
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s
LIBRARY
HKiymSJJY OF CALIFORNIA
PaVis
CONDENSERS.
A series of Lectures and Articles upon the Subject
reprinted from the columns of
NEW YORK:
The Power Publishing Company,
World Building.
1901.
LIBRARY
UNIVERSITY OF CALIFORNIA
DAVIS
Entered accotding to act of Congress, in the year 1900, by The Power Publishing
Company, in the office of the Librarian of Congress at Washington.
LECTURE VIII.— CONDENSERS.
BY F. R. LOW.
If you build up a solid column of bricks the pressure which it
exerts on its base will increase directly as the height of the col-
umn. A column ten feet in height will press twice as hard on
its base as a column five feet high, and a column ioo feet high
ten times as hard as a io-foot column.
Now, the point I want to make is that the pressure per square
inch of base depends altogether on the height and not on the
width or diameter of the column. A column 2 feet square will,
it is true, press on its base with four times the pressure of a col-
umn one foot square and of the same height, because there are
four times as many bricks in it and it weighs four times as much,
but there is also four times as much base to it, so that the pres-
sure per square inch of base is entirely independent of the cross
section and depends upon the height alone.
The same thing is true of water. A cubic foot of fresh water
weighs 62.355 pounds at 62 degrees Fahrenheit. It is easy to
remember this weight approximately, for it is the same as the de-
grees and 62 is a standard temperature in dealing with water. A
cubic foot rests on a base of 144 square inches and is a foot high,
so that the pressure per square inch on the base would be
62.355 ~r-T44 — °-433 of a pound
and for every foot in height that we build our column or fill our
pipe with water we gain 0.433 °f a pound pressure per square
inch. If one foot or 12 inches gives us 0.433 of a pound it would
take a column
12 -— .433 = 27.71 inches
in height to exert a pressure of- one pound per square inch. For
Fluid Pressure is Dependent upon Height of Column.
every 27.71 inches in vertical height between the point at which
you are measuring and the top of a column of still water there wilt
be a pressure of a pound to the square inch, and it makes no dif-
ference whether you are measuring the pressure at the bottom of
a one- eighth inch pipe, a twenty foot stand-pipe, or a lake, or the
ocean itself. Every once in a while we have to explain this to-
the man who believes it takes more power to feed into the bot-
tom of a tank than into the top, on account of the weight of
water in the tank. The bottom of the tank holds up all the
water except the column directly over the opening of the deliv-
ery pipe, so that the additional pressure on the pump is due only
to the depth of water in the tank, not to the size of the body,
and it is impossible to feed into the top without increasing the
height of the column fully as much. It makes no difference
whether the height is due
to the depth of the water
inside the tank or an ad-
ditional length of pipe
outside. The difference
between the water and
the column of bricks is
that while the pressure
of the latter can act only
vertically that of the
water can act in all di-
rections so that as you
lower a body into the water the pressure upon its surface in all
directions increases one pound per square inch for every 27.71
inches of depth of water above it. In Fig. 1, for instance, the
pressure due to the column of water P will act upward upon the
piston A and sidewise upon the pistons B and G as well as down-
ward upon the piston D.
We live at the bottom of an ocean of air. The winds are its
currents, we can heat it, cool it, breathe and handle it, weigh it,
and pump it as we would water. The depth of this atmospheric
ocean cannot be determined as positively as could one of liquid,
for the air is elastic and expands as the pressure decreases in the
upper layers. It is variously estimated at from 30 to 212 miles.
We can, however, determine very simply how much pressure it
exerts per square inch.
^1
r
P
/
1
:
=fe=
;-
z^^s.
B
; — ; ' p
—~^== =
Fi
9-
EfT^
Measuring the Pressure of the Atmosphere.
Here is a U-tube, Fig. 2, into which a quantity of mercury
"has been poured. It stands at an equal height in both legs. Into
one leg I pour some water on top of the mercury, and the mer-
cury is depressed in that leg, and rises in the other. ^
The difference in level of the mercury is a meas-
ure of the weight or downward pressure of the
water.
The mercury below the line A B balances in
lx>th legs and the mass of mercury above that
line in the right leg just balances the weight or
pressure of the water in the other. The pressure
of the atmosphere makes no difference in this ex-
periment, for it is exerted on both columns equal-
ly. Now we can find the pressure of the atmos- Fig. 2.
phere in a similar way by making it act on one
end of the mercury column as does the water here and keeping it
away from the other.
Here is a glass tube about a yard in length and filled with mer-
cury. Closing one end
with my thumb to pre-
vent a premature escape,
I invert it in a bowl of
mercury as in Fig. 3.
This is handier than the
U-tube but the principle
is the same. The bowl
is in effect the other leg
of the tube and no mat-
ter what its size may be
the atmosphere exerts a
certain pressure on each
square inch of its surface,
except at the point
covered by the tube,
and here the mercury
rises until it forms a
column high enough to
exert the same pressure
per square inch, so that the height of the column is a measure
4 Nature and Measurement of a Vacuum.
of the atmospheric pressure. This column will be approximate-
ly 30 inches, and as a cubic inch of mercury weighs about a
half a pound, each two inches of height will be equal to a pound
pressure, so that the pressure exerted by the atmosphere is about
1 5 pounds per square inch. This pressure depends first upon the
nature of the atmosphere. You know that steam or aqueous
vapor is lighter than air at the same pressure, so the more moist-
ure there is in the air the lighter the column of atmosphere
above us, and the less the height to which our column of mer-
cury will rise to balance it. Also the warmer the air becomes
the lighter it is. Again, if we carry our apparatus to the top
of a high mountain we shall find a considerable difference in the
height of the column, because we have lessened the height of
the column of air above us. This arrangement, which is
known as a "barometer," is therefore of use in indicating coming
changes in the weather, and elevations above the sea level, at
which our experiment is supposed to have been made.
We are then subjected all the time to a pressure of 15 pounds
to the square inch all over our bodies, yet we suffer no inconven-
ience, in fact, it took mankind a long while to find it out, be-
cause the pressure is the same in all directions, it is exerted in-
side as well as out, and there is no unbalanced pressure. It is
only when the atmospheric pressure is removed from one side and
allowed to act upon another that we get any effect. In a space
from which the air has been removed without allowing anything
else to enter, a "vacuum" is said to exist, and the vacuum is
more or less complete according to the more or less complete re-
moval of the air. In the space A in Fig. 3, exists the most per-
fect vacuum we are able to create, for the mercury in receding
has left nothing behind it, except possibly a little mercurial va-
por if there have been no air bubbles and no moisture between
the mercury and the glass. With this complete vacuum above it
the mercury will rise about 30 inches, and we would say that we
had "30 inches of vacuum." What we mean is that the pressure
has been so completely removed from the space A that the at-
mospheric pressure is able to support 30 inches of mercury
against the pressure that is left. Suppose we let a little air into
A. The mercury would fall more or less according to the amount
of air admitted, because this air would exert some pressure, there
Nature and Measurement of a Vacuum. 5
would be less difference between the pressure in A and that of
the atmosphere, and the atmosphere would be able to support a
lesser column against this greater pressure. If the column now
was 18 inches high we would say that we had 18 inches of vac-
uum, and should mean that the atmospheric pressure could sup-
port 18 inches oi mercury against the pressure in our vacuum.
These are the "inches" of vacuum upon the ordinary vacuum
gage. When the pointer stands at 26 inches it means that there
is difference enough between the pressure in the condenser and
that of the atmosphere to support a column of mercury 26 inches
high. If with an absolute vacuum the barometer stood at 30
inches, and if a cubic inch of mercury weighed half a pound the
atmospheric pressure would be 15 pounds, and two inches would
equal one pound. As a matter of fact the height of the barome-
ter varies and mercury weighs only .49 of a pound to the cubic
inch, so that the atmospheric pressure is nearer 14.7 than 15
pounds. When you put your hand over an opening into a space
containing a vacuum you feel it drawn to and held down very
hard upon the opening. This is due not to any attractive power
of the vacuum, but to the pressure of the atmosphere upon the
back of your hand unbalanced by an equal pressure on the area
in contact with the opening to the vacuum.
Here is an implement which every schoolboy knows under the
name of a "sucker," a circular pad of leather, thick, but pliable,
with a string through its center. It has been soaking in water.
I press it against the smooth wooden seat of this chair and am
able, you see, to lift the chair with a string. The boys used to
get themselves into disrepute with the householders in the vicin-
ity of the school by pulling the bricks out of the sidewalk in this
way. This action is not due to any attractive or adhesive prop-
erty of the leather, but to the fact that there is a pressure of
about 15 pounds per square inch pushing the leather against the
chair, and the atmosphere owing to the more or less complete
contact of the wet leather with the surface on which it rests can-
not get to the under surface to balance it. The disk is four
inches in diameter, having an area of 12.5 square inches, and the
atmosphere exerts a pressure on its surface of 14.7 X I2- 5 =
183.75 pounds with which the "sucker" would resist separation
from the surface to which it was attached, if the pressure was
How Water is Lifted by Means of a Vacuum.
entirely removed from its under-side, and other surface, and the
leather perfectly air tight.
We are accustomed to say that water is ' 'sucked up' ' or ' 'drawn
up" by a pump as though there was some pulling property to the
vacuum which it creates, when as a fact the water is pushed up
by the atmospheric pres-
sure acting on the sur-
face of the water in the
well. If in Fig. 3, we
had a tube of water in-
stead o f mercury w e
should find that the
water would rise in it
about 34 feet instead of
30 inches. We have
seen that it takes a col-
umn of water 27 71 in-
ches high to exert a
pressure of one pound,
then the atmospheric
pressure of 14.7 pounds
could support a column
of
2771 X r4.7=33 94 ft
12
In Fig. 4, we have a
steam pump drawing
water from a well.
Steam acting on the pis-
ton A pushes the piston
B toward the left, forcing
the water before it
through the upper valve
to the discharge pipe and leaving behind it a more or less complete
vacuum in the space C. Connected to the space C through the
lower valves is the pipe P, the lower end of which is immersed in
the water of the well. Here we have a reproduction (Fig. 4) of
Fig. 3. The well is the bowl, the pipe P is the glass tube, the
vacuous space C corresponds with the vacuous space A. There
Limitations of Lift.
is this difference, however, the pipe P is not so long but that the
atmospheric pressure can force the water clear through it, through
the valve into the cylinder C, ready to be forced out again when
the piston moves in the other direction. The difference in pres-
sure between the cylinder and the atmosphere must be sufficient
to lift the water from the level in the well to the level of the
pump cylinder, to lift the valve and to induce a flow sufficiently
to keep the cylinder full behind the receding piston, and these
considerations limit the distance that we can place a pump above
its source of supply, in other words its "lift." In the first place
we cannot get a perfect vacuum in contact with water. You re-
member that the boiling point of water de-
pends upon the pressure. In a boiler with
a pressure of 60 pounds by the gage, the
water will not boil until it is over 3000.
Under the pressure of the atmosphere it
boils at 2120, and as you reduce the pres-
sure below that of the atmosphere the boil-
3 ing point lowers rapidly. You can even boil
water at 32 ° if you reduce the pressure
power.y.r. sufficiently. In the table on page 8 are
Fl£- 5- shown the relations of pressure and tempera-
ture for water at from 32 ° to 2120. This means that if we had
an arrangement like Fig. 5, starting with a complete vacuum in
chamber A the mercury in the tube would not rise above the level
in the cup because there is a complete vacuum both in A and B.
Now if water of 32 ° be introduced into A it would boil and give off
vapor until the pressure in A arose to .089 of a pound, and the
mercury would rise in B 181 thousandths of an inch. A complete
vacuum as given by this table is 14.7 pounds, or 29.922 inches,
but the introduction of the water even at 32 ° has reduced the
vacuum to 29.922 — .181=29.741 inches. The heat necessary to
convert the water into vapor, which you will remember from an
earlier lecture was considerable in amount and was called the latent
heat, coming from the water and its surroundings, the water would
be frozen, and I have seen ice made by simply spraying water into
a space in which a high degree of vacuum was maintained. If
the water was 6o° the vacuum would be impaired .571 of an inch
or . 254 of a pound. This is the reason it is so difficult to pump hot
Temperature of Steam Below Atmospheric Pressure.
water. If the water in Fig 4 was 1500 the space Cleft by the
piston, instead of being a nearly complete vacuum, would be filled
with steam of 3. 708 pounds pressure, leaving only 14. 700 — 3. 708=
Pressure.
Vacuum.
Temperature
Inches of
Lbs. per
Inches of
Lbs. per
mercury.
square inch.
mercury.
square inch
Fahrenheit.
Inches.
•
32°
.181
.089
29 741
14.611
35°
.204
.100
29 718
14 600
40°
.248
.122
29 674
14.578
45°
.299
.147
29.623
14.553
50°
.362
.178
29.560
14 522
55°
.426
.214
29.496
14.486
60°
.517
.254
29.405
14 446
65°
.619
.304
29 303
14.396
70°
.733
.360
29,189
14 340
75°
.869
.427
29.053
14.273
80°
1024
.503
28.898
14 197
85°
1205
.592
28 717
14 108
90°
1.4L0
.693
28.512
14 007
95°
1.647
.809
28.275
13.891
100°
1917
.942
28.005
13.758
105°
2.229
1.095
27.693
13 605
110°
2 579
1.267
27 343
13 433
115°
2 976
1.462
26 846
13.238
120°
3.430
1685
26 492
13,015
125°
3.933
1932
25 989
12.768
130°
4 509
2 215
25.413
12.485
135°
5.174
2 542
24.748
12.158
140°
5.860
2 879
24.062
11.821
145°
6 662
3 273
23.262
11.427
150°
7 548
3 708
22.374
10 992
155°
8.535
4 193
21.387
10 507
160°
9.630
4.731
20.292
9.969
165°
10 843
5 327
19.079
9.373
•170°
12.183
5 985
17.739
8 715
175°
13.654
6 708
16.268
7 992
180°
15.291
7 511
14.631
7 189
185°
17.044
8.375
12.878
6 325
190°
19 001
9 335
10.921
5 365
195°
21139
10 385
8 783
4 315
200°
23.461
11526
6.461
3 17,4
205°
25.994
12 770
3.928
1930
2'0°
28.753
14 126
1.169
.574
212°
29.922
14 700
0.000
0.000
10.992 pounds to raise the water and force it into the pump. If
the water was 2120 it would give off steam equal in pressure to
that of the atmosphere, and we have no available force at all.
Absolute Pressure. 9
These relations between pressure and temperature are simply
those for aqueous vapor or steam. When air is present the pres-
sure will be higher for a given temperature. For this reason the
vacuum or pressure in a condenser is not that due to the temper-
ature of its contents as given in a table of the physical properties
of steam for it is not steam alone with which we are dealing but
a mixture of steam and air.
