_INJECTORS._
Injectors have made remarkably rapid strides into public favor during
the last ten years. It is a safe prediction to say, that, before the
end of another decade, there will be no new pumps put upon locomotives.
So long as injectors were imperfectly understood, and were used with no
regularity, they retained the name of being unreliable; but, so soon as
they began to be made the sole feeding-medium for locomotive boilers,
they had to be worked regularly, and kept in order, which quickly made
their merits recognized.
INVENTION OF THE INJECTOR.
The feed injector was invented by Henri Giffard, an eminent French
scientist and æronaut. Its successful action was discovered during a
series of experiments made with the view of devising light machinery
that might be used to propel balloons. Although Giffard designed the
most perfect balloon that was ever constructed, the injector was not
used upon it; and the invention was laid aside, and almost forgotten.
During the course of a sea-voyage, Giffard happened to meet Stewart of
the engineering firm, Sharp, Stewart, & Co., of Manchester, England.
In the course of a conversation on the feeding of boilers, Giffard
remembered his injector, and mentioned its method of action. Stewart
was struck with the simplicity of the device, and undertook to bring
it out in England, which he shortly afterwards did, representing the
interests of the inventor so long as the original patents lasted. By
his advice, William Sellers & Co. of Philadelphia were given control of
the American patents.
Seldom has an invention caused so much astonishment and wild
speculation among mechanics, and even among scientists, as the
injector did for the first few years of its use. Scientists were not
long in discovering the philosophy of the injector’s action, but that
knowledge spread more slowly among mechanics. It was regarded as a case
of perpetual motion,--the means of doing work without power, or, as
Americans expressed it, by the same means a man could raise himself by
pulling on his boot-straps.
TRYING TO FIND OUT HOW THE INJECTOR WORKED.
Among the mechanics I associated with, the injector was spoken of as
a machine having a secret method of action. There was supposed to be
some part inside, where a vacuum was formed, which sent the water into
the boiler. We were all familiar with the vacuum of condensing engines,
and it was a convenient solution of the mystery. I remember committing
what we regarded as a heinous sin, in trying to find out the secret
of the injector. On a Sunday forenoon in a Scotch town, where it was
considered next to a crime to miss going to church, three of us stole
quietly into an engine-house, and took an injector apart, when we knew
the foreman, like a pious man, was listening to the sermon. All our
plans had been laid the previous day, and the necessary tools laid
conveniently at hand. The feeling of disappointment we experienced at
finding nothing to explain the working of the thing, is still vivid in
my memory.
THE PRINCIPLE OF THE INJECTOR’S ACTION.
The principle of the injector’s action is that of induced currents,
which is much more popularly understood to-day than it was twenty-five
years ago. A current of any kind has a tendency to induce a movement in
the same direction of any body it passes over or touches. Thus, we are
all familiar with the fact that a current of air called wind, passing
over the surface of a body of water, sets waves in motion, and dashes
the water high up on the shore above its original level. In the same
way, a jet of steam moving very rapidly, when injected into a body of
water under favorable conditions, imparts a portion of its motion, and
starts momentum sufficient to overcome the original pressure of the
steam. That is how the injector is made to force water into a boiler
against the same pressure the steam is starting from. The principle
is now utilized in the arts for many useful purposes. The ordinary
locomotive blast, blowers, steam siphons, steam-jets, jet exhausters,
and argand burners, are common instances of its application.
When the action of the injector is closely examined, its mystery as
a source of power disappears; for it is found that an amount of heat
equal to the mechanical equivalent of work done, is used up during the
operation of feeding. Thus, when a given quantity of heat units pass
from the throttle to work the injector, the whole of the heat does not
return to the boiler along with the feed-water, as was first supposed
to be the case; but a portion of heat representing the foot pounds of
work done is dissipated, besides other losses incident to leakage,
radiation, and convection.
DIFFERENT FORMS OF INJECTOR.
There are a great many different forms of injectors in use, but all of
them conform to certain elementary principles in their mode of action.
Steam passes from the boiler through the steam-pipe and receiving-tube
_A_ (Fig. 1) at a high velocity, and, combining with the water at the
point _B_, condenses, but imparts considerable momentum to the water,
which rushes along into the delivery pipe, raises the check-valve, and
passes into the boiler.
[Illustration: FIG. 1.]
The tubes of the injector are arranged so that a concentrated jet of
steam shall impinge upon the water to force it through passages that
are designed in the best form for maintaining the solidity of the
current. The speed imparted to the water represents the work performed
by the steam, and upon this velocity depends the successful action
of the injector. As the current of water for starting the injector
could not be induced against the constant pressure on the check-valve,
which equals the pressure at the throttle, an overflow is provided
where the water can flow unchecked till the necessary momentum is
obtained, when the overflow is closed. All deviations in construction
from the elementary injector shown in Fig. 1 are made for the purpose
of extending the action of the injector under varied conditions, for
making it work automatically under different pressures of steam, and
for improving its capacity to lift water above its natural level.
A HEATER-PIPE ACTING AS AN INJECTOR.
