_It happens at times_ that a pump, with the full pressure against which
it is expected to work, resting upon the discharge valves, refuses
to lift water for the reason that air within the pump chamber is not
dislodged, but only compressed by the motion of the plunger. It is
well, therefore, to arrange for running without pressure until the air
is expelled and water follows. This is done by _placing a check valve
in the delivery pipe, and providing a waste cock in the discharge
chamber to be closed after the pump has caught water_. A stop valve is
also required for shutting off the back pressure when the pump can be
opened for examination of the valves.
* * *
If any difficulty is experienced in making a pump work properly when
first started, it will generally be found in leaks through _imperfect
connections_, or from the temporary stiffness to be expected in a new
machine, or perhaps leaky valves.
* * *
If, when standing at the suction end of a centrifugal pump, looking
over pump shell toward pulley, the top of shaft revolves from right to
left, or against the sun, _the pump is right hand_, and if from left to
right, or with the sun, _it is left hand_.
* * *
_A pump should be located in a convenient_ as well as a clean place.
It should be well set upon a suitable foundation, so that it may be
free from vibration or jar; this “note” applies to direct-acting,
self-contained pumps, as well as to others.
* * *
The economical operation of a pump depends, to a great extent, upon the
kind and condition of the packing in the stuffing-boxes and pistons,
its quality, adaptability to particular requirements, and the method of
placing it in the stuffing-boxes and plungers.
* * *
Almost all the stuffing-boxes on pumps are too shallow and the glands
too short. To keep a rod tight under these conditions the packing must
be of the proper size and quality, and it must be put in with a view to
securing the greatest possible degree of elasticity, so that the rod
may be kept tight with the least pressure on the packing.
* * *
To do this, it is best to select packing which will permit a number of
narrow rings to be used instead of a few wide rings. The rings next to
the bottom will become dry and hard before those next to the glands of
the box are half worn out. If a number of narrow rings are used, the
dry ones may be removed and duplicated by new ones and replacing the
rest of the packing in the stuffing-box. This method economizes packing
and secures a tight yet freely working rod.
* * *
When patent square packings are used, it makes less difference whether
the rings are narrow or wide, because the surface in contact with the
rod will be nearly continuous in either case.
* * *
When cutting packing rings, the length should be such that the ends do
not come together within 1/8 inch when put into the stuffing-box, and
the rings are put in to break joints, which prevents leakage through
them.
When inserting this packing, the rings are put in one at a time, using
a piece of hard wood to push them to the bottom of the stuffing-box and
firmly against one another. The stuffing-box should be filled as full
as it can be, and start the nuts on the studs by hand. Screw up the
nuts with the hand and then start the pump slowly. If leakage occurs
do not attempt to tighten the nut while the rod is in motion, and in
all cases tighten it only enough to stop the leakage. A slight leakage
at the water end is not harmful. A little cylinder oil and graphite
occasionally applied to the rod will tend to keep it smooth and bright,
which condition is favorable to the durability of the rod and of the
packing.
* * *
When cutting rings of packing for the water piston or plunger, the
rings should be 1/8 inch short, as previously described, page 372.
* * *
Packing should fit the grooves in solid pistons moderately tight, so
that the packing can be pushed into the grooves with the fingers.
The depth of the packing should be such that the piston will fit the
bore of the water cylinder snugly when first put in. If packing of
the proper depth cannot be obtained, it is better to have the grooves
turned to receive standard sizes of packing and not require special
sizes. Cutting hydraulic packing is a tedious job, consuming a great
deal of unnecessary time.
* * *
_It takes less power to feed into the bottom of a tank than it does
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 delivery 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 additional length of pipe outside.
* * *
_The duty of the air pump is solely to get rid of the water and air in
the condenser._ It adds to the efficiency of the condensing apparatus,
and renders its operation continuous; its valve being thrown by the
action of its own piston, it must complete its stroke in length whether
the piston is moving in air, water or vapor.
_Pumps should be kept clean internally and externally._ In order to
keep a pump clean internally it must be inspected and oiled internally
at regular intervals the same as it is externally.
* * *
When pumps fail to work properly the difficulty is generally located in
one of three places, viz.: _the water end, the steam end or the suction
pipe_.
* * *
The several parts of the valve gear of a single cylinder pump _should
be marked when the pump works properly_, then any trouble due to the
slipping of the collars or tappets can readily be remedied; if the
nuts and set screws are kept tight, derangements occur only at long
intervals.