You are now in a position to appreciate what is meant by ' 'ab-
solute" pressure. It is the pressure reckoned from a complete
vacuum as are the pressures in the above table, and atmospheric
pressure which is the zero of the ordinary steam gage and of what
Fig. 6.
is referred to as "gage pressure" is about 14.7 pounds absolute,
varying with the barometer. In order to get the "absolute"
pressure then we must add the barometer's pressure, 14.7 pounds,
or 15 if we do not care to be very precise, to the pressure indi-
cated by the gage. The steam tables are given in absolute
pressures, and we have to take the absolute, not gage pressure,
when laying out the expansion line, or figuring problems in
which expansion is involved.
There is this difference between pumping air and water, that
io Pumping Air.
water is either there or not there; there is no half way about it.
It is neither expansible nor compressible by change of pressure,
and it may be handled in mass. In Fig. 6, for instance, we have
a closed vessel of water at A and another of air at B. Now when
the pump connected with A is operated a volume of, say one-
fifth, of the water is removed, the water left in the tank falls,
there is nothing to take its place, and a practically complete vac-
uum is left behind. But in the case of the air, when one-fifth of
the volume is removed by a stroke of the pump, the remainder,
instead of assuming a level and leaving a vacuum at the top as
the water did, expands and fills the whole space. Before the
pump was operated the air was at atmospheric pressure, say 15
pounds to the square inch absolute. The operation of the pump
removes one-fifth of its volume, and the remaining four-fifths ex-
pands to fill the complete volume. In this expansion, its pres-
sure would be reduced to four-fifths of the former pressure, equal
to 1 2 pounds, so that instead of having at once a complete vac-
uum in the chamber as with the water, we have only reduced the
pressure three pounds below the atmospheric pressure outside,
and if a column of mercury be connected with the chamber, as
shown at B, we shall find that in the case of the air it will only
stand about 6 inches in height, for the sustaining force is the dif-
ference between the inside and outside of the chamber, which is
15 — 12=3 pounds, and as one inch in height exerts a pressure
of one-half pound per square inch on its base, 3 pounds would
balance 3-^.5 = 6 inches in height. In this case there is said
to be 6 inches or 3 pounds of vacuum in the vessel.
By further reducing the air in the vessel, we can produce great-
er differences in pressure between the inside and outside and the
atmosphere will press the harder toward the inside of the vessel,
its pressure being measured in the inches of mercury which it
will lift, or the pressure per square inch which it exerts. All
questions in regard to a vacuum become plain when we consider
that the atmosphere itself exerts a pressure of nearly 15 pounds,
and measure everything from an absolute zero 15 pounds below
the atmospheric pressure.
When an engine is run without a condenser the steam with
which the cylinder is filled at the end of the stroke has to be
Production of Vacuum bv Condensation.
1 1
forced out against the pressure of the atmosphere, about 15
pounds to the square inch. It is possible from the nature of
steam to remove the atmospheric pressure with, in most cases, a
decided gain. One pound of steam at atmospheric pressure oc-
cupies 1 ,642 times as much room as it does in the state of water.
If therefore when the stroke has been completed and we are
ready for the piston to come back we inject a little cold water
into the spent steam, it will condense to about one 1600th of
Fie\ 7.
its volume, and leave a vacuum into which the piston can return
without having to force back the atmosphere. This is the way
the earlier engines were run, the condensation taking place in the
cylinder itself, and, moreover, the vacuum was all that made the
engine operative, for the steam carried was bul little above atmos-
pheric pressure. Watt's introduction of the separate condenser
was his greatest contribution to the steam engine, and constituted
12
Gain by Condeiisation .
his most important invention, for he was not as you know the in-
ventor of the engine, but its improver. The operation of the
condenser is shown in Fig. 7. The denser steam in the stuffing
box end of the cylinder is pushing the piston to the left, forcing
the spent steam of the previous stroke to the condenser where,
instead of having to be forced out against 1 5 pounds pressure of
the atmosphere, it is condensed by coming into contact with a
spray of cold water. The condensed water, the water of injec-
tion and the air which has entered with the steam and by leak-
age are drawn out by an "air pump," and the comparatively
small volume which it has to expel against the atmospheric pres-
sure, leaves a large margin a 95 lbs, b c
. , - ° I ABSOLUTE '
of power gained after that
required to run the pump
is deducted.
L,et us first consider the
nature and extent of the
saving due to a condenser,
and when it is and is not
advisable to use it.
Suppose we have an en-
gine with an initial pres-
sure of 80 pounds gage,=
95 pounds absolute, cutting
off at one-third. The
mean effective pressure, if the engine ran non-condensing and
made the perfect diagram represented by the full lines in Fig. 8,
would be 51.25 pounds. If we put on a condenser and reduce
the back pressure from that of the atmosphere, say 15 pounds ab-
solute, to 3 pounds absolute, the diagram, to give the same mean
effective pressure representing the same load on the engine, would
take the form shown by the dotted lines. •
In the non- condensing diagram, the boiler has to fill the cylin-
der up to the point C, and the volume of steam at cut-off is pro-
portional to the line A C. In the condensing engine the steam
is cut off at B, and the steam is proportional to the line A B.
Now A C is .33^3 of the volume of the cylinder and A B is only
.23256, so we have apparently saved
Fig, 8.
53 LBS. ABSOLUTE
Gain by Condensation. *3
-33333— 23256 ^ ioo==
•33333
about 30 per cent, (clearance neglected).
Again, suppose we have a throttle governed engine cutting off
at two-thirds the stroke, with an initial pressure of 50 pounds,
gage, =65 absolute, running non-condensing, it would make,
theoretically, the diagram indicated by the solid lines in Fig. 9,
and exert a mean effective pressure of 45.62 pounds. If we put
on a condenser and reduce the back pressure to 3 pounds, in which
case we should as before realize a vacuum of 12 pounds or 24
inches, the cut-off would remain at two-thirds, but the initial
pressure would be lowered, as shown by the dotted lines, to 38
pounds. While the volume up to cut-off is the same in each case,
95 lbs.absolute the pressure is lowered, and
the same volume of lower
pressure steam weighs less.
^ Suppose the size of the
cylinder was such that it
took a cubic foot to fill it up
to cut-off. Then, when
making the non-condens-
absolute zero Power. s. t. ing diagram shown by the
Fig. 9. solid lines in Fig. 9, it
would take a cubic foot of 50- pound steam (65 absolute) which
would weigh .1519 of a pound. When making the condensing
diagram shown by the dotted lines, it would take the same
volume of 53-pound (absolute) steam, which would weigh .1255
of a pound. An apparent saving of
•I5I9 -I255 >< 100 = 17.38 per cent.
.1519
This is not, however, a pure saving. The most important
charge against it is the reduction of available temperature for the
feed water. With an engine exhausting at atmospheric pressure
the exhaust steam has a temperature of 2120, and by the use of a
suitable heater it is possible to get the feed water nearly as hot.
With a condenser in which the absolute pressure is reduced to
three pounds, the temperature of the exhaust steam is only
141 62, and the temperature of the hot- well, or the discharge
from the air-pump, would be in practice from no° to 1200. Very
ATMOSPHERIC LINE
14 Loss in Feed Water Temperature.
careful practice might raise it to 1300 but the temperature of the
hot-well will always be considerably less than that due to the
pressure of the steam or vapor in the condenser, on account of
the impossibility of bringing every particle of steam into contact
with the water when only the exact quantity of water theoreti-
cally needed to condense it is used, and the raising of the pres-
sure in the condenser by the presence of air without a corres-
ponding increase of the temperature. Suppose the hot-well tem-
perature is no° as against the 2100 that we might have by run-
ning non-condensing. There would be a loss of approximately
10 per cent, for there is a gain in efficiency of one per cent for
about each ten degrees we heat the feed water. Even if we kept
the hot- well up to 1300 there would be a fall in the available tem-
perature of feed of 8o°, or approximately eight per cent.
Again, it takes a great deal of water to condense the steam,
and all this water, as well as the condensed steam and the air,
which has worked in with it and by leakage, must be pumped out
against the pressure of the atmosphere, so that the cost of sup-
plying the condenser with water and of operating the air pump
must be deducted from the apparent gain. There is also the in-
terest on the extra cost of the condenser, the extra repairs, sup-
plies, insurance and attendance if the condenser plant is large
enough to require especial attention.
Here is a little extract from Peabody's Steam Tables, giv-
ing the amount of the heat contained in a pound of steam at
absolute pressures of from 10 to 25 pounds, or from about 5
pounds below the atmosphere to about 10 pounds above. The
column marked "Heat of the Liquid" gives the number of
heat units that we would have to put into a pound of water
to bring it from 32 ° up to the boiling point (given in the
second column), at the corresponding pressure in the first col-
umn. It is unnecessary to tell those of you who have read the
previous lectures that a "heat unit" or "British Thermal Unit"
is the amount of heat necessary to raise a pound of water one de-
gree. In the column marked "Heat of Vaporization" is given
the "latent heat" or the number of heat units necessary to evap-
orate the pound of water into steam after it has been raised to the
boiling point. The "Total Heat" is the sum of the two. Now
suppose, the terminal pressure in the cylinder, that is, the. pres-
Water Required to Condense a Pound of Steam.
*5
sure at the time the exhaust valve opens, is 5 pounds above the
atmosphere, or say 20 pounds absolute, then every pound of steam
used will carry to the condenser 1151.5 heat units. Suppose the
hot- well temperature is 1200. A pound of water at 1200 con-
tains 88.1 heat units above 320 . Suppose again that the tem-
perature of the injection water was 6o° . A pound of water at
6o° contains 28.12 heat units above 320 . Then each pound of
water in raising from 60 to 1200 will absorb 88.1 — 28.12 = 59.88
heat units.
To condense the pound of steam and reduce it to water of
1200 we must take from it 1151.5 — 88.1= 1063.4 heat units.
A
4ft
"d
0"
Pressure,
Pounds per
Square Inc
mperature,
grees
Fahrenhei
3
w
03
A
+3
CO
-t-a
c
CM O
OS
3 J
03 Fh
«|
03 13
HA
O
O
>
10
193 25
1619
1140.9
979.0
11
197 78
166 5
1142 3
975 8
12
201 98
170 7
1143.6
972.9
13
205 89
174.6
1144.7
970 1
14
209.57
178.3
1145 8
967.5
15
213.03
181.8
1146.9
965 1
16
216 32
185 1
1147.9
962.8
17
219 44
188 3
1148 9
960.6
18
222 40
19! 3
1149 8
958.5
19
225.24
194 1
1150 7
956.6
20
227.95
196 9
1151.5
954.6
21
230 55
199 5
1152.3
952 8
22
233.06
202 0
1153.0
9510
23
235 47
204 5
1153 7
949.2
24
237.79
206 8
1154.4
947 6
25
240 04
209 1
1155.1
946 0
As one pound of water will absorb 59.88 units it will require to
condense each pound of steam
1063.4 ~^~ 59-88 = 17.7 pounds of injection water.
It will be noticed that the number of heat units absorbed by
one pound of water is very nearly the difference in temperature
between the injection water and the hot-well. This difference
in the case in question would have been 120 — 60 = 60 heat
units, and is near enough in any case for practical purposes. To
find the amount of water required for a condenser, subtract the
1 6 Cooling Water Required for a Given Engine.
heat units contained in a pound of water at the hot-well temper-
ature from the number of such units contained in a pound of
steam of the terminal pressure. These values can be gotten from
a table of the Physical Properties of Steam, to be found in any
engineer's reference book. Divide this value by the difference
between the temperature of the injection and of the hot- well, or
by the rise in temperature of the circulating water in the case of
the surface condenser, and you get the number of pounds of in-
jection or circulating water required per pound of steam. Mul-
tiply this by the number of pounds of steam required per hour
per horse-power, and you get the injection per hour per horse-
power. Multiply this again by the horse- power developed, and
you get the injection required to run a given engine with a given
load.
When the only water available for injection is foul, and would
make a mixture in the hot- well, that would not do to feed to the
boilers, ' a surface condenser may be used. This is the general
practice on sea-going steamers where the injection water is salt,
and it is necessary to use the same boiler water over and over.
Did you ever think what an immense amount of water is boiled
into steam to run one of the great liners ? The Paris has 30,000
horse-power. Suppose she runs on 13 pounds of steam per hour
per horse-power, her boilers would evaporate over a million gal-
lons of water a day, a good supply for a sizable town. Of course
they cannot afford to foul this by mixing the salt sea water with
it, so they condense it by letting it come in contact with metal
surfaces kept cool by sea water flowing upon the other side, but
always separated from the condensed steam. In this way it will
be seen the cooling or circulating water is kept entirely separate
from the condensed steam and the latter can be safely returned
to the boilers, while any sort of non-corrosive liquid can be used
for cooling purposes. We have heard of plants in large cities
where water was taken from the sewer, passed through a surface
condenser, and returned to the sewer again.
It will be noticed that the exhaust steam carries to the conden-
ser a very large percentage of the heat which it brings from the
boiler. A pound of steam at 80 pounds gage, 95 absolute, con-
tains 1 1 80. 7 heat units. Suppose 20 pounds of this steam are
required per hour per horse-power. Then 20 pounds of steam
Where a Condenser is not Advisable. 17
will do 33,000 X 60 — 1,980,000 foot pounds of work, one pound
will do 1,980,000-1-20= 99,000 foot pounds. As one heat unit
is equal to 778 foot pounds, the number of heat units transformed
to work would be 99,000 -f- 778=127. 4 heat units.
1180.7 — 127.4 = 1053.3.
We have 1 180.7 units of heat taken from the boiler, 127.4 of
them converted into work and the balance, barring the trifling
loss from radiation, going out in the exhaust. It follows that if
we have any use for heat at anything under the temperature of a
reasonable exhaust, it would be bad engineering to let this heat,
which might be applied to the purpose, escape into the river in
the overflow from a hot-well. One case then where it is inad-
visable to use a condenser is where it is possible to use the ex-
haust steam to advantage.
Again, suppose we had 80 pounds initial pressure and instead
of cutting off at one quarter we carried the 80 pounds for the full
stroke, and exhausted at atmospheric pressure our mean effective
pressure would be 80 pounds. Now, if we put on a condenser
giving us 12 pounds of vacuum, we must reduce the initial to 68
pounds gage. The volumes used would be the same in both
cases. Steam of 80 gage (95 absolute) pressure weighs .2165 of
a pound; at 68 pounds gage (83 absolute), .1908, a saving of
.2165 .1 90S vy 0
- - — X 100= 1 1. 8 per cent.
.2165
Now if we lose ten per cent by reducing the temperature of
our feed water, and it takes two per cent to run the air pump, we
shall be worse off with the condenser, than without it, to say
nothing of the investment in it, the cost of oiling, packing, at-
tending it, and keeping it in repair. Evidently here is another
case where we would be better off without the condenser.
In a' well-designed engine, the power required to operate the
pumps may be less than one per cent of that developed by the
main engine, and is sometimes as high as three per cent. This
percentage or more of the steam supplied may be used according
as the pump is operated from the engine itself, or by an inde-
pendent cylinder more extravagant in the use of steam.
