Ernest Victor Lallier.

An elementary manual of the steam engine; containing also a chapter on the theory, construction and operation of internal combustion engines for the operating engineer online

. (page 10 of 17)
Online LibraryErnest Victor LallierAn elementary manual of the steam engine; containing also a chapter on the theory, construction and operation of internal combustion engines for the operating engineer → online text (page 10 of 17)
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6. Name some advantages due to its use?

7. Why do the cylinders di£fer in size?

8. How are the total number of expansions determined?

9. What is a condenser?

10. Describe a surface condenser; a jet condenser.



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CHAPTER XVn.
PIPES AND FITTINGS.

In order to connect the boilers, engines, pumps, and
various other pieces of apparatus so that steam and water
may flow between them, hollow iron conductors called
][dpe8 are employed.

The pipes are joined by the use of small properly
shaped pieces, suitably threaded, called '* fittings."

Pipes are either welded or riveted, according to their
size. Steam piping is spoken of in terms of the inside
diameter or size of the opening. For example : A half-
inch pipe implies that the inner diameter is approximately
one half inch. The outer diameter would probably be
nearly three quarters of an inch. Similarly, a one-inch
pipe would have an exterior diameter larger than one
inch, while the opening would be approximately one inch
in diameter.

Tubing, however, under which head would be placed
brass pipe and boiler tubes, is measured by its outside
diameter.

Pipe is supplied in lengths having a thread at each
end. Pipe threads, as well as the threads in all fittings,
where such are required, unless otherwise specified,
are supplied as right-hand threads. This means that
in turning a right-hand screw or thread, in order to
tighten it, it will be turned in the same direction as that
taken by the hands of a clock; and in the reverse direc-

174



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PIPES AND FITTINGS, 175

tion in order to loosen it. Conditions sometimes require
the use of a thread working in the opposite direction.
When this is the case a left-hand thread must be
specified.

When connecting two pieces of pipe, one being a con-
tinuation of the other, a short piece of pipe, threaded
internally to fit the external threads on the pipe ends, is
used. This fitting, as shown in section. No. i, Fig. 71,
is called a coupling. The threads on the ends of steam
pipes are made tapering ; that is, the front end is smaller
in diameter than the rear end. Threads in fittings are
tapered in a similar manner. This makes it easier to
screw together at the start and the further they are
turned the tighter the threads get, finally wedging to-
gether as a steam-tight joint, which would, of course, be
impossible were the threads parallel in diameter as is
the case in an ordinary machine screw.

It is sometimes required that the ends of two pipes
already in position be connected as in the previous case,
so that screwing the coupling up on one pipe would
unscrew it from the other, in case all right-hand threads
are used. In such a case, the external thread on one
pipe end is made left-handed and the other right-handed
and a similarly threaded right and left coupling is
employed. On account of the difference of angle in
the threads both will tighten up or loosen at the same
time. The external appearance of this coupling differs
from the previous one in having several straight, raised
projections, lengthwise of itself.

When necessary to join two pipes at right angles with
each other a fitting called an elbow or ell is used. No. 2,



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176 ELEBftENTART STEAM ENGINEERING.
















Kg. 71.



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PIPES AND FITTINGS. 177

Fig. 71. Unless otherwise specified, these elbows are
supplied with openings at 90"" to each other. They may,
however, be obtained with openings at other angles to
each other as well as with an additional opening on the
side of the elbow, if so desired.

Where a line of pipe is joined in some part of its
length by another pipe at right angles to it, the joint is
formed by a fitting called a Ue, No. 3.

Where two lines of pipe cross each other, forming four
right angles, a fitting called a cros» is employed, No. 4.

If it is desired to join two pipes of different diameters
with one fitting it is done by the use of a fitting having
openings of the required diameters for the two sizes
of pipe and this is called a reducing coupling^ or elbow,
as the case may be.

If it is desired to screw a pipe into a larger fitting
the space between the two may be filled by the use
of a bushing as shown in No. 5. This is a piece of
material having an internal thread to fit the smaller
and an external thread to fit the larger size with a
hexagonal shape at a, to fit a wrench, for convenience
in tightening.

If two fittings or valves are placed close together and
only a short piece of pipe is required to join the two, this
pipe is called a nipple, No. 6. If this is so short
that the threads meet, as shown in No. 6j it is called a
close nipple. If there is, perhaps, half an inch of blank
space between the threads, it is called a short nipple,
and one somewhat longer, extending to two or three
inches in total length, would be called a long nipple.