* * *
The principal difficulties encountered with steam pumps are not
generally due to improper steam distribution, but to wear, as may be
seen; hence by inspecting pumps at regular intervals many unpleasant
occurrences and accidents can be avoided.
* * *
_The steam pipe leading to a pump_ should be so arranged that the
water of condensation, while the pump is idle, may not pass through
the steam chest and cylinders, and wash off the lubricating oil. Drip
cocks should be attached to steam pipes and all large pipes should have
separators and steam traps.
* * *
Pumps that are generally operated at moderately high speeds and with
high lifts may be made to work more smoothly by placing a _vacuum
chamber on the suction pipe_.
* * *
_Valves in the suction pipe_ should have the stems carefully packed
and kept tight; air leaks in valve stem stuffing-boxes are too often
overlooked.
* * *
_Stoppage of the suction pipes_ or chamber is generally indicated by a
jerky action and pounding of the plungers or water pistons, while a
dull thud at the ends of the stroke is more often due to a lack of air
in the air chamber, or when the speed is high, to a lack of capacity in
the air chamber.
* * *
_The steam ends of pumps_ require the same lubrication as the cylinders
and valves of engines. Intermittent lubrication is never to be
recommended even for slow running pumps. Sight feed oil cups are always
preferred.
* * *
_A sight feed lubricator_ connected to the steam pipe below the
throttle or to the steam chest is _automatic in its operation_. All
that is necessary is to fill it. When the speed increases the feed
increases and when the pump stops the feed stops. An oil hand pump is
also desirable to introduce a mixture of oil and graphite, about 10 per
cent. of graphite.
* * *
_The water end stuffing-boxes of a pump_ may be lubricated by putting
a heavy grease on the piston rods, or good cylinder oil may be used
when grease is not at hand. _Some of the grease works into the
stuffing-boxes_ and furnishes better lubrication than can be obtained
by the water alone. Care must be used not to use too much oil as it
must not go beyond the stuffing-boxes and contaminate the water.
* * *
When a pump works properly under high pressures and fails to work under
low pressures, the difficulty is generally found _in the lift of the
valves_.
* * *
_When the water end of a pump_ is known to be in good condition failure
to run properly will in all probability be discovered _in the steam
end_, and in single cylinder pumps the fault is generally caused
by clogging of the auxiliary valves and ports. Sometimes pieces of
packing break off and get into these small ports, thus shutting off the
admission or release of steam.
* * *
_When one side of a duplex pump_ makes a quick stroke it indicates
either that the stuffing-box gland of the opposite side is too tight
or that the packing in the cylinder of the side making the quick
stroke is wearing out or has, perhaps, given way. A broken discharge or
suction valve will also cause a “jerky“ motion of the pistons.
* * *
Pumps should be examined frequently in order _to know what parts are
beginning to wear_ and how fast the wear is taking place. When this
is done the worn parts can, in the majority of cases, be taken out
and replaced by new ones before they give out entirely, thus avoiding
delay, but what is better, _duplicated parts kept on hand_ ready at a
moment’s notice.
* * *
The regular inspection _of the screen in the separating chamber_ in the
suction pipe renders frequent inspections of the interior of the pump
unnecessary, the inspection previously alluded to is generally easier
and more quickly done.
* * *
_Considerable wear can and frequently does take place in a pump_ in the
course of six months, and for this reason it is advisable to inspect
the interiors at shorter intervals, say four months for general service
pumps and once in three months for boiler feed pumps. More frequent
inspections should be made when handling dirty water.
* * *
_When a pump has to run faster one week than the week previous_ in
order to supply approximately an equal volume of water, the plungers
and valves should be examined, because such behavior indicates leakage.
* * *
_The sight feed lubricator should be filled in the morning_ so as to
be empty by night, thus permitting the water to be drained out without
wasting oil. Draining the delivery valve chest will also drain the
delivery pipe up to the check valve if those pipes are above the chest
and without water seals in them. If this pipe is arranged below the
pump, then separate drain cocks should be provided and should be placed
at the lowest positions in the piping.
* * *
_When a pump fails to start after standing for some time_ it should be
primed by filling the barrel with water and starting the pump slowly.
If after priming it fails to raise water, the suction pipe should be
examined and also the plungers and the valves. If the plunger packing
has become dry and hard, merely filling the water end with water will
not at once remedy the trouble because the packing must be thoroughly
soaked before it will work properly.