Before the invention of the injector, cases occasionally happened of
the heater-pipe acting as an injector. Where the end of the heater pipe
was carried through the feed-pipe, and pointed towards the check-valve,
starting the heater under favorable conditions would carry the water
into the boiler. A great many old engineers relate instances where this
has happened.
SKILL AND REFLECTION NEEDED IN REPAIRING INJECTORS.
Injectors can be kept in good order with less work than is needed
to keep a pump going, but the highest kind of mechanical skill is
required for the injector when repairs must be done. Almost any kind
of machinist can fit a new chamber or plunger into a pump. Many men
who will do this job satisfactorily will get badly left when they
try to put a defective injector in order. To do such work, thoughtful
reflection is called for, besides the hand that can do accurate
fitting. A workman who may be good on guides or cross-heads or links,
takes an injector apart that will not work, and can perceive nothing
wrong with it, because he has not got the philosophy of the thing
through his head; and he must have that before he can have insight into
the probable cause of derangement.
CARE OF INJECTORS.
When an engineer finds that an injector refuses to work, his first
resort should be the strainer. That gets choked with cinders or other
impurities so frequently, that no time should be lost in examining
it. One day, when I was running a round-house, an engineer came in
breathless, with the information that his engine was blocked in the
yard, and he must dump his fire, as he could not get his injector to
work. The thermometer stood at twenty degrees below zero, and an Iowa
blizzard was blowing; so the prospect of a dead engine in the yard
meant some distressingly cold labor. I asked, the first thing, if he
had tried the strainer; and his answer was, that the strainer was all
right, for the injector primed satisfactorily, but broke every time he
put on a head of steam. I went out to the engine, and had the engineer
try to work the injector. By watching the overflow stream, I easily
perceived that the injector was not getting enough water, although it
primed. An examination showed that the strainer was full of cinders,
and the injector went to work all right when the obstruction to the
water was removed.
THE MOST COMMON CAUSES OF DERANGEMENT.
Sand and cinders are the greatest cause of failures with injectors; as
they are, indeed, with all water-feeding apparatus. I knew a case where
water for a locomotive, running on a short branch, was taken out of
a sandy creek with a siphon. The tank had generally about six inches
of sand in the bottom. The engine had a pump and an injector; but all
the feeding had to be done by the latter, for the pump never worked a
gallon of water. The injector worked the water through when it seemed
a quarter sand. In a short time the sand destroyed the tubes of the
injector, for it acted on them the same way as a sand-blast does in
cutting files or glass.
A very common cause of failure of injectors, is leakage of steam
through throttle-valve or check-valve, keeping the injector so hot that
no vacuum can be formed to make it prime. A great many injector-checks
have been turned out too light for ordinary service, while others are
made in a shape that will always leave the valve away from the seat
when they stop working. Then the engineer has to run forward, and pound
the check with a hammer to keep the steam from blowing back; and that
soon ruins the casting. Check-valves set in a horizontal position are
worthless with water that contains grit.
HOW TO KEEP AN INJECTOR IN GOOD ORDER.
To preserve a good working injector, the engineer should see that all
the pipes and joints are kept perfectly tight. It is hard to keep
pipes and joints tight when they are subjected to the continual jars
a locomotive must stand; but injectors can not be depended on where
there is a possibility of air mixing with the water. Leaky joints
or pipes are particularly troublesome to lifting injectors; for air
passes in, and keeps the steam-jet from forming a vacuum. At first
the injector will merely be difficult to start; but, as the leaks
get worse, there will be no starting it at all. Then, the air mixing
with the water is detrimental to the working of all injectors, as its
tendency is to decrease the speed of the water. The compact molecules
of water form a cohesive body, which the steam can strike upon with
telling force to keep it in motion. When the water is mixed with
air, it lacks the element of compactness; and the steam-jet strikes
a semi-elastic body, which does not receive momentum readily. This
mixture of steam and air does not act solidly on the check-valve, but
makes the water pass in with a bubbling sound, as if the valve were
moving up and down; and the stream of water breaks very readily when it
is working in this way.
CURIOUS CASES OF TROUBLE WITH AN INJECTOR.
I ran a Sellers improved injector on a locomotive about a year, and it
was an excellent feeding apparatus; but I several times had curious
cases of trouble in getting it to work. Once it began drawing air;
and I could not find out where the air was coming from, for the pipes
seemed all tight. But the air was going through, for I could hear its
mutterings; and the water kept breaking, which was an annoyance on
the road. A heater-pipe was attached to the injector feed-pipe; and I
afterward found out that the air was getting in at the top joint of
this pipe, which did not show a leak, being above the water.
Another time I had almost a failure with this injector out in the snow.