In order to understand one of the points that bears on the de-
sirability of the condenser in a special case, it is necessary to un-
1 8 Effect of Cylinder Condensation.
derstand something of the cylinder condensation. When steam
contains just the number of heat units per pound given in the
tables, that is, just enough to evaporate it into steam, it is said to
be "saturated." This means that it is saturated with heat, not
with moisture. The term is apt to be misunderstood, and I have
frequently talked with engineers who could not get rid of the
idea that "saturated" steam must be soaking wet. The ordin-
ary steam that we get from boilers carries with it more or less
moisture, and steam is "commercially dry" when it has no more
than two per cent by weight of such moisture. If we apply heat
to such steam, and dry it out or evaporate the moisture, we shall
have "saturated" steam at the instant that all the moisture is
gone, and if we continue the heating so as to increase the tem-
perature above that due to the pressure, we shall have ' 'super-
heated" steam.
Now, unless steam is superheated, it cannot lose a particle of
heat, except by expansion, without a corresponding amount of
condensation. Steam' of 80 pounds gage (95 absolute) pressure
has a temperature of about 3240 F. As it is expanded in the
cylinder after cut-off its temperature falls, and during the ex-
haust stroke the temperature is that due to the back pressure;
2120 if the exhaust is against the atmosphere, 141. 6° with a con-
denser reducing the absolute back pressure to 3 pounds. As a
consequence, the cylinder and piston heads, the ports, and wall
of the cylinder, having been in contact with this cooler steam,
have had their temperature reduced and when the live steam en-
ters at the beginning of the stroke, it finds itself in contact with
surfaces comparatively chilly, and therefore has to part with
enough heat to raise these surfaces to its own temperature before
it can continue to exist as steam in contact with them. As a re-
sult, there is a large amount of condensation at the beginning of
the stroke, and this continues up to the point of cut-off. As the
steam commences to expand its temperature is reduced, the sur-
faces begin to give back the heat that has been expended upon
them, and the water resulting from the initial condensation com-
mences to boil under the diminished pressure, as did the water
when we cooled the flask in lecture I. Meantime, however, the
piston is uncovering new cylinder wall, which requires to be
heated, and this action will continue to a point where the temper-
Effect q/ Cylinder Condensation. 19
ature which the wall has assumed equals the temperature of the
expanding steam. Beyond this point all the surfaces are hotter
than the steam and the re- evaporation is more rapid. Except on
very slow running engines, however, this re-evaporation during
the working stroke is not very extensive. In a good tight en-
gine at ordinary speeds the expansion line usually agrees very
well with the theoretical curve, commonly rising a little above it
at the later portion, showing that the re-evaporation but little
more than makes up for the condensation due to the conversion
of some of the heat units into work, and to radiation. In this
way the re-evaporation during the working stroke is a benefit,
but the greater part of the evaporation occurs during the exhaust
stroke, when the resulting steam can do no good, but is escap-
ing to the atmosphere, or the condenser. When the pressure is
reduced by the opening of the exhaust valve, the moisture in the
cylinder, being above the boiling point at the reduced pressure,
passes rapidly into steam, the heat for its continued evaporation
being furnished by the containing surfaces, and these containing
surfaces chilled by this abstraction of heat, must be heated
again on the following stroke. The wall never gets as cool as
the exhaust temperature, and probably never as hot as the in-
itial steam. The longer the time it is exposed to a temperature
lower than the initial and the lower the temperature of the ex-
haust, the greater will be its range of variation. Notice that
the surfaces must give up to the outgoing steam exactly as
much heat as they receive from the incoming steam. They cer-
tainly cannot give up any more, and if they did not give up as
much as they got, heat would accumulate and melt them down.
This subject of cylinder condensation is one of the most inter-
esting and important connected with steam engineering. Exper-
iments indicate that the loss from this action is rarely less than
20 per cent in simple unjacketed cylinders of ordinary automatic
engines, and it may be much more. The point I want to call
your attention to in connection with our present subject is that
the greater the difference between the initials and back pressures,
the hotter the steam the cooler the exhaust, the greater this ac-
tion and loss will be. Further, the earlier in the stroke the cut-
off occurs the greater the initial condensation, because of the
greater variation of temperature on the working stroke and the
2o Diagram of Maximum Efficiency.
greater proportion of the time that the temperature of the steam
in the cylinder is below that of the steam chest. The condensa-
tion will also increase wTith any increase in the proportion which
the area of the containing surface bears to the volume of steam
contained.
In an indicator diagram like Fig. 10, the space E B represents
the volume of the cylinder including clearance up to the point of
cut-off, while the shaded area is proportional to the work done.
The volume that must be filled with steam at each stroke will
bear the smallest proportion to the work done when as in Fig. 3
the cut-off is at such a point that expansion extends just to the
line of back pressure, making the diagram end in a point; and
compression extends just to initial pressure. The higher the in-
itial pressure and the lower the back pressure, the greater will be
the number of expansions used, and the greater the area of the
diagram compared with the ^ a b
volume up to cut-off. But
every engineer knows that,
notwithstanding the fact
that the steam accounted
for by the diagram per
horse-power would be the
least in amount under these . *N**r.
conditions, it would be very ^>' IO'
poor economy to run an engine with so light a load. We might
continue the reduction of the diagram on these lines until the power
developed is barely sufficient to run the engine itself, in which case,
even if we got a very low rate of steam consumption per indicated
horse-power, the little useful power we would get would be very
expensive. As a matter of fact, however, we should use more
steam per indicated horse-power, for the gain by expansion falls
off rapidly as the number of expansions is increased, while the
loss by cylinder condensation increases at a rapid rate. Conse-
quently, there is a point where the loss from cylinder condensation
equals the gain from increased expansion, and any increase of ex-
pansion will result in a loss. The more power we can get out
of the cylinder the less proportion will the radiation and frictional
losses bear to the power delivered to the shafting, so that it is not
found economical in practice to cut off much earlier than one-
• Independent and Direct Driven Condensers. 21
quarter stroke, in an ordinary single-cylinder non-condensing en-
gine without jackets; nor to expand much below the atmosphere
with a simple condensing engine. Obviously then, if an engine
is cutting off at one- fifth stroke, or earlier, there will be little
chance of increasing the economy by putting on a condenser. It
is possible to extend the point of cut-off without increasing the
mean effective pressure by lowering the boiler pressure, or throt-
tling it at the engine, but here the efficiency of the high pressure
steam is sacrificed, and it is still an open question how far it is
safe to go in this direction. I commend it to you as a subject for
profitable discussion, whether with an underloaded engine, con-
densing or not, it is profitable to reduce the initial pressure and
if so under what circumstances and to what extent.
Condensers may be divided into two general classes. Those
whose air pumps are driven by the main engine.
Those having their own independent motive power.
The first type includes belt and gear driven pumps as well as
those directly attached to the working parts of the engine itself.
The advantage claimed for them is that the power required to
drive them is generated in the large economical cylinder to much
better advantage that it can be in a small cylinder of a direct act-
ing pump, such as is usually used to operate the independent con-
denser.
On the other hand, the advocates of the independent conden-
ser claim that while the attached air pump is constrained to move
at the same speed as the main engine or a speed proportional
thereto, regardless of the amount of work it has to do, the inde-
pendent air pump can be run fast or slow according to the amount
of water passing, which varies with the load and the vacuum car-
ried. They further claim that the steam from the cylinders
which operate the pump can be used to heat the feed-water, thus
doing away with 1 he loss noted above, and that as practically all
the steam required to run the pump is thus utilized, it does not
matter if the pump is not so economical as the main engine.
Many of both types of condenser are used and each has its ad-
vocates. If one is very decidedly better than the other, it will
in time appear, and the fittest will survive or perhaps as in many
other cases it will be found that each is particularly adapted to
special circumstances.
^2
The Vertical Air Pnmt>.
The amount of work done by an air pump depends not upon
the size of the piston, or the speed at which it runs, but upon the
amount of water and air that it forces out of the condenser
against the pressure of the atmosphere. In Fig. n, when the
bucket or piston rises, it leaves a vacuum behind it. Suppose
that the water line A B just reached the diaphragm CD when
the bucket was in its highest position, without lifting the valves.
Then when the bucket descended it would leave a vacuum above
it, and if no water is let in to raise the level A B the bucket will
continue to move up and down with a vacuum above and below
it, without doing any work or calling for any power except to
overcome its own friction. Now if we let a little water into the
chamber B, a corresponding
amount will pass through the
bucket on its downward stroke,
increasing the amount above
the bucket and the water line
A B will come in contact with
the diaphragm C D before the
upward stroke is completed,
lifting the valves in that dia-
phragm, andmaking the pump
complete the stroke against
the atmospheric pressure. /7^
This is where the work of the
pump comes in, and this will
be dependent upon the quanti-
ty of water passed, for if we p^ II#
put in twice the amount of
water, the valves in C D will be open twice as long and the bucket
travel twice as far against the atmospheric pressure. Of course
there would be a saving, so far as friction is concerned, if the
pump could be run slowly enough to completely fill at each stroke,
instead of making several strokes to do an equivalent amount of
work, but it is not constantly working against a vacuum as many
suppose.
It is quite generally conceded that the vertical form of air
pump, although necessarily single acting, is preferable to the
double acting horizontal pump. This is due to the certainty of
Sealed Glands — Surface Condensers 23
its action in taking water through the bucket valves, to the
quick and positive closure of the valves, to the facility with
which the water will collect in the bottom of the pump during
the up stroke ready for the bucket when it descends. The flow
is always in one direction, the water always lies on the valves
so as to keep them air tight, and very little clearance is necessary
between the foot and bucket valves and between the bucket and
head valves. The glands around the vertical rods can be cupped
and filled with water, to seal them against air leaks. It don't
hurt a vacuum any to have water leak into it, but a little air will
make a big difference, so that if you can keep water around a
place where air is likely to get in you will have a better vacuum.
I have heard of serious breaks in condensing apparatus being got-
ten over at sea by building a coffer dam around the fracture and
keeping it full of water. This kept it sealed against the atmos-
phere, and some water simply went through the crack instead of
through the injection valve.
Of course the air pump must be large enough to keep the con-
denser clear at times of maximum load or when the greatest
amount of water and air is to be handled. On the other hand, it
should not be too large so as to cause unnecessary loss by fric-
tion. The indications are that past practice has been too liberal
in this respect and that many engines have labored along with
cumbersome pumps where smaller sizes would have been ample.
It would appear, too, that good design lies in the direction of
short strokes and large diameters, for if we quarter the stroke of
a pump and double its diameter, it will have the same capacity,
the force required to overcome the friction will be exerted through
only one- quarter the space, and will be no more than twice what
it was before for the rubbing surface, the circumference of the
bucket has only been doubled, and in a vertical pump where the
bucket is always covered with water, this may be an easy fit.
The larger bucket also gives greater capacity for the valves and
the speed of the water through the larger passages thus afforded
is slower.
If you are interested in proportioning surface condensers, I ad-
vise you to read a paper on the subject by J. M. Whitham, page
417, Vol. IX., Trans. Amer. Soc. Mech. Engrs. In it he consid-
ers all the factors bearing on variable conditions and gives formu-
24
The Injector Condenser.
lae which meet all conditions. For the average case, he gives a
very simple formula for the amount of cooling surface required.
Multiply the total number of pounds of steam conde?ised per
hour by ij and divide by 180.
This allows nearly one-tenth of a square foot of cooling surface
per pound of steam, which would not be a bad figure to bear in
mind.
A condenser may fail to work from a failure of the injection or
circulating water supply, in which case the steam will not be con-
densed, but will accumulate in the condenser, destroying the vac-
uum and heating the condenser
up. Relief valves which open
automatically to the atmos-
phere when the pressure in
the condenser exceeds that
outside are usually provided
to allow the engine to keep on
running non- condensing until
the trouble can be located and
remedied. Secondly, a con-
denser may fail to work on ac-
count of the failure of the air
pump to remove the water and
air as fast as it comes to the
condenser. Such a failure is
apt to result seriously, for if
there should be a vacuum in
the cylinder at such a time,
as there is likely to be by expansion in the low pressure cylinder
of a compound or triple expansion engine, or even in a single
cylinder engine when starting or stopping, or when lightly loaded,
the water will draw into it and result in a break down. For this
reason condensers are often, and should always be provided with
a device for automatically admitting air and breaking the vacuum
when the height of water in the condensing chamber exceeds a
safe limit, and care must be taken that nothing occurs to slow
down the air pump if indirectly connected or independent.
You remember the experiment we performed with the long
tube of mercury. The action would be just the same with water
Fisr. 12.
The Injector Condenser.
25
RELIEF VALVE
enly it would take a longer column of water to balance the pres-
sure of the atmosphere. In Fig. 12, if the tank were originally
full of water, the water would run out through the pipe until the
column is just sufficient to balance the pressure of the atmos-
phere, which will be 34 feet more or less according to the tem-
perature of the water and the height of the barometer. If, then,
we have the pipe over 34 feet long, water will run out of the
chamber by its own weight against the atmospheric pressure,
leaving a vacuum in the chamber. If we let steam and cool
water together into such a chamber, the steam would be con-
densed, the water would flow out without
the necessity of a pump, and the vacuum
would be maintained without the bother
and expense of pumping the water out.
There is one fatal objection to the opera-
tion of this ideal scheme. We have seen
that the steam and the injection water
bring into the condenser more or less air
to say nothing of that which steals in
through leakage. *As the air would not
fall out by gravity, it would gradually ca-
cumulate and destroy the vacuum. This
objection is very ingeniously and simply
gotten over in the injector or ejector con-
denser, shown in Fig. 13. The exhaust
steam enters through the nozzle A. The
injection water surrounds this nozzle and
issues downward through the annular
space between the nozzle and the main
casting. The steam meeting the water is
condensed, and by virtue of its weight and of the momentum which
it has acquired in flowing into the vacuum the resulting water
continues downward, its velocity being further increased, and the
column solidified by the contraction of the nozzle shown. The air
is in this way carried along with the water and it is impossible
for it to get back against the rapidly flowing steam in the con-
tracted neck. The condenser will lift its own water twenty feet
or so. When water can be had under sufficient head to thus feed
itself into the system, and the hot- well can at the same time be
26 Cooling Towers. Co?idensi?ig by Evaporatioii.
so situated as to drain itself, it makes a remarkably simple and
efficient arrangement. In case the elevation is so great that a
pump has to be used to force the injection, the pump has to do
less work than the ordinary air pump, and its exhaust can be
used to heat the feed water.
Except under exceptional circumstances, the nature of which
we have tried to indicate, the gain by the use of a condenser is so
great that their use is very general in plants where water can be
had for condensing purposes, and it is an important point for con-
sideration in locating a plant, whether or not a supply of suitable
condensing water will be available. In large cities where water
must be bought at a considerable cost, plants are run non- con-
densing at a great sacrifice of steam efficiency, because it would
be out of the question to buy water for injection. Considerable
has been done in the way of cooling water off after it has passed
through the condenser, and using it over and over again. This
is done by letting it trickle over a series of pans on the roof, or
letting it fall in a shower through a shaft through which a cur-
rent of air is circulated.