If it is desired to close the end of a pipe^ the cap.



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178 ELEMENTARY STEAM ENGINEERING.

No. 7, is used; or to close the opening in a fitting, tlie
plug, No. 8, will serve.

Sometimes the right and left coupling may not be
convenient to join pipes, under the conditions previously
mentioned. For this purpose we will employ a fitting
called a union, No. 9. It consists of three pieces,
two of which, a and a', are threaded internally with
right-hand threads. These screw on the ends of the
pipes to be joined together. The loose collar h slides
over the portion a of the union and is stopped by the
projecting rim. It is then screwed on to a'; the tighter
it is screwed in position the closer the two portions of
the union, a and a', are drawn together.

In the case of the common union, opposing surfaces of
a and a' are separated by a washer, made of packing, in
order to enable a tight joint to be formed. In the better
grade of unions this is a grotmd joint, the face in contact
being turned to a hemispherical form and then carefully
ground to a tight fit. No washer is required in this case.

In joining the ends of large pipes together, or to
valves, the flanged coupling. No. 10, is largely used. It
consists of a disc threaded internally to receive the pipe
and having on the flat portion several holes to receive
the bolts. These are used in drawing the faces of the
flange firmly together. The space between the faces
is filled either with sheet packing, copper or other suit-
able material. Occasionally the inner edge of the
thread is chamfered off, and the pipe having been
screwed home is peened over, after which the entire
flange and pipe is machined absolutely true in order
to make a first-class joint.



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PIPES AND FITTINGS. 179

In steam heating the radiators are sometimes made
of a number of pipes, parallel with each other and screw-
ing into one casting at the end. Such a fitting is called
a header f No. 11. Again the radiator will sometimes
consist of pipes parallel to each other, connected from
one to the other in zig-zag fashion, the fitting in this
case being called return bends, No. 12. These fittings
and valves are not, by any means, all of those employed
in steam-fitting work, but they comprise the principal
ones in ordinary use. Other fittings employed will be
needed only in special cases and to meet extra condi-
tions, and even then they will vary in shape, but not in
principle, from those illustrated.

VALVES.

In order to control the flow of a liquid through pipes,
valves are employed. These are really nothing more
nor less than suitably constructed fittings of various
kinds so arranged that they may be operated either
automatically or by hand.

In Fig. 72, showing a globe valve which is repre-
sentative of a large number of valves used in an engine
plant, the main casting, spherical in shape, gives it its
name, the globe valve.

At a is a circular plate or disc, the lower surface being
either flat or beveled and of metal or other suitable
material, and forming the actual door which is opened
or closed, o is a ring which forms the seat of the valve.
The surfaces of a and o, which come in contact, are
accurately fitted in order that they may be steam-tight
when closed. The rod, &, is the stem of the valve.



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l8o ELEBftENTART STEAM ENGmEERING.



Fig. 72.

The lower end is so fitted into the projection on the
upper part of the disc that it is free to revolve in the disc
and yet cany the disc with it. On the stem is shown a
thread which screws into the nut, d. This enables the



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PIPES AND FITHNGS. l8l

valve to be opened or closed by turning the stem by
means of the hand-wheel, e. In order to prevent
leakage through the threaded portion of the stem, the
stufBng box is provided, as shown. This consists of a
recess made in the projecting hub which is filled with
asbestos wicking. The gland, ^, is pressed down upon
the asbestos by means of the nut, h. This forces the
packing snugly around the valve stem and prevents any
leaks. The ends of the body are shown threaded to
fit the steam pipe.

In its passage through this valve, as indicated by the
arrows, the steam must make two right-angle bends
which, of course, produce considerable friction.

These valves are sometimes made with the threaded
portion of the pipe at right angles to each other. They
are then called angle valves, but the same principle of
construction holds good in all cases.

In the larger forms, with slightly different details of
construction, they are used as the main valves on engines
and boilers, in which case they are called stop valves.

In the large sizes, instead of being threaded to receive
a pipe, they are supplied with flanges, by means of which
they may be bolted into position.

Mention has been made of the fact that the course of
the steam through this valve is rather indirect. This
would become a serious objection were the heavier
fluids, such as water, employed. To overcome this
difficulty, valves on water lines are often of the straight
way or gate valve type. Such a valve has the seat and
disc, as before, with the exception that they are placed
in a vertical position.