* * *
_Pumps should be packed with the same care and consideration as is used
with the best steam engines._ The rods should be packed just tight
enough to prevent leakage, and the packing renewed often enough to keep
it soft and pliable, in which state it readily absorbs oil. Old packing
will upon examination be frequently found full of sand and small
particles of grit.
* * *
_Metallic packings_ are now extensively used on steam piston rods and
upon the rods of air pumps.
* * *
_When priming and draining a pump_ the air cock in the air chamber
should also be opened. The drain and cylinder cocks at the steam end
should be opened before closing the throttle; the steam should be shut
off at the boiler when stopping at night so as to drain the entire pipe.
* * *
_Pumps that are exposed to low temperatures in winter_ should be
provided with removable drain plugs or drain cocks for emptying the
cylinders and valve chambers of water and also allowing the water to
flow out of the suction pipe.
* * *
_The friction in pipes_, whether of cast iron, steel or copper, depends
upon the internal smoothness of the pipe and the velocity of the
water, as well as the number and kind of ells, tees and valves in the
pipe. Wrought iron lap welded pipe, for steam, is preferable to either
cast iron or copper. It is smoother internally than cast iron, and is
lighter and costs less than copper, and is much stronger and safer than
either.
* * *
It may be said 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
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 a decided gain in almost all cases.
* * *
_One pound of steam at atmospheric pressure_ occupies 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 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 vertical 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 but little above atmospheric pressure.
* * *
_The velocity of water entering a suction pipe_ depends upon two
things, the vacuum in the pipe and the vertical lift of the water.
The longer the suction pipe, vertically, the greater the frictional
resistance to the flow of water; the flow of water through small
discharge pipes should not exceed four hundred feet per minute, and for
large pipes five hundred feet per minute.
* * *
_A locomotive-boiler compound._ The lines of a certain great R. R.
traverse a country where the water is very hard and they are compelled
to resort to some method of precipitating the lime that is held in
solution. After many tests and experiments they have made a compound
and use it as follows: in a barrel of water of a capacity of fifty
gallons they put 21 lbs. of carbonate of soda, or best white soda ash
of commerce, and 35 lbs. of white caustic soda; the cost, per gallon,
is about 2-1/2 cents. The compound is carried in this concentrated
form, in calomine cans on the tender of each locomotive. A certain
amount, according to the necessities of the case, is poured into the
tender at the water tank at each filling. This amount is determined
by analysis, and varies all the way from two to fifteen pints for two
thousand gallons of water. The precipitating power of this compound
may be taken roughly at 2/3 of a pound of the carbonate of lime, or
equivalent amount of other material, per pint of the compound. On their
western lines where they are dealing with alkali waters and those
containing sulphates, the company use merely 60 pounds of soda ash to
a barrel of water. When the water is pumped into the boiler the heat
completes the precipitation and aggregation of the particles, and this
does away with all trouble of the boiler or injector tubes clogging up.
* * *
It has been recently determined by some German experimenters that
_sugar effects a strong action in steam boilers_; it has an acid
reaction upon the iron which dissolves it with a disengagement of
hydrogen. The amount of damage done increases with the amount of sugar
in the water. These results are worthy of note in sugar refineries and
places where sugar sometimes finds its way into the boilers by means
of the water supplied. The experiments in question also show that zinc
is strongly attacked by sugar; copper, tin, lead and aluminium are not
attacked.
* * *
_White oak bark, used by tanners_, has an excellent effect on boiler
incrustations. It may be used as follows: Throw into the tank or
reservoir from which the boilers are fed a quantity of bark in the
piece, in sufficient quantity to turn the water to a light brown
color. Repeat this operation every month at least, using only half
the quantity after the first month. Add a very small quantity of the
muriate of ammonia, about one pound for every 2,000 gallons of water
used. This will have the effect of softening as well as disintegrating
the carbonate of lime and other impurities deposited by the action of
evaporation.
NOTE.—Care must be exercised in keeping the bark, as it becomes
broken up, from the pump valves and blow-off valves. This may be
accomplished by throwing it into the reservoir confined in a sack.
_Among the best samples of boiler compounds_ ever sent to the
laboratory for analysis were those found to be composed of:
Sal-soda 40 Pounds
Catichu 5 „
Sal-ammoniac 5 „
This solution was formerly sold at a good round figure, but since its
nature became more generally known, it is not found in the market, but
it is largely used, consumers putting it up in lots sufficient to last
a year or so at a time.