In this connection, there has recently appeared on the market,
an apparatus, which appears to promise well. You know as much
heat must be taken out of a pound of steam to reduce it to water
of a given temperature, as would have to be put into the water to
make it into steam from that temperature. Suppose the steam
from an engine cylinder is discharged through a series of pipes
upon the outside of which cold water is sprayed. Part of the
water, as it strikes the heated surface, will be evaporated and es-
cape into the atmosphere as vapor, but for every pound of water
so evaporated a pound of steam is condensed, and can be used as
boiler feed. Thus, instead of using the city water for boiler feed,
we use it to spray the condenser, and use the condensed steam
over and over in the boilers, and if, as it appears, and as the mak-
ers of the apparatus assure us, it takes no more water in one
case than in the other, we are ahead whatever net benefit we can
get out of the vacuum.
It is a mistake to strain for too high a vacuum. Of course
every particle that you can save by keeping things free from air
leakage is so much pure gain. What I mean is don't crowd your
circulating pump or open your injection too wide just to get the
Situation of Pump. Lifting Valves. 27
last fraction of an inch of vacuum. The amount of water to be
handled to get an additional half inch at the lower end of the
gage is excessive, the temperature of your feed is reduced, and
while it may mean less pounds of steam per hour per horse- power
for the main engine, it is likely to mean more dollars per year
per useful horse-power delivered. If you do not use the hot-well
water for boiler feed, or if you have methods by which this may-
be heated, that would allow you to run a lower hot- well tempera-
ture to advantage. Suppose, for instance, you have an econo-
mizer of ample capacity, heating the water with the waste of the
uptake, then it would pay you to run a higher degree of vacuum,
for if your economizer is ample, it will deliver the water to the
boiler at about the same temperature whether it comes to it at
100 or 130, and, so long as you do not make your pumps do as
much extra work as the extra vacuum amounts to, you are
ahead. When cold water is used for feed or when there is a
very considerable difference between the hot- well and exhaust
steam temperatures, and the hot- well water is used for feed, the
water may be passed through a heater placed between the engine
and the condenser. The exhaust will have a temperature of
about 1200 and will impart considerable heat to the feed, leaving
so much less for the condenser to do.
You will understand, of course, from what has been said of the
nature of a vacuum and of the nature of pumping that no pump,
however powerful, can lift water out of the condenser by suc-
tion because the atmosphere cannot act upon the water to force
it up to the pump. The pump must, therefore, be situated be-
low the condenser, so that the water can fall into it by its own
weight or head. Further, there must be no chance for any ac-
cumulation of air or the pump will get air bound and simply
work back and forth without taking any water.
A common annoyance connected with the running of an air
pump is the hammering or clattering of the discharge valves, due
to the variations in pressure as the air and water are discharging.
This can be avoided by connecting a small pipe with a valve into
the passage leading from the water cylinder to the delivery valve,
and admitting a small quantity of air, the amount to be admitted
being only sufficient to overcome the hammering. This air can-
not vitiate the vacuum in the condenser, as it aids the water in
keeping the inlet or foot- valve closed. The pipe should extend
to an elevation greater than the hot-well for otherwise the water
and the air will discharge from it on the down stroke of the
bucket.*
^Constructive Steam Engineering, J. M. Whitham, p. 464.
THE JET CONDENSER.
In Fig. i we have a vessel filled with steam at atmospheric
pressure. Attached to it is a U-tube filled with mercury, open to
the atmosphere at the outer
end. As long as the inside
and outside pressures are
equal, the mercury will be at
the same level in both legs of
the tube, as shown. If we
inject a spray of cold water in-
to the vessel through pipe W,
the steam will be condensed
and will fall to the bottom,
occupying only the small
space below the dotted line
AB in Fig. 2. The space
above the dotted line will now
be empty, or, in other
words, a vacuum, and since
the pressure on the inside is
removed, the mercury will
rise in one leg of the tube
as shown. If we continue
to supply steam and con-
densing water to the vessel
and draw out the condensed
steam and water as fast as
it accumulates, we can main-
tain a constant vacuum in the vessel. This was the principle
upon which the early mining pumps were operated. The piston
Arrangement of Jet Condenser.
29
was drawn to the top of its stroke by the descending pump
plunger; steam at atmospheric pressure was admitted under the
piston and condensed by a spray or jet of water, thus creating a
vacuum. The pressure of the atmosphere then forced the piston
down, raising the pump plunger at the other end of the beam.
STEAM FROM BOILER OR
HIGH PRESSURE CYLINDER
The same thing is done on a larger scale and in a more scien-
tific manner by the jet condensing apparatus of today.
An entire apparatus of this type including all pipes and valves,
and connected to an engine cylinder, is shown in cross-section by
30 Types of Jet Condensers.
Fig. 3. The engine piston is moving to the left, and the exhaust
steam is passing out through the lower left-hand port into the
exhaust pipe and from there into the bottle-shaped condenser.
As it enters the condenser it meets a spray of cold water issuing
from the injection pipe around the edges of the cone S; this spray
condenses the steam and the intermingled steam and water pass
down into the lower part of the condenser and the suction cham-
ber of the air pump. This leaves a vacuum in the condenser and
exhaust pipe and the engine cylinder up to the piston face.
When the air pump bucket starts on its upward stroke, the
mingled air and water pass by gravity up through the foot valves
of the air pump. When the air pump bucket descends, the water
and air pass up through the bucket valves to the upper side of
the bucket or plunger. The next upward stroke of the bucket
forces the water out through the head valves of the pump into
the discharge pipe, at the same time allowing more water and air
from the condenser to pass up through the foot valves into the
lower part of the air cylinder. This action is continuous and the
air-pump speed must be regulated to handle the condensed steam,
the water required to condense it and the air brought in by the
water.
L,et us consider some of the general features of the jet conden-
ser, and particularly the apparatus shown.
First among these is the fact that the injection or condensing
water and the condensed steam are mixed together. If the con-
densing water is pure the air pump discharge is suitable for boiler
feed, but if the condensing water is impure, acidulous or salt, it
is evident that the water discharged from the air pump is unsuit-
able for boiler use. Second, there is to be considered the type of
air pump and the means by which it is driven. This pump may
be of the horizontal or vertical type, single cylinder double acting,
dDuble or twin cylinder single acting or duplex; it may be inde-
pendently steam driven, as in Fig. 3, or it may be driven by a
belt from the main engine or shafting or by an electric motor.
The independent steam driven type has the advantage of being
absolutely independent of the main engine; it may be started be-
fore and stopped after the main engine, thus establishing a vac-
uum before the load is thrown on the engine and draining the
cylinder and pipes of the water of condensation and leakage. It
Automatic Vacuum Bicakers and Relief Valves. 31
may be run at any speed within its limits, keeping the vacuum
constant under changes of load; it may also be placed at any con-
venient point near the engine. On the other hand, it is more ex-
pensive to operate than the belt or electrically driven type, as the
latter obtain their power at the same cost per horse-power as that
of the large units. We will not discuss here the relative econ-
omy of the different types. Another point of importance is the
possibility of damage or inconvenience through the failure of the
condensing apparatus or the improper arrangement of the con-
necting pipes. In case the air pump fails to operate or the in-
jection pipe becomes clogged, the engine must be shut down un-
less it is provided with another passage for the exhaust. The
usual method is to provide an atmospheric exhaust outlet, which
will allow the engine to exhaust into the atmosphere. As shown
in Fig. 3, this outlet is provided with an automatic relief valve A.
This is so arranged that when there is a vacuum in the exhaust
pipe between the engine and condenser the atmospheric pressure
on the outer side of the valve keeps it closed. If the air pump
becomes inoperative, the pressure accumulates in the exhaust
pipe and condenser and forces the valve open, allowing the engine
to exhaust freely into the atmosphere. When the vacuum is re-
established and the inside pressure falls below that of the atmos-
phere, the valve closes automatically. This valve may be a
special swing check or any one of a number of other special
valves made for the purpose. The gate valve B is intended for
use in case of repairs to the condenser; it may be closed tightly
and the automatic valve A locked open, when the condenser or
air pump may be repaired without interference from the hot ex-
haust steam. In case the condenser and air pump are connected
to injection and discharge mains common to other condensers the
gate valves C and D are necessary in the event of repairs to the
condenser or pump; the valve C is, however, primarily intended
to regulate the supply of injection water as will be mentioned
later.
Another source of trouble in jet condensing engines is the pos-
sibility of getting water into the engine cylinder and so wrecking
it. Suppose the air pump to be running but slowly, or to stop
entirely, so that it will not draw out the injection water as fast as
it runs into the condenser. Eventually the water will flood the
32
Types of Vacuum Breakers.
condenser and pipes, enter the cylinder and wreck it. To render
this impossible, two methods are adopted: one is the application
of a vacuum-breaking device to the condenser; the other is to so
arrange the spray cone and condenser neck that an accumulation
of water will reduce the surface of the spray and break the vac-
uum.
Fig. 4 shows a patented vacuum-breaker furnished on all Geo.
F. Blake & Knowles' condensers. Its action will be understood
from the cut. When the
water rises in the condenser
to the level AB, it lifts the
float F, which in turn lifts
the air valve V from its
seat, admitting air to the
exhaust pipe and engine
cylinder through the pipe
P, thus breaking the vac-
uum. This, of course,
equalizes the inside and
outside pressures, and pre-
vents any more water from
flowing into the condenser.
The engine exhaust will
then accumulate until it
acquires sufficient pressure
to lift the valve A, Fig. 3,
and the engine will ex-
haust into the atmosphere.
Fig. 5 shows the arrange-
ment of condenser neck and
spray cone used upon the
Worthington condensers to
accomplish the same result.
In this case the water is sprayed downward, and as the con-
denser neck is quite small, the rapid condensation is due only
to the large surface exposed by the spraying water. Owing
10 the small size of the condenser, any accumulation of water rap-
idly diminishes the condensing surface until the spray itself is
submerged, leaving only the small annular ring of water at A B
How to Start and Stop a Condensing Engine.
33
.
2^-
EXHAUST
STEAM
7 /I
^_\%-~S(
-B
3 RAY CONE
to act on the large volume of steam from the engine. The sur-
face of this ring is far too small to condense the steam and the
pressure immediately accumulates and either the valve A, Fig.
3 opens, allowing the engine to run non-condensing or the ex-
haust steam blows out through the injection pipe and pump
valves.
Again, the engine itself may draw water up into the low pres-
sure cylinder. Suppose a compound engine having a low pres-
sure cylinder of 4 times the area of the high pressure. In start-
ing up or shutting down the engine
the throttle is barely cracked, as
usual, admitting throttled steam of,
say, 20 pounds absolute pressure
for the full stroke. At the end of
the stroke this seam will be admit-
ted to the low pressure cylinder,
where it expands to 4 times its
volume, or to about 5 pounds ab-
solute pressure. This is equivalent
to a vacuum of about 20 inches.
Now suppose the air pump to be
almost or entirely stopped and the
injection valve to be open as usual.
Then when the low pressure piston
starts on its return stroke, the ex-
haust valve opens, connecting the
cylinder under 20 inches of vacuum
with the exhaust pipe and conden-
ser, also under a vacuum; the at-
/w.jv.r. mospheric pressure will continue
to force water up into the condenser, and, if the air pump
cannot remove it, up into the engine cylinder. This would be
prevented by the vacuum-breaking device shown in Fig. 4.
This brings us to the proper method of starting and stopping an
engine with an independent condensing apparatus. To start the
apparatus, proceed as follows: Open slightly the injection valve
C and start up the air pump to its normal speed. This produces
a vacuum in the pipes and condenser, drains them of all water,
and causes the injection water to flow into the condenser. When
Fig. 5
HYi
34 Starting a Balking hijection.
the vacuum is established, as shown by the gage, open the throt-
tle and turn the engine over slowly, warming it up. Then bring
the engine up to speed, throw on the load and regulate the
amount of injection water by the valve C. The wheel on the
top of the condenser is used only for regulating the thickness of
the spray and has nothing to do with the supply of injection
water.
The speed of the air pump and the amount of injection water
must be regulated according to the load on the engine and the
amount of vacuum desired.
When several condensers are connected to a common injection
main, it sometimes happens that starting up the air pump of an idle
condenser will fail to bring water in through the injection branch.
This is partly owing to the fact that the greater vacuum already
established in the other condenser draws the water away from the
condenser in question, but in a greater measure it is due to the fact
that a flow of water at a high velocity is aheady established to the
other condensers. This stream of water requires some force to
break its flow and to divert a portion of it into a branch pipe, just
as the stream of water from a hose nozzle will remain a smooth
rod of water for some distance from the end of the nozzle, or just
as the jet of water into an injector tube passes the spills or over-
flow holes without losing a drop of water through them.
In such event, recourse must be had to the forced injection or
priming pipe shown in Fig. 3. This forced injection takes its
supply from a source under a very slight head or pressure, such
as a surge tank slightly elevated or the city water supply. If the
water will not come to the condenser, allow the air pump to run, close
main injection valve C, open fully priming valve E, and admit
water until a vacuum is formed in the condenser; then open gradu-
ally injection valve Cand close priming valve E gradually, when
it will be found that the flow of water to the condenser is estab-
lished. When this forced injection does not overcome
the trouble entirely, it will usually be found that the injection
pipes are too small, making the velocity of flow too great. In
such cases, the velocity of flow should be decreased by increasing
the size of the injection main and branches.
When shutting down an engine with an independent condens-
Stopping an ungine with an Independent Condenser. 35
ing apparatus, close the engine throttle first, and when the engine
has stopped, and not until then, close the injection valve C, and
lastly shut down the air pump. By shutting off the water supply
before the air pump is stopped, the water already in the con-
denser and pipes is pumped entirely out and there is no danger of
it getting into the engine cylinder.
THE SURFACE CONDENSER.
Suppose that we have a cylindrical vessel arranged as in Fig.
6, with a pipe through the center, leaving an annular space out-
side of the pipe. If we fill the annular space with steam and run
a stream of cold water through the pipe, the steam will condense
upon the cold pipe surface and fall to the bottom of the vessel,
leaving a vacuum above it. If we draw off this condensed steam
and the air it brought in
with it, we can refill the
vessel with steam and, by
running more cold water
through the pipe, condense
this new steam; this opera-
tion can be continued in-
definitely and a constant
vacuum maintained in the
vessel. In this case, we see
that the exhauster draws
out only the condensed
steam and entrained air,
the cooling water being
kept entirely separate.
In the jet condensing arrangement shown in Figs, i and 2, it
is plain that the condensing water flows into the vessel on account
of the vacuum therein; while in this case the part of the vessel
which is under a vacuum is, as we said above, entirely separate
from the condensing water, making it necessary to force the water
through the pipe by some other means
This is exactly the manner in which the surface condenser
operates.
Fig. 7 shows a sectional view of a complete surface condenser
and pumps.
o
Power. N.T.
37
38 Description of Surface Condenser.
The exhaust steam from the engine enters the condenser
through the elbow on top; it then expands and fills the space out-
side of and between the condenser tubes. The circulating pump
shown at the left draws its water by "suction" from any con-
venient source and circulates it through the tubes, keeping them
cold. The exhaust steam is condensed by contact with these cold
surfaces and falls to the bottom of the condenser. It is then
drawn off by the air pump shown at the right, and is usually dis-
charged into a hot well. The drawing shows clearly that the
condensed steam, being outside the tubes, is kept entirely separate
from the condensing water, which is forced through, the tubes.