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i82 ELEMENTARY STEAM ENGINEERING.

The disc proper is somewhat wedge shaped. The
seat is composed of two parts, a and &, Fig. 73, the front
portion a being the seat proper, as before, and when the



Fig. 73.

valve closes, the rear portion &, an inclined surface on
which the disc slides, forces the valve disc tightly
against the seat a as the disc is lowered by means of the
valve stem connected in similar manner to that of the
globe valve. This construction is shown in Fig. 73,



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PIPES AND FITTINGS, 183

which also makes it clear that the passage of the liquids
through this valve will be in a continuous straight
line.

Another valve largely used for certain purposes in the
engine and boiler room is of the plug type, as shown
in Fig. 74. This is similar in construction to the valve



Fig. 74.

used on the ordinary gas jet, consisting of a body in
which is made a tapered hole.

A tapered plug is fitted into the hole, both being
carefully ground together. The nut and screw on the



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l84 ELEMENTARY STEAM ENGINEERING.

plug enable us to draw the plug farther in the hole and
tighten the valve, in case of a tendency to leak.

A combination to some extent of the plug and globe
valves, carefully packed under heavy pressure, is used
for boiler blow-off valves. These are made unusually
strong because, due to the position in which they are
placed, they cannot so readily be observed. Their work
is extremely important for, should a serious leak occur,
they will possibly allow the water to flow out of the boiler
when in operation, thus producing serious results.



Fig. 75.

Another very important and largely used valve around
the steam plant is known as the check valve. This is
an automatic valve, in the sense that it will take care
of its own operation. It is designed to allow the flow of
liquids or gas only in one direction.

Figs. 75, 76, and 77 illustrate three types of check
valves. In Fig. 75 is illustrated a swinging check valve.
The body is similar in construction to that previously
shown, except that there is no stem present and the



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PIPES AND FITTINGS. 185

valve disc rests upon a seat placed at an angle in the
valve body. The disc swings by means of the arm b
from the pivot. Liquid, passing in the direction of the



Fig. 76.

arrow, will lift the disc, and pass on. Any attempt to
flow in the opposite direction will close the valve, and



Fig. 77.

the greater the pressure, the more tightly the valve
will be closed. The cap, shown at a, is necessary for
placing in position the disc and the arm.



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i86 ELEMENTARY STEilM ENGINEERING.

In Fig. 76 is shown a ball check valve. The ball seen
resting on its seat is lifted by the pressure below it into
the recess above, allowing the flow of liquid in one
direction. The pressure produced in the other direc-
tion forces the ball down to its seat, thus closing the
valve.

In Fig. 77 a similar valve is shown, the only difference
being that, instead of a ball, the disc is used as before.
This is guided in the recess by the wings or vanes,
shown above it. The method of operation is similar
to that previously described.

Sometimes steam is desired at a lower pressure than
that in the boiler. Suppose, for example, the boiler is
supplying steam at 80 pounds to run the engine, and
steam at 8 or 10 pounds is desired for some heating
apparatus. This must be taken from the boiler supply-
ing steam at the higher pressure. This reduction is
accomplished by throttling the steam with a reducing
valve. These may be operated automatically and a
constant pressure maintained in the steam pipe. In
one instance. Fig. 78, a diaphragm of rubber material
is placed at a, having its edges clamped by means of
the bolts &, extending around its circumference. The
center portion of the diaphragm is held by means of the
nuts above and below, shown on the spindle or stem of
the valve v. The steam pressure acts on the lower side
of the diaphragm tending to lift and close the valve,
while the weight set to produce the desired pressure
tends to open it. The movement of the diaphragm,
due to either of these causes, produces a shifting of
the balanced valve v. When live steam is turned on, the



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PIPES AND FITXraOS.



187



valve is full open. This is due to the pressure of the
weight above. When the pressure passing through
and acting on the diaphragm equals the weight above,




Fig. 78.

the tendency of the valve is to close. Therefore, this
action maintains the valve open just sufficient to allow
enough pressure per square inch to be maintained on
the side e of the valve.