The above is strongly recommended by those who have used it, one pound
of the mixture being added to each barrel of water used, but after the
scale is once thoroughly removed from the boiler, the use of sal-soda
is all that is necessary.
* * *
_There are other evils sometimes inherent in hard waters_ above the
mere production of a crust. Some waters contain a great deal of soluble
magnesia salts, together with common salt. When this is the case there
is a great probability of corrosion, for the former is attacked by
steam at high pressure in such a way that muriatic acid fumes are
produced, which seriously corrode the boiler, and what is far worse,
passes with the steam into the engine, and sets up corrosion in the
cylinders and other delicate fittings with which the steam comes in
contact. All this can, however, be obviated by the removal of the
magnesia from the water.
* * *
_When water attains a high temperature_, as it does under increasing
pressure, ranging from 175° to about 420° Fahr., all carbonates,
sulphates and chlorides are deposited in the following order:
First. Carbonate of lime at 176° and 248° Fahr.
Second. Sulphate of lime at 248° and 420°.
Third. Magnesia, or chlorides of magnesium, at 324° and 364°.
It is to take advantage of this fact that mechanically arranged jets,
sprinklers and long perforated pipes are introduced into the interior
of a steam boiler; these tend to scatter the depositing impurities
and also to bring the feed water more quickly to the highest possible
temperature.
_Where fuel is expensive_ and pumps are used for continuous service
under high and unusually high pressures it is oftentimes advisable to
operate the pumps condensing. This may be done, when the pump lifts
water by suction, without a separate condenser by connecting the
exhaust pipe with the suction pipe, as shown in Fig. 667. Assume that
the pump has been working properly for from 3 to 5 minutes with the
valve _A_ nearly closed and the valve _B_ a little open, the valve
_A_ is now quickly closed and _B_ opened. In operating these valves
both hands should be used, so that they may be opened and closed
simultaneously.
[Illustration: FIG. 667.]
_So penetrating is water at high pressure_ that only special qualities
of cast iron will be tight against it. In the early days of the
hydraulic jack it was no uncommon thing to see water issuing like
a fine needle through the metal, and the water needle is said to
penetrate the flesh as readily as one of steel.
The engraving, Fig. 668, represents a novel device for _preventing the
bursting of water pipes by freezing_. This is simply an air chamber
placed in the horizontal part of the pipe, with the chamber on top
side so that the ice may expand into this chamber, and so its force is
expended upon the air instead of bursting the pipe.
This device also acts as an air chamber and prevents “water hammer.” It
is made by the Anti-bursting pipe Co., Pittsburg, Pa.
_When it becomes necessary_ to make a quick connection into a main
steam pipe without breaking joints, a saddle such as either of those
shown in Fig. 669 and Fig. 670 may be applied by simply cutting or
drilling a hole through the main steam pipe.
[Illustration: FIG. 668.]
_To make the joint_, the rough lumps should be filed off the outside
of the pipe and red lead rubbed on to mark the surface, to show when
the fit is properly made. Then lay on with a brush a thin mixture of
red lead and varnish and quickly screw the saddle in place. Such joints
seldom or never leak when allowed to thoroughly dry before use.
[Illustration: FIG. 669.]
[Illustration: FIG. 670.]
When it becomes necessary to cut square packing to reduce its depth,
place the packing in a vise, allowing the stock to be removed to
project above the jaws, as shown in Fig. 671. With the aid of a
draw-knife the work can be quickly and easily done. It is difficult
to cut the packing evenly. If the rings have an uneven bearing on the
bottom of the grooves leakage is likely to occur when the pump is first
started.
_The follower type of water piston_ can readily be packed without
removing it from the cylinder, providing rings of the proper depth and
length are at hand. The old packing rings can be removed with a packing
hook. Take the new ring and start one end with a soft stick, and push
the remainder of the ring firmly against the collar or flange at the
inner end of the piston, as shown in the engraving, Fig. 672. Arrange
the several rings so as to break joints.
_Method of packing a follower piston._ Coat the sides of the rings with
a thick paste of cylinder oil and _Dixon’s Flake_ graphite, which will
prevent the rings from sticking together.
[Illustration: FIG. 671.]
_Pump packing cannot be readily examined_ and is liable to fail at any
time, therefore several rings, cut to the proper length, should be kept
on hand. This may be easily done by making a pattern ring, which is
nothing more or less than a ring of packing which has been fitted into
the piston and is known to be of the proper length. The extra rings can
then be cut at odd times, and when occasion demands it the water piston
can be packed very quickly and the pump started.