Evidently then, the condensed steam discharged by the air pump
may be used over again in the boilers, even if the cooling water is
unfit for use, the only objection to this being the oil brought down
by it from the engine cylinder and steam chest. There are several
more or less satisfactory methods of extracting this oil or grease
from the water; a discussion of their merits is beyond the province
of this article. The condensing water is handled by a separate
pump and does not flow into the condenser, as in the case of a jet-
condensing apparatus; it may be salt or impure, and unless warm
water is required for some outside purpose it is discharged to
waste.
It is thus seen that a surface condensing apparatus requires two
pumps of comparatively small size as against one large pump for
the jet condenser. It is considerably more expensive than the
latter, and is seldom used except where it is desirable to return
the condensed steam to the boilers.
The possibilities of trouble from it are less than in the jet con-
denser. There is no way in which the condensing water can get
into the engine cylinder; while the condensed steam might, under
certain conditions of air pump operation, accumulate until it
reached the top of the condenser, it could not get into the
cylinder, for the condensing surface would be entirely submerged
and the accumulated pressure would force open the automatic at-
mospheric relief valve and allow the engine to exhaust into the
atmosphere.
There is the same need of an atmospheric exhaust outlet as in
the case of the jet condenser and for precisely the same reason.
The piping between the engine, the elbow on the condenser, and
Types of Air Pumps.
39
the atmospheric exhaust should be the same as in Fig. 3. In (he
type of apparatus shown, the condenser is directly attached to the
pump or pumps. This is not at all necessary; the air or circulat-
ing pump or both may be placed at any convenient point and con-
nected with the condenser by pipes. The air pump, however,
should be placed below the condenser, so that the condensed steam
may go to it by gravity. Nor is it necessary to use the type of
pump shown by the drawings. The pumps may be horizontal or
vertical; of the single or double-acting single- cylinder type; the
single-acting twin-cylinder type; or the duplex type. Fig. 8
shows a horizontal double-acting cylinder air pump, independently
£=0
Fig. 8.
steam-driven, which is frequently used with both jet and surface
condensers. The condenser outlet is connected with the suction
inlet of the pump, and its operation is the same as any double-act-
ing pump.
Centrifugal pumps are frequently used as circulating pumps,
and various combinations of pumps and condensers are made.
Fig. 9 shows a surface condenser equipped with 3-cylinder ver-
tical reciprocating air pumps and centrifugal circulating pumps,
both pumps being driven by electric motors. The details of the
condenser itself vary: for instance, a jet condenser is frequently
box-shaped instead of bottle or cone-shaped as in Fig. 3; a sur-
face condenser may be rectangular in cross section instead of
cylindrical, as in Fig. 7; the steam may be inside and the water
outside the tubes of a surface condenser, instead of as shown in
Fig. 7; etc., etc. The principle is the same, however, in all ar-
4o
Motor- Driven Air and Circulating Pumps.
rangements; in a jet -condensing apparatus the steam is condensed
by contact with a jet or spray of cold water and the air pump
handles the condensed steam, the condensing water and the air
entrained in both; in a surface condensing apparatus the steam is
condensed by contact with a cold surface and the air pump handles
EXHAUST INLET
the condensed steam and the air, while the circulating pump
handles the condensing or circulating water alone.
THE INJECTOR OR SIPHON CONDENSER.
Fig. 10 is a small ^cale reproduction of the jet condensing ap-
paratus described in Fig. 3. It will be seen that with the arrang-
ments shown, an air pump is required to pump out the condensed
steam, the condensing water and the air brought in by both.
If the hot well were lowered to a point about 34 feet below the
condenser, as shown by the
dotted lines, it will be seen
that an air pump is not re-
quired to remove the con-
densed steam and the water.
This will be plain if it is
remembered that a perfect
vacuum of 30 inches in the
engine exhaust pipe will
not support a column of
water in the discharge pipe
more than 34 feet high; so
that if any water is sup-
plied to the condenser in
excess of this 34- foot col-
umn it will pass through
the condenser and out of the
discharge pipe without the aid of a pump. Now, if the neck of
the condenser be contracted, as in Fig. 11, the velocity of this
falling water will be greatly increased, and the water will carry
out with it not only the condensed steam but the air, leaving a
vacuum in the exhaust pipe.
This is the principle of the injector or siphon condenser, one
type of which, the Bulkley, is shown in cross-section in Fig. 12.
As will be seen from the figure, it is not necessary to place the
42
Principle of Injector Condenser.
O
O
o
o
£
condenser below the engine, as in Figs. 10 and n. All that is
required is to have the column of water between the condenser and
the hot well as great or greater than the vacuum will support, so
that the constant supply of condensing water will produce a con-
tinuous downward flow. In the arrangement shown the hot well
is a little below and the condenser is above, the engine level, an
ordinary tank pump being used to elevate the condensing water.
The exhaust steam enters the top of the condenser and passes
through the inner cone or nozzle C. The condensing water enters
the condenser at the side and
passes downward around the ex-
haust nozzle in a thin conical
film. The exhaust steam is con-
densed within this hollow cone of
falling water, and the condensed
steam and the condensing water
then fall vertically through the
condenser, and discharge pipe.
In passing through the neck of
the condenser the water acquires
sufficient velocity to draw out
with it the entrained air, leaving
a vacuum in the exhaust pipe
and engine cylinder. The lower
end of the discharge pipe is
sealed by the water in the hot
well. It is necessary to provide
a large condensing surface, as
well as a high velocity for the in-
jection water; in most condensers
of this type this is provided for by
bringing the exhaust steam in
through the cone or nozzle C, and
the injection water in through the annular space outside the cone.
This forces the condensing water to take the shape of a hollow
cone into which the exhaust steam is discharged.
In the Knowles Spirojector condenser, which is otherwise simi-
lar to the Bulkley, the cone C has cast on its face vanes which
compel the injection water to assume a spiral or whirling motion
as it passes through the condenser to the discharge.
Fig. 11
HOT WELL
Arrangement of Injector Coridensor.
43
In Fig. 12 a pump is shown for lifting the condensing water; if
the level of the injection water supply is not more than, say, 20
RELIEF VALVE
feet below the condenser inlet, the condenser will siphon the water
over as soon as a vacuum is formed in it and the water pump may
44
The Injection Water Supply.
be dispensed with. As 20 feet is about the limit to which water
may be continuously lifted by the siphoning action, it follows
that when the water supply is more than 20 feet below the con-
denser a pump must be used. The arrangement with a pump
shown in Fig. 1 2 is sometimes modified by the insertion of a tank
(shown in dotted lines) at about the lower limit of the siphon.
This is convenient when a single-acting or single-cylinder tank
pump is used to lift the water; such a pump gives a more or less
intermittent flow, whereas a practically constant flow is required
by the condenser. In the tank arrangement, the pump discharges
intermittently into the tank and the condenser siphons continu-
ously from the tank. Fig.
13 shows the arrangement
of condenser and pipes for a
siphoning apparatus, when
no pump is used. In this
figure there is shown a
cross connection at the sup-
ply level between the injec-
tion and discharge pipes.
As we said before, the vac-
uum must be formed in the
condenser before it will
siphon water; by opening
the starting valve ^S water
is admitted to the discharge
pipe, and in falling through
the pipe it draws the air out
with it, forming enough
vacuum in the upper pipes
and condenser to draft the injection water up to the condenser. The
starting valve should then be closed and the water supply should
be regulated by valve J. When the injection supply is at the ex-
treme lower limit of the siphon, say 20 feet below the condenser,
this arrangement of starting valve is not always satisfactory; in
such cases the cross connection may be omitted and a small prim-
ing pipe P, shown in dotted lines in Fig. 13, may be run from the
boiler feed pump discharge to the condenser inlet. As soon as
the injection water appears the valve/ may be closed and the feed
Adva?itagcs of the Type.
45
RELIEF VALVE
pump may resume its usual duty. When a pump is used to ele-
vate the water, the starting valve or priming pipe and the injec-
tion valve/ are of course omitted, as the vacuum is formed by
forcing water directly into the condenser, and the water supply
is regulated by the pump speed.
This type of condenser is suitable for many locations, and if
properly made and connected will maintain a good vacuum. It is
economical in operation and has no moving parts to wear or to get
out of order. There is no way in which water can get into the
engine cylinder unless it is
allowed to accumulate in the
pocket formed by the ex-
haust pipe, and not even
then unless atmospheric
pressure is admitted to the
exhaust pipes through the
uncovering of the water
supply or discharge pipes.
A drain pipe placed as
shown in Fig. 12 will serve
to drain out the exhaust
pipe before the engine is
started and removes all
danger from this source.
Pumping action of the low
pressure cylinder cannot
draw water up from the hot
well on account of the
height, and water drawn
up from the injection supply would fall into the discharge pipe
and not into the exhaust pipe, by reason of the construction.
Another condenser of this type, but differing slightly from the
above in detail, is the Baragwanath water jacket condenser shown
in Fig. 14. In this condenser, as in the others, the exhaust en-
ters at the top and the injection at the side, and the exhaust noz-
zle is surrounded by cold water. The water chamber is larger
than in the others, and the shell of the condenser is prolonged in-
side the water chamber, forming an inverted cone, into the end of
which the condensing nozzle C projects. This nozzle is adjustable
46 Automatic Relief Valve.
by means of the spindle shown and can be set to admit precisely
the right amount of water.
Each of the three condensers mentioned herein, i. e., the Bulk-
ley injector, the Knowles Spirojector and the Baragwanath water
jacket, is supplied with an automatic atmospheric relief valve
similar to that shown in Fig. 13; this valve discharges directly
into the atmosphere, so that when the top of the condenser is in-
side the building it is necessary to use a relief valve in the pipe
line and to carry the atmospheric exhaust pipe out of doors. This
valve may be of the swinging check type shown in Fig. 3, or any
one of several well-known types. The injection water may be
supplied under a head or a pump of either the reciprocating, the
rotary or the centrifugal type may be used. The head against
which these pumps work is evidently quite small, since the
vacuum in the condenser will take care of the upper 18 or 20
feet of the lift.
THE EXHAUST STEAM INDUCTION CONDENSER.
The operation of this condenser is based upon the same principle
as that of the steam injector. As most of our readers know, the
operation of the injector is as follows: A jet of steam enters
through the steam tube at a high velocity and induces the air in
the suction pipe and injector body to pass out with it; this leaves
a vacuum and allows the atmospheric pressure to force in water.
The steam is condensed by this water and the velocity of the
steam is imparted to the water; then the energy in the moving
column of water is sufficient to overcome the pipe friction, lift
the check valve and force the water into the boiler against the
pressure.
An inspection of Fig. 15 shows that this is exactly the opera-
tion of the induction condenser. The exhaust steam enters
through the valve E and passes through the inclined perforations
into the central tube T, as shown by the arrows. Owing to the
velocity of its movement the air in the condenser and the injec-
tion pipe is drawn out with it, and the atmospheric pressure on
the injection supply forces the condensing water up through the
pipe and into the tube T as shown. The exhaust steam is con-
densed by this water and a vacuum is left in the condenser
and exhaust pipe. The original velocity with which the water
entered the condenser and the added velocity due to the
exhaust steam enable the mingled steam and water to over-
come the atmospheric pressure on the discharge end and
pass out into the hot well, just as the water from the injector
overcomes the resistance due to friction and pressure and passes
into the boiler. From this we see that the velocity of the dis-
charge is sufficient to draw out the air and to get rid of the con-
densing water and condensed steam; so that no air pump is re-
quired as in the case of a jet or surface condenser, nor a 34-foot
"tail" column, as in the injector or siphon condenser.
48
Arrajigement of Induction Co?ide?iser.
The condenser shown in Fig. 15, however, has its limits of
operation. We have just seen that the operation depends upon
the velocity of the discharge; it is plain that when the condenser
lifts its injection water, as shown in the figure, this velocity must be
almost wholly imparted by the exhaust steam. Then if the load
on the engine is variable or if the condenser is too large for the en-
gine, there will be times when the small amount of exhaust steam
QHI
Fig. 15.
furnished by the engine will not be enough to impart the required
velocity to the large volume of water and the condenser will not
operate satisfactorily. In other words, the volume of exhaust
steam must be, within limits, in proportion to the volume of
water which it keeps in motion, too little steam being unable to
induce the flow of water and too much steam affecting the vac-
uum. The minimum amount is that which will increase the
Adjusting the Capacity.
49
temperature of the water at least 300 F. and the maximum
amount is that which will not cause a rise of more than 500 F. in
the water temperature.
In cases where the condenser takes its water under a head, as
shown by dotted lines in Fig. 15, this objection does not apply,
for then the velocity of the water is that due to the head and is
independent of the exhaust steam.
In order to guard against the trouble due to a varying amount
of exhaust steam, the con-
denser shown in Fig. 16 has
been devised. It is called
the adjustable capacity con-
denser in order to distin-
guish it from the fixed
capacity condenser shown
in Fig. 15. Both the con-
densers shown were design-
ed by Korting and are
identified with 1^. Schutte
in America.
The adjustable condenser
shown in Fig. 16 is provid-
ed with a movable ram R
inside the central water
tube and a sleeve £ out-
side the tube. The ram is
tapering and controls the
volume of water admitted
by increasing or diminish-
ing the annular space be- ***,&*
tween its surface and the inside of the tube; while the sleeve 5,
by covering more or fewer openings in the tube, governs the area
of the exhaust inlet and consequently the velocity of the exhaust
steam. The relative positions of the ram and the sleeve can be
regulated by the extension rod K, so that the machine can be
adjusted for almost any condition of load. In fact, the machine
may be adjusted to work satisfactorily at any point from j{ or
1-5 of its capacity to full capacity; this is particularly desirable,
5<d Preventing Flooding.
as we have said, when the load is variable and the injection water
must be lifted. On the other hand, the range of the fixed ca-
pacity condenser is only from about one-half capacity to full ca-
pacity. For high suction lifts, the live steam jet or water pres-
sure jet/ is used to bring the water to the condenser, and an es-
cape is provided through the overflow valve O just as in the case
of the steam injector. This starting jet and overflow valve are
necessary only when starting, and may both be omitted when
the suction lift is very small or when water is supplied under a
head. It will be seen that in this condenser, as in the jet and
siphon condensers previously described, the condensed steam
and the condensing water are mixed together, so that the water
from the hot well can not be used for boiler feed unless the con-
densing water is pure. An inspection of Fig. 1 5 shows that an
atmospheric outlet must be provided for the exhaust, just as in the
cases of the jet, surface and siphon condensers. The figure shows
a special swing check valve for this purpose, while on the adjust-
able capacity condenser in Fig. 16 is shown the automatic valve
usually furnished with this type of condenser.
In this condenser there is no 34- foot tail column, and in case
the low pressure cylinder of the engine acts as a pump, water may
readily be drawn up into the engine.