In all plants there is more or less loss, due to con-
densation. Particularly is this the case where long



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i88



ELEMENTARY STEAM ENGINEERING.



lines of steam supply or steam-heating pipes are used.
It is necessary to get rid of this entrained water of con-
densation as soon as possible, both in order to prevent
annoyance and injury and also to prevent greater con-
densation taking place, due to the presence of the cooler
water.
For this purpose steam traps are employed. The




Fig. 79.



principle of construction is extremely simple. The ob-
ject to be obtained is to rid the pipes of the condensed
water without allowing the steam to escape. Such a
trap, Fig. 79, consists essentially of a chamber con-
nected to the steam pipes at such a point that any con-
densed water will readily flow into the main body' of
the trap and there be collected. Forming a portion of the
trap is the valve v^ which is normally closed, due to the



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PIPES AND FITTINGS, 189

weight of the lever ;, and the float /, pressing down
upon it. The float may be a hollow metallic ball or
receptacle of any suitable size or shape. As the water
collects in the main body of the trap and finally reaches
a height sufficient to lift the float, this action will open
the valve, allowing water to flow out, nearly emptying
the trap. As the steam is pressing on the upper sur-
face of the water, and the lowering of the level of the
water causes the float to drop and the valve to close
before all of the water has passed out, there consequently
is no chance for the steam to escape at any time, because
it is trapped by the presence of the remaining body of
water between itself and the opening, and the trap is
never entirely drained while in use.

In the main steam pipe from the boiler to the engine
it is also advisable to place a steam separator, because,
even in a properly designed and installed steam plant,
more or less moisture is carried over with the steam
into the engine cylinder, and conditions may arise
which will cause an increase in the amount of this
moisture. Some means, therefore, should be taken to
separate it from the steam in its passage to the engine.
The principle of such a steam separator is shown in ,
Fig. 80 where the steam, instead of being allowed to
pass directly along the pipe, makes several changes in
direction by striking the baffle plates &, placed in the
main chamber of the separator. The steam at high
speed readily changes its direction. The weight of the
entrained water, however, and its momentum causes
it to be carried in a straight line and strike the sides of
the metallic plates to which it will cling in preference



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IQO



ELEMENTARY STEAM ENGINEERING.



to passing on with the steam. The water then runs
down the plates and collects in the receiver at the bot-
tom, whence it is drained by the steam trap.

Of somewhat similar design to the steam separator
is the grease extractor or separator, employed where the



I I



;;



w%



%



^i 0* W>



^ n ^

J



^ I



y ? f,



mm^




fig. 80.

condensed water from the exhaust steam is to be used
over again. It is necessary to cleanse this water of the
cylinder oil and other grease, which it may have col-
lected on its passage through the engine, and to do this
it is allowed to pass into a large vessel, a portion of



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PIPES AND FITTINGS. 191

which is occupied by either gratings or chains or similar
objects suspended in the path to be taken by the exliaust
steam. The contained oil and grease, to a very large
extent, collects on the surface of these metallic bodies.
The steam, in the form of condensed water, then passes
to a supplementary purifjring chamber and then being
practically free from all grease and oils, collects in a
reservoir from which it may be ptunped for use.

EQUATION OF PIPES.

It is frequently desirable to know what ntunber of
one-sized pipes will be equal in capacity to a single given
pipe for delivery of steam, air, or water. At the same
velocity of flow, two pipes deliver as the square of their
internal diameters; but the same head will not produce
the same velocity in pipes of different sizes or lengths,
the difference being usually stated to vary as the square
root of the fifth power of the diameters. The friction
of a fluid within itself is very slight, and therefore the
main resistance to flow is the friction upon the sides of
the conduit. This extends to a limited distance, and is
greater in proportion to the contents of a small pipe,
than of a large one. In a given pipe it is equal, approxi-
mately, to a constant, multiplied by the diameter, or
the ratio of flow found by dividing some power of the
diameter, by the diameter increased by a constant.
Careful comparison of a large ntmiber of experiments by
different investigators has developed the following as
a close approximation to the relative flow in pipes of
different sizes under similar conditions:

Woe ^ 01 y 9

€1 + 3.6 Vcl + 3.6



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192 ELEMENTARY STEAM ENGINEERING.

W being the weight of fluid delivered in a given time,
and d being the internal diameter in inches.

FLOW OF STEAM THROUGH PIPES.