Care should be taken when about to pack a boiler feed pump or other
pump subjected to high pressure to see that the cylinders are relieved
before loosening the cylinder head bolts. This may be accomplished by
closing the valve in the delivery pipe, and also in the suction pipe;
if the pump receives water under pressure, open the air cock on the air
chamber and cylinder cocks.
[Illustration: FIG. 672.]
_Pump slip or slippage_ represents the difference between the
calculated and the actual discharge of a pump, which is generally
expressed as a percentage of the calculated discharge. Thus, when the
slippage is given as fifteen per cent. it indicates that the loss due
to slip amounts to fifteen per cent. of the calculated discharge.
Slippage is due to two causes, the time required for the suction and
discharge valve to seat, due to excessive speed. When the piston
speed is so high that the water cannot enter the pump fast enough to
completely fill the cylinder only a partial cylinder full of water is
delivered at each stroke. High speeds also increase slippage, due to
the seating of the valves.
_Graphite as a lubricant_ is almost without a rival. It is one of the
forms under which carbon appears in nature; it is also known under the
name of _plumbago_ and _black lead_; it is soft and oily to the touch;
it is a conductor of electricity; it is a lubricant that allows pipe
joints to be screwed up to the tightest possible fit. Graphite remains
upon the threads preventing rust, and it so preserves its peculiar
properties that pipe can be unscrewed without effort eight or ten years
after the joints have been made.
_It is difficult to lift hot water by suction, but not everyone can
explain the cause_; the reason is as follows:
[Illustration: FIGS. 673 AND 674.]
In Fig. 674, let A be a vessel in which a vacuum exists, and let it
communicate by a tube, as shown, to the lower vessel containing water.
The pressure of the atmosphere upon the surface will force the water
up into the pipe until the column is high enough to exert a pressure
per square inch equal to that of the atmosphere. A cubic inch of water
weighs about 1/28 of a pound, so that it will take 28 cubic inches to
weigh a pound, or a column 28 inches high to exert a pressure of one
pound per square inch. The atmospheric pressure is 14.7 pounds, or to
avoid fractions, say, 15 pounds. This pressure would then support a
column (15 × 28)/12 = 35 feet high; that is, the column _a-c_ in Fig.
674 would be 35 feet in height. Attach a gauge at or above the top,
_a_, of a column, and it will indicate a perfect vacuum; if the gauge
were attached 28 inches below _a_, it would indicate a pressure of one
pound above absolute zero, or a vacuum of 15-1 = 14 pounds; and if the
gauge were moved further downward, it would indicate an increasing
pressure, that is, a diminishing vacuum, at the rate of one pound for
every 28 inches of the water column above it, until at the level of the
water in the tank the pressure would be 15 pounds absolute, and the
vacuum would be zero.
Now, suppose the pipe to be lowered until the distance from the bottom
of the vessel, A, to the water level, _c_, is 21 feet. In that case we
will have the pressure of the atmosphere (15 pounds) forcing the water
up into the vessel, and the column 21 feet high, or (21 × 12)/28 = 9
pounds, opposing it. The difference, 15-9 = 6 pounds, is available to
force the water into the chamber. This arrangement is shown in Fig.
673, where A is a pump cylinder; then the difference in pressure, 6
pounds, lifts the valve, and the water enters the pump chamber with
a velocity due to that pressure. In order to insure smooth and quiet
running of the pump, it is necessary to keep the speed of the piston
inside of the velocity with which the cylinder would fill under this
pressure, reduced by the friction of the water, the pressure required
to lift the valves, etc.
But this supposes that there is a perfect vacuum in A, and we cannot
realize this in contact with hot water. Water at any temperature will
boil unless it is under a pressure equal to or greater than that
corresponding with the temperature. Water at 60 degrees F. will boil if
the pressure upon its surface is reduced to a quarter of a pound per
square inch, and in the case shown in Fig. 674, it would boil and fill
the space A with steam at that absolute pressure.
NOTE.—Water at 170 degrees F. will boil if its pressure is reduced
below 6 pounds absolute, and if the water were at this temperature
in Fig. 673, the cylinder, A, would be filled with steam at 6 pounds
pressure; and this added to the 9 pounds pressure of the column would
completely balance the atmospheric pressure, and the water would not
rise above the level, A.
TABLES AND
DATA
[Illustration: FIG. 675.]