This is prevented by the arrangement of the stop valve E,
through which the exhaust steam enters the condenser. The
valve itself is not fixed to the spindle, but is free to move verti-
cally within the limits set by the seat at the bottom and the collar
C on the spindle at the top. It thus allows steam to pass out
under it from the engine into the condenser, but acts as a check
valve against the passage of water in the opposite direction or
from the condenser to the engine. It may also be used as a stop
valve by lowering the spindle until the collar C locks the valve
to its seat. Since the seat of this valve is practically at the top
of the exhaust pipe, it is advisable to drip the pipe on the engine
side of the valve, as shown in Fig. 15, to prevent any accumula-
tion of condensation. This drip may be piped into the condenser
as shown, with a check valve arranged to prevent the return of
water from the condenser to the exhaust pipe.
The directions for starting or stopping au engine equipped with
either type of this condenser are very simple. It is always
Stopping and Starting with an Induction Condenser. 51
desirable to start the condenser and form the vacuum before
starting the ermine, as we have mentioned in connection with the
other condensers.
To start the engine, proceed as follows:
When the condensing water is under a head, turn on the con-
densing water and when a vacuum is formed start up the engine.
When the condensing water must be lifted, open the steam or
pressure jet valve/, and as soon as this has lifted the water start
the engine. The operation of the condenser will begin as soon as
the engine exhaust reaches the condenser and when the vacuum
is formed the suction or lifting jet may be turned off. In shutting
down, stop the engine first, when the operation of the condenser
will cease if the condensing water is under a suction lift; if the
water supply is under a head, stop the engine first and then shut
the valve in the water supply pipe.
52
CONDENSER CAPACITIES.
In column 4 of Table I are given the number of heat units
required to raise a pound of water from zero Fahrenheit to the
corresponding temperatures T in column 3.
In column 5 are given the numbers of so-called ' 'latent' ' heat
units L required to convert a pound of water at the corresponding
temperatures T into dry saturated steam of the same temperature,
the corresponding pressures being given in various units in columns
1 and 2.
Column 6 gives the total number of heat units H required to
raise a pound of water from zero F. to the corresponding temper-
ature and to convert it into steam of that temperature. It is the
sum of the corresponding values in columns 4 and 5.
For example, in a vacuum of 25 inches (column 1), wmich is
the same thing as an absolute pressure of 2.417 pounds to the
square inch (column 2), water vill boil at 133 degrees F. (column
3). It will take 133.21 heat units to raise a pound of water from
zero F. to this temperature (column 4), and 1,021.295 more heat
units (column 5) to evaporate the pound at that pressure and
temperature, making a total of 1,154.505 (column 6).
To make a pound of steam at an absolute pressure of 20 pounds
(column 2) from a pound of water at 1 io° would require
1,183.454—110.110 = 1,073.344
heat units, because the pound of water has already no. no heat
units in it (column 4) above what it would have at zero F. , and
there are in a pound of steam of 20 pounds pressure absolute
1,183.454 heat units above the number in a pound of water at
zero (column 6).
Condensation is the reverse of evaporation. If we wish to
TABLE I
i a I
-PHYSICAL PROPERTIES OP SFBAJI.
3 14 15 I
Heat Required
to Convert a Pound of Water
Pressure
Temperature.
at Zero F. into Steam.
Vacuum
To Raise the
To Conr<jrt the
„by
Absolute.
Temperature
Water at the
Total.
Gage.
to tho Boil-
Boiling Point
T
ing Point.
into Steam.
Inches
Lbs. per
h
L
H
Mercury.
.^q in.
Degrees F.
Heat Units.
Heat Units.
Heat Units.
29.74
.089
32
32
1091.700
1123.700
29.72
.100
35
35
1089.015
1124.615
29. G7
.122
40
40.001
1086.139
1126.140
29.6 J
.147
45
45.002
1082.661
1127.665
29.56
.170
50
50.003
1079.187
1129.190
29.49
.212
55
55.000
1075.709
1130.715
29.40
.254
GO
60.009
1072.231
1132.240
19.30
302
65
05.011
1068.751
1133.765
29.19
.359
70
70.020
10G5.270
1135.290
29
.425
75
75.027
1061.788
1136.815
28.90
.502
80
80.030
1058.304
1138.340
28.72
.590
85
85.045
1054.8 0
1139.&65
28.51
.692
90
90.055
1051.355
) 141. 390
23.27
.809
95
95.0G5
1047.850
1142.915
28
.943
100
100.080
1044.300
1144.440
27 85
1.
102
102.086
1042.9C4
1145.050
27.09
1.094
105
105.095
1040.870
1145.965
27.34
1.205
110
110.110
1037.380
1147.490
27
1.435
114.34
114.470
1034.344
1148.814
26.95
1.462
115
115.129
1033.880
1149.015
26.50
1.682
120
120.149
1030.391
1150. 54J
26
1.931
125
125.169
1026.896
1152.0b5
25.85
2.
126.266
126.440
1026.010
1152.450
25.42
2.213
130
130.192
1023.389
1153.590
25
2.417
i:53
133.21
1021.295
1154.505
24.79
2.520
135
135.217
1019.898
1155.115
24. GO
2.876
140
140.245
1016.305
1156.640
24
2.9
141.293
141 .543
1015.491
1157.034
23 81
3.
141.622
141.877
1015.254
1157.131
23 26
3 270
145
145.275
1012.890
1153.165
23
3.399
146.528
146.808
1011.823
1158.631
22 37
3.707
150
150.305
1009.385
11:9.690
22
3.9
152.0")
152.37
1007.945
1160.315
21 73
4
153.070
153.396
1007.229
1160.625
21 39
4.' 191
155
155.339
1005.876
1161.215
21
4 373
156.74
157.09
1004.452
1161.542
20.29
4.729
1G0
160.374
1002.366
1162.740
20
4.S63
]61. 63
161.543
1001.552
1163.095
19 74
5.
1G2.33
162.722
1000.727
1103.449
19 08
5.324
163
105.413
998.852
1161.265
19
5.30
105.317
105.730
998.632
1164.362
n
5.855
109
169.45
990.035
1165.485
17.74
5.981
170
170.453
9)5.337
1165.790
17.71
c.
170.123
170.577
995.249
1165.826
17
6.346
172.6
173.07
993.513
1166.583
lrf.27
6.704
175
175 497
991.818
1167.315
1G
6.837
175.9
176.4
991 . 180
1167.580
15 67
7.
176.910
177.425
990.471
1167.896
15
7.329
178.98
179.51
989.019
1163.529
14 65
7.500
180
180.542
988.298
1168.840
14
7.82
181.877
182.427
086.980
1169.407
13 63
8.
182.910
183.481
986.245
1169.726
13
8.311
184.668
185.25
985.014
1170.204
12 87
8 :-75
185
185.591
984.774
1170.365
ia
8 802
187.272
187.885
933.360
1171.245
11. GO
9.
183.316
1S8.941
932.434
1171.375
11
9.293
189.82
190.46
981.375
1171.835
10 92
9.33
190
190.613
981. 047
1171.890
10
9.784
192.21
192.89
979.674
1172.561
9.56
10.
193. *40
193.919
978.958
1172.877
0
10.275
194.53
195.22
978.052
1173.272
8.79
10.33
195
195. 6&7
977.713
1173.415
8
10.767
196.742
197.46
976.480
1173.946
7.53
1..
197.768
198.496
075 762
1174.258
7
11.253
198 9
199. C4
974.964
1174. 6"4
6.46
11.52
200
200.753
974.167
1 174 940
54
Heat in a Pound of Steam.
6
r n.7
6.49
12.
5
12.24
4
12.73
3.93
12.766
3.45
13.
3
13.222
2
13.714
1.42
14.
1.17
14.122
1
14.205
14.G96
Gage
Pressure
lbs. per
gq. inch.
.304
15
1.304
1<S
2.304
17
3.304
18
4.304
19
6.304
20
6.304
21
7.304
22
8.801
23
9.304
24
10.304
25
11.304
26
12.304
27
13.304
28
14.304
29
15.3J4
30
200.747
201.514
973.654
1175.168
201.960
202.737
972.800
1175.537
202.924
203.712
972.120
1175.832
'204.772
205.58
970.815
1176.395
£05
205.813
970.652
1176.465
205.88-)
206.109
970.025
1176.734
206.722
207.557
969.453
1176.99
208.522
209.377
968.162
1177.539
209.560
210.428
967.427
1177.855
210
210.874
967. 11G
1177.990
210.3
211.17
966.9115
1178.0815
212
212.900
965. 7C0
1178.600
213.025
213.939
9G4 973
1178.912
216.296
217.252
962.657
1179 909
219.410
2C0.409
D60.450
1180.859
222.378
223.419
958.345
1181.764
225.203
226.285
956.343
1 182 . 628
227.917
229.0 9
954.4 5
1183.454
230.515
231.676
952.570
1184.246
233.017
234.218
950.791
1185.009
235.432
236.672
949.072
1185.744
237.752
239.029
947.424
1186.453
240.000
241.314
945.825
1187.139
242.175
243.526
944.277
1187.803
244.281
245.671
942.775
1188.446
246 326
247.748
941.321
1189.069
248.310
249.769
9^9.905
1189.674
250.245
251.738
838.925
1190.263
reduce a pound of steam at an absolute pressure of 20 pounds to
water at 1 io° we shall have to take out of it
1,183.554—110.110= 1,073.344
heat units, because the pound of steam contains 1,183.454 units,
of which 1 10 1 10 will remain in the water, always reckoning from
zero Fahrenheit.
It will be seen by comparing columns 3 and 4 that the heat in
the water is very nearly the same as the temperature of the water,
the increase on account of the greater specific heat at higher
temperatures being less than one heat unit between 32 ° and 2120.
It will be sufficiently accurate for our purpose to consider the
heat in the water the same as the temperature, i. e.} to consider
column 4 equal to column 3, letting a heat unit represent the
amount of heat necessary to raise a pound of water one degree
irrespective of the temperature.
If we represent by t the temperature at which the injection or
circulating water comes to the condenser and by T the tempera-
ture at which it leaves, the number of heat units absorbed by
each pound will be approximately
T—t.
The number of heat units to be taken out of a pound of steam
to condense it is, as we have seen above,
H—h,
Water Required to Condense a Pou?id of Steam. 55
i. e. , the total heat in the steam less the heat in the resulting
water.
By dividing the number of heat units to be abstracted by the
number absorbed by each pound of condensing water we find
the quantity, Q, of water required to condense a pound of steam
Where H = the total heat in a pound of steam of the given
pressure,
h = the heat in a pound of water at the temperature of
the condensed steam,
t= the temperature at which the condensing water
enters the cor denser,
T= the temperature at which the condensing water
leaves the condenser.
TO FIND THE AMOUNT OF WATER REQUIRED TO CONDENSE ONE
POUND OF STEAM.
Rule: — From the total heat in one pound of steam of the given
pressure subtract the heat i?i one pound of water at the condenser
temperature. Divide the remainder by the rise in temperature of
the injection or circulating water in passing through the condenser.
The quotient will be the number of pounds of water required to con-
dense one pound of steam.
In considering the condensation of steam in an engine the value
of H must be taken at the terminal pressure., not at the counter-
pressure or vacuum line. The engine delivers the steam to the
condenser at the pressure existing at the point of release, and if
the steam were dry saturated each pound would carry to the
condenser the number of heat units given in column 6 of Table I.
There is, however, little difference in this value for the entire
range of terminal pressures met with in good practice, and the
quality of the steam may vary widely. There is little use strain-
ing after extreme accuracy in this particular, and we shall be
entirely safe for the average case and not far from right in any
case if we assign to H the maximum probable value of 1,190,
corresponding closely to a terminal pressure of 30 pounds absolute.
Call the temperature of the air pump discharge r, which, allow-
ing one heat unit per degree of temperature, would equal h.
Substituting these values for H and h in formula 1 we have
56
To Find Quantity of Water Required
1 1 90 — T
T—t
(2)
APPROXIMATE RULE FOR THE QUANTITY OF CONDENSING WATER
REQUIRED PER POUND OF STEAM CONDENSED.
Rule: — Subtract the temperature of the air pump discharge from
1, 1 go and divide the remainder by the rise in temperature of the
condensi?ig water.
Table II has been computed by this formula and gives the
values of Q, i. e. , the pounds of water required to condense a
pound of steam for condenser temperatures of from 90 to 130 and
with from 5 to 90 degrees of difference in the condensing water.
In a jet condenser where the condensing water is mingled with
TABLE II.— POUNDS OF WATER REQUIRED TO CONDENSE ONE POUND OF STEAM.
1190— r
Q =
T
-t
T-t
Temperature of air pump discharge.
r
90
95
100
102
104
106
108
110
112
114
116
118 j
120 |
125
130
5
220
219
218
217.6
217.2
216.8
216 4
216
215.6
215.2
214.8
214.4
214
213
212
10
110
109.5
109
108.8
108.6
108.4
108.2
108
107.8
107. 6
107.4
107.2
107
106.5
106
15
73.3
73
72.7
72.5
72.4
72.3
72.1
72
71.9
71.7
71.6
71.5
71. 31
71
70.7
20
55
54.7
54.5
54.4
54.3
54.2
54.1
54
5J.9
53.8
53.7
53.6
53.5
53.2
53
25
44
43.8
43. .
43.5
43.4
43.4
43.3
43.2
43.1
43
42.9
42.9
42.8)
42.6
42.4
30
36.7
36.5
36.3
36.3
,c6.2
36.2
36.1
36
35.9
35.9
35.8
35.7
35.7
35.5
35.3
3)
31.4
31.3
31.1
31.1
31.0
31
30.9
30.8
30.8
30.7
• 0.7
30.6
30.5
30.4
30?
40
27.5
27.4
27.2
27.2
27.1
27.1
'27
27
26.9
26.9
26.8
'26.8
26.7
26.6
26.5
45
24.4
24.3
24.2
24.2
24.1
24.1
24
24
23.9
23.9
23.9
23.8
23.8
23.7
23 5
50
22
21.9
21.8
21.8
21.7
21.7
21.6
21.6
21.6
21.5
21.5
21.4
21.4
21.3
21.2
55
20
19.9
19.8
19.8
19.7
19.7
19.7
19.6
19.6
19.6
19.5
19. 5j
19.4
19.4
19. S
60
18.3
18.2
18.2
18.1
18.1
18.1
18
18
18
17.9
17.9
17 9
17.8
17.7
17 7
G5
16.9
16.8
16.8
16.7
16.7
16.7
16.6
16.6
16.6
16.5
16.5
16.5
16.5
16.4
16.3
70
15.7
15.6
15.6
15.5
15.5
15.5
15.4
15.4
15.4
15.4
15.3
15.3
15.3!
15.2
15.1
75
14.7
14.6
14.5
14.5
14.5
14.4
14.4
14.4
11.4
14 3
14.3
14.3
14.3!
14.2
14.1
80
13.7
13.6
13,6
13,6
13,6
13.5
13.5
13.5
13.5
13.4
13.4
13 4
13.41
13.3
13.2
85
12,9
12.8
12.8
12,8
12,8
12.7
12.7
12.7
12 7
12.6
12.6
12.6
12.6
12.5
12.5
90
12 2
12.2
12.1
12.1
12.1
19
12
12
12
11.9
11.9
11.9
11.9
11.8
11.8
the steam T and r become identical and formula becomes
a — IT9°— T
V T—t
Table III has been computed by this formula and gives the
value of Q, i. e., the number of pounds of injection water required
per pound of steam with the injection water from 35 to 100
degrees and the air pump discharge from 900 to 1400.