The approximate weight of any fluid which will flow
in one minute through any given pipe with a given head
or pressure may be found by the following formula:



jfT^sr f^MEM^



L



(■+¥) '



in which W — weight in pounds avoirdupois, d = diam-
eter in inches, JD = density or weight per cubic foot,
Px — the initial pressure, pf^ = pressure at end of pipe
and L — the length in feet.

The table on page 193 gives, approximately, the weight
of steam per minute which will flow from various initial
pressures, with one pound loss of pressure, through
straight smooth pipes, each having a length of 240 times
its own diameter.

For sizes of pipe below 6 inches, the flow is calculated
from the actual areas of '^ standard" pipe of nominal
diameters.

For horse power multiply the figures in the table by 2.
For any other loss of pressure multiply by the square
root of the given loss. For any other length of pipe
divide 240 by the given length expressed in diameters,
and multiply the figures in the table by the square root
of this quotient, which will give the flow for i pound loss
of pressure. Conversely, dividing the given length by
240 will give the loss of pressure for the flow given in
the table.



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PIPES AI7D FimNGS.
FLOW OF STEAM THROUGH PIPES.



193





Diameter in inches. Length 240 diameters.


Initial gage


i


I


li


2


2i


3


4


5


6


pressure.




















Pounds per




square inch.


Weight of steam per minute, z pound pressure loss.


I


I.16


2.07


5.7


10.27


1545


25.38


46.85


95^8


115.9


10


1.44


2.57


i\


12.72


19.15


31.45


58.05


X


20


1.70


3.02


14.94


22.49


3^.94


68.20


1 12.6


30


I.91


3.40


94


16.84


25.35


41.63


tf


126.9


190.X


40


2.10


3.74


10.3


18.51


27.87


45.77


139.5


209.


§^


2.27


4.04


11.2


20.01


30.13


49.48


91.34


150.8


226.


60


2.43


4.32


11.9


21.38


32.2


52.9


97.6


161.1


241.5
255.8


IS


2.57


4.5«


12.6


22.7


34.1


56.


103.4
108.7


170.7


^'7}


4.82


13.3


23.8


35.87


58.9


179.5


269.


90


2.83


5.04


13.9


24.9


37.5


61.6


"3.7
1 18.5


187.8


281.4


100


2.95


5.25


14.5


26.


39.1


64.2


195.6


203.1



The loss of head» due to getting up the velocity, to the
friction of the steam entering the pipe, and passing
elbows and valves will reduce the flow given in the
tables. The resistances at the opening and at a globe
valve are each about the same as that for a length
of pipe equal to 114 diameters divided by a number
represented by i + (3.6 -^ diameter). For the sizes
of pipes given in the table, these corresponding lengths
are:



Diameter in inches


i


I


li


2


2i


3


4


5


6


Equivalent pipe,
length in feet


20


25


34


41


47


52


60


66


71



The resistance at an elbow is equal to two-thirds of
that of a globe valve. These equivalents — for open-



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194 ELEMENTARY STEilM ENGINEERING.

ings, for elbows, and for valves — must be added in
each instance to the actual length of pipe. Thus a
4-inch pipe, 120 diameters (40 feet) long, with a globe
valve and three elbows, would be equivalent to 120 +
60 + 60 + (3 X 40) = 360 diameters ; and 360 ^ 240 = 15.
It would, therefore, have 13 pounds loss of pressure at
the flow given in the table, or deliver (ij^ VTj = 0.816)
81.6 per cent of the steam with the same (i pound) loss
of pressure.

FLOW OF STEAM FROM A GIVEN ORIFICE.

Steam of any pressure flowing through an opening
into any other pressure, less than three-fifths of the
initial pressure, has practically a constant velocity,
888 feet per second, or a little over ten miles per minute;
hence the amount discharged in pounds is proportionate
to the weight or density of the steam. To ascertain
the pounds, avoirdupois, discharged per minute, mul-
tiply the area of opening in inches by 370 times the
weight per cubic foot of the steam.

Or the quantity discharged per minute may be ap-
proximately found by Rankine's formula:
IT = 6 op -^ 7,

in which w = weight in pounds, a = area in square
inches, and p = absolute pressure. The theoretical
flow requires to be multiplied by a constant k = 0.93
for a short pipe, or 0.63 for a thin opening, as in a plate,


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Online LibraryErnest Victor LallierAn elementary manual of the steam engine; containing also a chapter on the theory, construction and operation of internal combustion engines for the operating engineer → online text (page 10 of 17)