SIZE OF AIR PUMP FOR JET CONDENSER.
If we designate by H^the weight of steam to be condensed per
hour, the number of pounds of water to be handled per hour by
the pump will be
W(Q+i).
Displacement Required for Water.
0/
For example, if we had a ioo horse power engine using 20
pounds of steam per hour per horse power the weight JVoi steam
to be condensed per hour would be 20 X 100= 2,000 pounds. If
it takes 20 pounds of water to condense a pound of steam, then
for each pound of steam condensed we shall have
20 -f- 1 pounds
of water to pump, 20 pounds of injection and one pound of con-
densed steam. For 2,000 pounds we shall have
W (g-f 1) = 2,000(20+ 1).
XARLE III.
a,
® * 2
£ 3(1|
E-t ° w
92
91
96
98
100
102
104
106
108
110
112
114
116
118
120
122
124
126
128
130
132
134
136
138
140
-POUNDS OF INJECTION WATER .REQUIRED PER POUND OF
STEAM CONDENSED.
Entering Temperature of Injection Water t.
3j 40 45 50 55 GO 65 70 75
90 95 100
I I
Pound.3 of Condensing Water Required per Pound of Steam. Q =
1190— T
T—t
20 0
19.2
18 6
17.9
17 3
16.8
16.2
15.7
15.3
14.8
14.4
14.0
13.6
13.3
12.9
12.6
12.3
12.0
11.7
11.4
11.2
10.9
10.7
10.4
10.2
10.0
»0
24.4
21.1
23.4
20 3
22.4
19.5
21.4
18.8
20.6
18.2
19.8
17.5
19.1
17.0
18.4
16.4
17.8
15.9
17.2
15.4
16.6
15.0
16.1
14 5
15.6
14.1
15.1
13.7
14.7
13.4
14.3
13.0
13.9
12.7
13.5
12.4
13.1
12.1
12.8
11.8
12.5
11.5
12.2
11.2
11.9
11.0
11.6
10.7
11.3
10.5
11.1
27.5
26.1
24 9
23.6
22.7
21.8
20.9
20.1
19.4
18.7
18.0
17.4
16.8
16.3
15.8
15.3
14.8
14.4
14.0
13.6
13.2
12.9
12.6
12.3
12.0
11.7
31.4
36.7
29.7
34.3
28.1
32.2
26.7
30.4
25 4
28 7
24.2
27.2
23.1
25.9
21.2
24.7
21.3
23.6
20.4
22.5
19.6
21.6
18.9
20.7
18.2
19 9
17.6
19.2
17.0
18.5
16.5
17.8
15.9
IT. 2
15.4
16.7
15.0
16.1
14.5
15.6
14.1
15.1
13.7
14.7
13 4
14.3
13.0
13.9
12.7
13.5
12 4
13.1
44.0
40.7
37.8
35.3
30.1
31.1
29.4
27.8
26.4
25.2
24.0
22.9
42.0
21.1
20.2
19.5
18.7
18.1
17.4
16 9
16.3
15.7
15.3
14.8
14.4
14.0
55.0
49.9
45.7
42.1
39.0
36.3
34.0
31.9
30.1
28.5
27.0
25.7
24.5
23.3
22.3
21.4
20.5
19.7
19.0
18 3
17.7
17.1
16.5
16.0
15.5
15.0
73 3
64.6
57.7
52.1
47.5
43.6
40.3
37.4
35.0
32.8
30.9
29.1
27.6
26.2
24.9
23.8
22.7
21.8
20.9
20.0
19.3
18.6
17.9
17.3
16.7
16.2
110.0
91.5
78 1
68.4
60.7
54.5
49.5
45.2
41.7
38.6
36.0
33.6
31.6
29.8
28.2
26.7
25.4
24.2
23.1
22.1
21.2
20.3
19.6
IS. 8
18.1
17.5
220.0
156.8
121.8
99.4
84.0
72.7
64.0
57.2
51.6
47.0
43.2
39.9
37.1
34.6
32.5
30.6
28.9
27.3
26.0
24.7
23.6
22 5
21.6
20.7
19.8
19.1
549.0
274 .-0
182.3
136.5
109.0
90.7
77.6
G7.7
G0.1
51.0
49.0
44.8
41.3
38 3
35.7
33.4
31.4
29.6
27.9
26.5
25.2
24.0
22.9
21.9
21.0
364.0
218.0
155.4
120.7
98.5
83.2
72.0
63 4
56.6
51.1
46.6
42.8
39.6
36.8
34.3
32.2
30.3
28.6
27.1
25.7
24.5
23.3
544.0
271.5
180.7
135.2
1084)
89.8
76.9
67.1
59.6
53.5
48.5
44.4
40.9
37.9
35.3
33.1
31.0
29.2
27.7
26.2
It takes in round numbers 28 cubic inches to make a pound of
water at ordinary condenser temperatures, so that if we multiply
this by 28 we shall get the number of cubic inches of water to be
pumped per hour. By dividing this by 60 we get the number of
cubic inches to be pumped per minute, and our formula so far
becomes
Water pumped per minute=
28
W (04- 1) ^-cubic incheSc
v 60
58 Additional Displacement for Air.
But in addition to the water we have a considerable quantity of
air to handle, and we cannot count upon an efficiency of ioo per
cent, so we must provide a pump of a displacement considerably
more than the volume of the water. I,et us call the ratio of the
pump displacement to the volume of the water R. For instance,
if the displacement were twice the volume of the water or the
pump were allowed to half fill with water, R would be 2. Then
the pump displacement D in cubic inches per minute would be
If there is any standard value for R, if we can determine what
proportion of their displacement it is safe or advisable to allow
pumps of the different types to fill, we can combine this standard
28
value of R with the fraction ~^~ into a coefficient K and the
formula becomes
D = KW{Q+i). (3)
For instance suppose it was the usual practice to use a pump
having a displacement of twice the volume of the water to be
pumped, i. e., to let the pump fill half full of water, then R
Vould equal 2, and
60 60 ^
andZ)=.93 W(Q+i).
Table IV gives the values of K for various values of R. If
the pump fills with water to 60 per cent, of its displacement
(column 1), i. e.y if the displacement is 1.667 times the volume
of the water (column 2), the value of A'wouldbe .78 (column 3).
In order to establish the values of K used in current practice
with various kinds of pumps we have obtained from such manu-
facturers as were willing to furnish them the data contained in
Tables V to XIII. From the data in columns 2 to 6 the displace-
ment D in cubic inches per minute has been computed, corrected
for the rod, when its diameter (column 3) was known. Columns
9 and 10 give the value of Wy i. e.} the weight of steam con-
densed per hour which the pump is adapted to take care of by the
builder's rating. The values in column 10 are all reduced to 20
pounds of injection water to 1 of steam. When the builder's
rating is based upon a different value of Q it is to be found in
column 8. In columns 13 and 14 are the values of A" correspond-
To Find Size of Air Pump,
59
ing with the ratings for jet and surface condensers respectively.
Take, for example, the Conover vertical single acting air pump,
Table V. For a jet condenser the value of K for everything but
the smallest size is .75 (column 13). In column n is given the
capacity computed by the formula as given at the head of the
column, which is simply a transposition of formula 3, taking K
= . 75 and the values
there given will be seen
to run very close to the
builder's rating.
Knowing the value of
K the process becomes
very simple. Suppose
we have a 500 horse
power engine using 20
pounds of steam per hour
per horse power; that
the temperature of the
injection water will be
for considerable periods
as high as 65 °, and we
want to keep the hot well
or condenser temperature
down to no°. What
size Conover pump
should we require ? We
see from Table III that
it will take 24 pounds of
injection water per pound
of steam; then
Q= 24;
jv= 500 x 20 = 10,-
000;
TABLE IV. -VALUES OF K FOR
DIFFERENT
RATIOS OF DISPLACEMENT TO VOLUME
OF
WATER HANDLED
1
2
3
Per cent of Air
Ratio of Air
Pump Dis-
Pump Displace-
Value
placement Filled
ment to Volume
of
with Water.
of Water.
K.
V
D
28
100 —
R = —
K = -R
D
V
60
Surface.
5
20
9.33
5.26
19
8.87
5.56
18
8.40
5.88
17
8.00
6.26
16
7.47
6.66
15
7
7.14
14
6.P3
7.69
13
6.07
8.33
12
5.60
9.09
11
6.13
10.00
10
4.67
Jet.
33.33
3
1.4
35
2.941
1.33
36
2.778
1.30
38
2.632
1.23
40
2.5
1.17
42
2.381
1.11
44
2.273 .
1.07
46
2.174
1.02
47
2.143
1
48
2.083
.97
50
2
.93
52
1.923
.90
54
1.852
.86
56
1.786
.83
58
1.724
.80
60
1.667
.78
62
1.613
.75
64
1.5*2
.73
66
1.515
.71
66.67
1.5
.70
68
1.471
.69
70
1.429
.67
72
1.389
.65
74
1.351
.63
75
1.333
.62
76
1.316
.61
78
1.282
.GO
80
1 250
.58
75;
K
and
D= K W (Q -f- 1) = .75 X 10,000 X 25 = 187,500 cu. in.
per min.
The sizes nearest to this capacity are the numbers 1 1 and 1 2
60 To Find Size of Air Pump.
(which, by the way, have the same size of air cylinder but differ-
ent steam cylinders), having a capacity of 158,340, and the
numbers 13 and 14, with a capacity of 204,781 cubic inches per
minute. The purchaser can determine if it is safe in his case to
take the next smaller or whether the next larger is necessary.
For the double-acting horizontal pumps the value of K runs
very close to unity in several of the tables, although some of the
makers rate them so high as to bring K down to a figure which
gives them a considerably greater efficiency than the vertical
single-acting pumps. What incongruities there are in the columns
of K are evidently due to erratic ratings, for there should be no
reason why one pump of the same kind and make should have a
greater displacement per pound of water handled than the size
next to it, saving always that very small sizes may be less efficient
than the larger. Where the diameter of the rod is not given
there would be a greater proportional difference between the net
and gross displacement in the smaller sizes, which would call for
a larger value of K for a very small pump where the displace-
ment is uncorrected for the rod. As for the difference in the
values of K as given by the ratings of the different makers we
must leave our readers to judge whether there should be so much
difference in the efficiency of the respective pumps that one could
be allowed to fill over 78 per cent. , while the other fills less than
50 per cent, of the stroke.
From the data presented the conclusion would appear warranted
that a safe value for K would be .75 for vertical single-acting
pumps and unity for horizontal double-acting pumps, and that
pumps selected by the following formulas would be very close to
what the makers would recommend for the capacity required:
For horizontal double- acting pumps: —
D= W(Q+t) (4)
For vertical singlk-acting pumps: —
Z>=.75 1V(Q+i) (5)
to determine the size of air pump required for a jet
condenser.
RULE: — Multiply the number of pounds of steam to be condensed
per hour by one plus the number of pounds of injection water ?r-
quired per pound of steam. The product will be the required pump
How Pumps Should be Rated. 6r
displacement in cubic indies per minute for a horizontal double-
acting pump. For a single-acting vertical pump multiply the
above product by .75.
In column 1 1 of the tables are given the capacities calculated
by formula 4 or 5, according to the type of pump. In all except-
ing a few instances of abnormally high rating the capacities will
be seen to agree substantially with the rated capacities of the
builders in column 9.
We are informed by one of the makers that they find the long
rating perfectly safe, because they always use the size next above
the required' computed capacity. For instance, Dean Bros, rate
their 7X I2 X I2 at 5,535 pounds of steam per hour, with 26
pounds of injection to one of steam, which gives a value for K of
.632. This requires the pump to fill with water to almost 74 per
cent, of its volume (Table IV), a condition which could not be
counted upon to preserve a good vacuum with a double-acting
horizontal pump, but this pump is used for everything between
2,300 and 5,500. With a capacity of about 2,950 its coefficient
becomes unity and its capacity ample. Much of the time, too,
the temperature of the injection would be such that less than 26
pounds of injection would be used, and it is improbable that the
maximum conditions of load and injection temperature will come
together. On a pinch, too, the speed of the pump could be
increased above that given in columns 5 and 6. We think, how-
ever, that the pump should be rated at what it will do continu-
ously and comfortably under the given conditions, and the
engineer be allowed to decide how much he wishes to exceed that
capacity in the maximum demand which he is likely to put upon
it. The reduction of the ratings to a common unit of K= 1 for
horizontal double-acting pumps and K= .75 for single-acting
vertical pumps (column 11) makes this possible and easy. It
should be noticed that this column is computed for 20 pounds of
injection to one of steam.
In selecting a pump, it should be remembered that the work
done depends upon the volume of air and water delivered against
the atmospheric pressure, and not upon the size of the pump. In
Fig. 4, which is a section of the Conover single-acting pump,
suppose the volume of air and water in the chamber B to be so
small that the air would not be compressed enough to lift the head
62
Work Performed by Air Pump.
valves. On the upward stroke the pump performs the work of
lifting the water resting on the piston and of compressing the air.
On the downward stroke the water, in descending, gives back
the work required to lift it, and the air in expanding the work
required to compress it, so that no work is done except that
required to overcome friction. When the volume of air and water
in B becomes so great that the head valves are lifted the remainder
of the stroke is completed against the pressure of the atmosphere,
and the work done is proportional to the volume of air and water
Fig. 4.
delivered at atmospheric pressure. Aside, then, from the
additional investment in and friction of the larger pump, it is at
no disadvantage over the smaller.
In computing the displacement of a single-acting pump, it
should be noted that when a foot- valve is used, the pump is to
an extent double acting. This will be seen by reference to Figs.
Single Acting Pump with Foot Valve is Double Acti?ig. 63
2 and 3. When the piston is in its highest position, as in Fig. 2,
we have the volume between the head and the foot valves con-
taining only the piston. When the piston is in its lowest position
(Fig. 3) this volume has been further reduced by the volume of
the trunk, and a volume equal to the cross sectional area of the
trunk, multiplied by the
length of the stroke, must I Fig 2 Fig. 3.
have been discharged i|||||
through the head valves on
the downward stroke.
When the area of the trunk
becomes equal to that of
the annular space around it,
the pump discharges as
much on the downward as
upon the upward stroke. Where no foot-valve is used, as in
Fig. 1, the water is held against the piston by the head at Ay
avoiding the disagreeable chug which occurs when the piston is
allowed to come against a confined body of water.
The factor of uncertainty in air pump work is the air entering
by leakage. This air
entering at the atmospheric
pressure of. say, 15 pounds,
I expands in a vacuum of 26
I inches to over 7 times its
£ original volume, and this
I increased volume must be
I provided for in the displace-
3 ment of the air cylinder.
This factor is therefore an
exceedingly important one,
4 and is very variable. Some
plants are tight, others are
no eixT«F
BY ICflK/VGE
JNDENSING WATER
-2O-V0LuMtS-
£4 VOLUMES
5<> W.JLUME
Fig.
not. Generally plants using a small amount of steam per horse
power have a large leakage factor, because while the amount of
steam used per horse power is decreased, the leakage is liable to
go the other way, the pressure in the lower pressure cylinder be-
ing much of the time below that of the atmosphere.
64 Size of Air Pump for Surface Condenser.
SIZE OF AIR PUMP FOR SURFACE CONDENSER.
In a jet condenser, the air pump has to handle a comparatively
large amount of water. In the surface condenser it handles a
small volume of water and a large volume of air. Assume 20
pounds of injeccion to one of steam condensed, air carried by the
water one- third the volume of the water when expanded, and an
air pump with a displacement about two and a half times the
volume of the water to be moved. Under these conditions we
should have in Fig. 1 :
At A the condensed steam = 1 vol.
At B the condensing water = 20 vols.
At Cthe air entering with the water = 7 vols.
And at D the space which it is found necessary to provide for
the air entering by leakage and to cover the deficiencies of the
pump, consisting of 24 volumes.
In a surface condenser we have to handle only the water
represented by A. The space B, therefore, can be cut out of the
diagram, as can also the space C, as the only water which can
bring in air is the comparatively small quantity used for make-up.
We are liable to have as much air enter by leakage into a surface
as into a jet system, so that the portion of the space D which is
required for air entering by leakage, and this is the greater por-
tion of it, will remain unchanged. The portion required to cover
the lack of perfection in the pump will diminish with the volume
pumped. With a pump of half the size a less number of cubic
inches of volume will be lost by failure to fill, slippage, failure of
valves to seat, etc.
If D were left as it is, we should have a displacement 25 times
the volume of the water pumped. The practice of the pump
companies generally is to give the air pump a displacement equal
to 20 times the volume of the condensed steam, if it is a horizontal
double-acting, and 1 2 times if it is vertical single-acting. The
Conover company give their pumps a displacement of only 10
times the volume of the condensed steam.
The values of A" for these ratios are:
R K
10 = 4.67
12 = 5.6
20 = 9-33
Air Pump for Surface Condenser. 65
For general use these values may safely be taken at 9 for a
horizontal double-acting, and at 5 for a vertical single-acting
pump. Since there is no injection the volume of water to be
handled is simply W, and the formulas become:
For a horizontal double-acting pump
D = 9W (6)
For a vertical single-acting pump
B = 5W (7)
or generally
D = KW (8)
TO DETERMINE THE SIZE OF AIR PUMP REQUIRED FOR A SURFACE
CONDENSER.
Multiply the number of pounds of steam to be condensed per hour
by 9 for a horizontal double-acting or by 5 for a vertical single-
acting pump. The product will be the air pump displacement
required in cubic inches per minute.
In column 1 2 of the tables are given the capacities calculated
by formula 6 or 7, according to the type of pump. A comparison
between columns 10 and 12 will show how nearly the formula
with the constants chosen will come to the builder's rating. Of
course the general formula 8 may be employed, the user choosing
his own value of K.
CONDENSING SURFACE REQUIRED.
In the early days of the surface condenser it was thought
necessary to provide a cooling surface in the condenser equal to
the heating surface in the boilers, the idea being that it would
take as much surface to transfer the heat from a pound of steam
to the cooling water and condense the steam as it would to
transfer the heat from the hot gases to the water in the boiler and
convert it to steam. The difference in temperature, too, between
the hot gases and the water in the boiler is considerably greater
than that between the steam in the condenser and the cooling
water. Steam, however, gives up its heat to a relatively cool
surface much more readily than do the hot furnace gases, and the
positively circulated cooling water takes up that heat and keeps
the temperature of the surfaces down, while in a boiler the
absorption depends in a great measure upon the ability of the
water by natural circulation to get into contact with the surface
66 Cooling Surface in Surface Condensers.
and take up the heat by evaporization. It has been found, there-
fore, that a much smaller surface will suffice in a condenser than
in the boilers which it serves.
The Wheeler Condenser and Engineering Company, who make
a specialty of surface condensers, say that one square foot of
cooling surface is usually allowed to each 10 pounds of steam to
be condensed per hour, with the condensing water at a normal
temperature not exceeding 75 °. This figure seems to be gener-
ally used for average conditions. Special cases require special
treatment. For service in the tropics the heating surface should
be at least ten per cent, greater than this estimate: Where there
is an abundance of circulating water the surface may be much
less, as with a keel condenser, where 50 pounds of steam is some-
times condensed per hour per square foot of surface; or a water
works engine, where all the water pumped is discharged through
the condenser and not appreciably raised in temperature, probably
condensing 20 to 40 pounds per hour per square foot of surface.
Mr. J. M. Whitham, in a paper upon "Surface Condensers,"
presented to the American Society of Mechanical Engineers,*
gives the following formula for calculating the surface required:
C— WL
180 ( T—.t)
Where
S-= the surface in square feet,
W= the weight of steam condensed per hour,
L = the latent heat of steam at the condenser temperature,
T= the temperature of the condenser, or the air pump dis-
charge,
and / = the average temperature of the circulating water, i. e. , the
sum of its initial and final temperatures, divided by 2.
For ordinary conditions this reduces to
o 17 W
*~ 180
or one square foot of heating surface to about 10.6 pounds of steam
condensed per hour.
This refers to the ordinary arrangement of horizontal brass
tubes of small diameter to the surface condenser as ordinarily
*See Trans. A S. M. E., Vol. IX, p, 417.
Size of Injectiori Main. 67
used. With other arrangements of surface, etc., it might not
apply.
CONDENSING WATER PER HORSE POWER IN GALLONS.
The value of Q can be reduced to gallons by dividing by 8.25,
for since one pound equals 28 cubic inches one pound equals
2M=^250fagall0n-
If we let S = the steam required per horse power per hour, the
weight of steam to be condensed per hour for a given engine will be
W=/fPXS
The condensing water required in pounds per hour will be
WQ = //PXQXS
in gallons per hour,
JfPXQXS
8.25
or, in gallons per minute,
HPXQXS ^HPXQXS
60X8.25 495
0 s
This is gallons per minute per horse power.
Taking 20 pounds of steam per horse power per hour and 25
pounds of condensing water per pound of steam the condensing
water per horse power =
— — ass - — gals, per min.,
495 495
or just about a gallon per minute per horse power, which is a
a much used value.
SIZE OF INJECTION MAIN.
The injection main should be so proportioned that the velocity
of flow does not exceed 300 feet per minute, a velocity which will
be closely approximated by making the diameter of the pipe the
square root of the quotient of the pounds of condensing water
required per hour divided by 6,000.
For examp1e. to condense 2,000 pounds of steam per hour with
24 pounds of injection per pound of steam would require
24 X 2,000 = 48,000 pounds of injection water per hour.
Divide this by 6,000 and extract the square root and you have
the pipe diameter,
48,000 -f- 6,000 = 8
68 Relation of Temperature and Vacuum
The pipe should evidently be 3 inches, the square of 2.5, the
next lower size being 6.25.
If there were no air present in the condenser the temperature
for a given vacuum or absolute pressure would be that given in
Table 1. There is in the condenser, however, the pressure not
only of the steam arising from the water, but that of the enclosed
air, so that for a given condenser temperature the absolute
pressure will be higher, i. e. , the vacuum will be less than in-
dicated by the table. With a temperature of air pump discharge
of 1200, for instance, we should have, if there were nothing pres-
ent but the water and the steam arising from it, an absolute
pressure of 1.682 pounds per square inch, or a vacuum of 26.5
inches. We cannot have a lower absolute pressure, i. e.y a better
vacuum, with this temperature, because the water at this temper-
ature will continue to give off steam of this pressure and keep the
condenser full of it, no matter how much capacity wre have to our
air pump. Now, if we admit a little air we shall have an
additional pressure with no increase of temperature, and of course
there will be some air present. For this reason it is common to
see condensers running with a discharge temperature of ioo°,
which by the table should give a vacuum of over 28 inches, with
the gage showing 26 or less.
69
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78
INDEX.
B
/\bsolute Pressure, 9.
Air and Circulating Pumps driven by
motors, 40.
Air-Pump for Surface Condenser, 65.
Air-Pump ; location of, 27.
Air-Pump rating, 61.
Air-Pump ; To find size of, 59-60.
Air-Pump ; Total work of, 62.
Air- Pump ; Types of, 39.
Air-Pump Valves ; lifting or clattering of,
27.
Air-Pump ; Vertical, 22.
Air; Pumping, 10.
Area of Cooling Surface in Surface Con-
denser, 65-66.
Atmosphere ; Pressure of the, 3.
arr Horizontal Double-Acting Pumps ;
Table of, 77.
Capacity of a Condenser ; To calculate
the, 65-68.
Circulating Pump, 39-40.
Cooling Surface of a Surface Condenser,
65-66.
Cooling Towers, 26
Cooling Water required for condensing,
15. 16, 55-57, 67.
Condensation in a Cylinder, 18-19
Condensation ; Production of a vacuum by
means of, 11.
Condenser Capacity, 52-68
Condenser ; Induction See Induction Con-
denser.
Condenser; Injector. See Injector Con-
denser ,
Condenser ; Jet. See Jet Condenser
Condenser; Siphon See Injector Con-
denser,
Condenser; Surface See Surface Con-
denser
Condenser unavailable, 17
Condensers ; Independent and direct-
driven, 21.
Condensing by Evaporation, 26.
Condensing Engine ; How to start and stop
a, 33. 35, 5i-
Condensing; Gain due to, 12-14.
Condensing , L,oss in temperature of feed-
water due to, 14.
Condensing ; Water required for, 15, 16,
55-57. 67
Condensing Water per Horsepower, in
gallons, 67.
Condensing Water ; Pump displacement
required for, 57.
Conover Vertical Single-Acting Pumps ;
Table of, 69.
Cylinder Condensation, 18-19.
^J iagram of Maximum Efficiency, 20.
Dean Bros.' Horizontal Double-Acting
Pumps, Table of, 70.
Dean Bros. ' Twin Cylinder Vertical Single-
Acting Pumps ; Table of, 76.
Deane Horizontal Double-Acting Pumps ;
Table of, 75.
^^fficiency ; Diagram of maximum, 20.
Engine Equipped with Independent Jet
Condenser ; Stopping an, 35.
Engine equipped with Induction Condenser;
Stopping and starting an, 51.
Engine equipped with Jet Condenser;
Starting and stopping an, 33, 35.
Evaporation ; Condensing by means of, 26.
Feed-water Temperature when Condens-
ing ; L,oss in, 14.
Flooding due to Induction Condenser ; Pre-
vention of, 50.
Head and Pressure of Water; Relation
between, 2.
Heat. Effect of— upon a vacuum, 7.
Heat in a Pound of Steam, 54.
Heat Units required to convert Water into
Steam, 52-54.
I nduction Condenser , The, 47-51.
Induction Condenser , Adjustment of, 49.
Induction Condenser; Arrangement of, 48.
Induction Condenser ; Prevention of flood-
ing due to, 50
INDEX.
79
Induction Condenser; Stopping and start-
ing an engine equipped with an, 51.
Injection Main ; Size of, 67.
Injection ; Starting a balky, 34.
Injection Water Supply, 44,
Injector Condenser ; The, 24, 25 and 41-46.
Injector Condenser ; Advantages of, 45.
Injector Condenser ; Arrangement of, 43.
Injector Condenser ; Diagram of 42.
V et Condenser ; The, 28-35.
Jet Condenser ; Arrangement of, 29.
Jet Condenser; Starting and stopping an
engine equipped with an indepen-
dent, 35.
Jet Condensers ; Types of, 30.
K
n o w 1 e s Horizontal Double- Acting
Pumps ; Table of, 71.
Lift of Water by Vacuum, 6-7.
Ivaidlaw-Dunn-Gordon Horizontal Double-
Acting Pumps ; Table of, 72.
M
I easurement of Atmospheric Pressure, 3.
Measurement of a Vacuum, 4-5.
Motor-Driven Pumps, 40.
I^ressure ; Absolute, 9.
Pressure and Temperature ; Relations be-
tween, 8-9.
Pressure of a Column of Water, 2.
Pressure of the Atmosphere, 3.
Pump ; Air. See Air-pump.
Pump Displacement required for Water to
Condense, 57.
Pump ; Circulating, 39-40.
Pump Rating, 61.
Pump Suction, 6-7.
Pump Tables ; See tables of pump data.
Pumps ; Motor-driven, 40.
Pumping Air, 10.
Pumping Hot Water, 7-8.
f"l elief Valves, 31.
Starting and stopping an engine equipped
with Induction Condenser, 51.
Starting an engine equipped with a Jet Con-
denser, 33.
Steam below Atmospheric Pressure ; Tem-
perature of, 8.
Steam ; Heat, in a pound of, 52.
Steam ; Heat required to convert water
into, 52-54.
Steam ; Physical properties of, 53.
Steam ; Water required to condense, 15, 16
and 55-57.
Stopping an engine equipped with a Jet
Condenser, 35.
Surface Condenser ; The, 23 and 36-40.
Surface Condenser ; Air-pump for, 65.
Surface Condenser ; Area of cooling surface
in, 65-66.
Surface Condenser ; Details of the, 37-38.
Surface Condenser ; Sectional view of a, 37.
Snow Horizontal Double-Acting Pumps ;
Table of, 73.
I ables of Pump Data :
Barr Horiz. Double-Acting, 77.
Conover Vert. Single-Acting, 69.
Dean Bros., Horiz. Double-Acting, 70.
Dean Bros. Twin Cylinder Vertical
Single-Acting, 76.
Deane Horiz. Double-Acting, 75.
Knowles Horiz. Double-Acting, 7:.
I,aidlaw-Dunn-Gordon Horizontal
Double-Acting, 72.
Snow Horiz. Double-Acting, 73.
Worthington Horiz. Double-Acting,
74-
Temperature and Pressure ; Relation be-
tween, 8-9.
Temperature and Vacuum ; Relation be-
tween, 68.
Temperature of Feed- Water when Condens-
ing, 14.
Temperature of Steam below Atmospheric
Pressure, 8.
Tower ; Cooling, 26.
Vacuum and Temperature ; Relation be-
tween, 68.
Vacuum Breakers. 31-32.
Vacuum ; Effect of heat upon a, 7.
Vacuum ; lifting water by means of a, 6-7.
Vacuum ; Measurement of a, 4-5.
Vacuum produced by Condensation, ir.
Valves ; lifting or clattering of air-pump,
27.
Valves ; Relief, 31.
W ater Column ; Pressure of a, 2.
Water to Condense ; Pump displacement
required for, 57.
Water ; Feed. See Feed water.
Water lifted by means of a Vacuum, 6-7.
Water ; Pumping hot, 8.
Water required per Horsepower for Con-
densing, in gallons, 67.
Water required to Condense Steam, 15-16
and 55-57.
Water into Steam ; Heat units required to
convert, 52-54.
Water Supply ; Injection, 44.
Worthington Horizontal Double-Acting
Pumps ; Table of, 74.
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361847
Low, F.R. L9
Condensers.
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