I was out with a snow-plow, opening the road through enormously deep
snow-drifts. We had worked on one bank for several days; and we made
water by shoveling snow into the tank, which was melted by blowing
steam through the heaters and injector. Cinders were passed into the
tank very freely with the snow, and presently I began to have trouble
with my injector. I took it apart several times, and cleaned out
cinders, when it went to work all right again. But a time came when it
refused to work when there were no cinders inside, and it seemed that
no amount of coaxing would make it start. It would prime all right;
but, so soon as I gave it steam, the water would break. Driven to my
wits’ end, I made the fireman try to work the injector, while I went
down and watched its action. Everything seemed tight: I had examined
the strainer, and there appeared no reason why it should not operate as
well as it ever did. While watching it, I saw a drop of water oozing
out at the stem of the overflow-valve; but I reasoned, “That can not
affect the working of the injector, because it is ahead of where the
water starts.” But, seeing that the thing would persist in not working,
I put a bit of packing in the overflow-stem, thinking it will do no
harm any way; and then the injector went to work all right, and I had
no more trouble with it. So a defect that may seem trifling, sometimes
proves serious to an injector.
COMMON DEFECTS.
As maintaining unbroken speed on the water put in motion is the first
essential in keeping an injector in good working-order, any thing
that has a tendency to reduce that speed will jeopardize its action.
A variety of influences combine to reduce the original efficiency
of an injector. Those with fixed nozzles are constructed with the
orifices of a certain size, and in the proportion to each other which
experiment has demonstrated to be best for feeding with the varied
steam-pressures. When these orifices get worn out of the proper size,
the injector will work badly; and nothing will cure it but new tubes.
The tubes sometimes get loose inside the shell of the injector, and
drop down out of line. The water will then strike against the side of
the next tube, or on some point out of the true line, scattering it
into spray, which contains no energy to force itself into the boiler. A
machinist examining a defective injector, should always make sure that
the tubes are not loose. Injectors that suffer from this defect will
not work without a high pressure of steam. Injectors suffering from
incrusted water-passages will generally work best with the steam low.
Cases of the latter kind are common in calcareous districts. I have
known instances where injectors got so incrusted with lime that the
passages were almost closed.
Joints about injectors that are kept tight by packing must be closely
watched. Many an injector that failed to work satisfactorily has been
entirely cured by packing the ram-gland.
CARE OF INJECTORS IN WINTER.
During severe frosty weather, an injector can be kept in order much
easier than a pump; but it needs constant watching and intelligent
supervision.
To keep an injector clear of danger from frost, it should be fitted up
so that all the pipes can be thoroughly drained, by frost-cocks put in
for that purpose. Bends in the pipes, where water could stand, should
be avoided as far as possible; and, where they can not be avoided, the
lowest point should contain a frost-cock.
To run an injector successfully, thoughtful care is requisite on the
part of the engineer; and, where this is given, the injector will prove
itself a very economical boiler-feeder.
SELLERS INJECTOR.
When the Giffard injector was first introduced into this country,
by William Sellers & Co., Philadelphia, it was a very defective
boiler-feeder; but that firm effected great improvements, and led the
way for making the injector the popular boiler-feeder it is to-day.
They made the instrument self-adjusting, and improved its design,
so that it would automatically feed, however much the pressure of
the boiler varied. After numerous changes, the injector of 1876 was
produced, which is shown by a sectional view in Fig. 2. The Sellers
injector of to-day remains substantially the same as it was when
exhibited at the Centennial Exposition.
[Illustration: FIG. 2.]
Referring to Fig. 2, _A_ is the receiving-tube, which will be closed
to the admission of steam by the valve _X_. A hollow spindle passing
through the receiving-tube into the combining-tube, is secured to the
rod _B_; and the valve _X_ is fitted to this spindle in such a way,
that the latter can be moved a slight distance (until the stop shown in
the figure engages with valve _X_) without raising the valve _X_ from
its seat. A second valve, _W_, secured to the rod _B_, has its seat
in the upper side of the valve _X_, so that it can be opened (thus
admitting steam to the center of the spindle) without raising the valve
_X_ from its seat, if the rod _B_ is not drawn out any farther, after
the stop on the hollow spindle comes in contact with the valve _X_.
_D_ is the delivery-tube, _O_ an overflow opening into space _C_, _K_
the check-valve in delivery-pipe, and _P R_ the waste-valve. The upper
end of the combining-tube has a piston _N N_ attached to it, capable
of moving freely in a cylindrical portion of the shell _M M_; and the
lower end of the combining-tube slides in a cylindrical guide formed in
the upper end of the delivery-tube.
The rod _B_ is connected to a cross-head, which is fitted over the
guide-rod _J_; and a lever _H_ is secured to the cross-head. A rod _L_,
attached to a lever on the top end of the screw waste-valve, passes
through an eye that is secured to the lever _H_; and stops _T_, _Q_,
control the motion of this rod, so that the waste-valve is closed when
the lever _H_ has its extreme outward throw, and is opened when the
lever is thrown in so as to close the steam-valve _X_; while the lever
can be moved between the positions of the stops _P_, _Q_, without
affecting the waste-valve. A latch _V_ is thrown into action with teeth
cut in the upper side of the guide-rod _J_, when the lever _H_ is drawn
out to its full extent, and then moved back; and this click is raised
out of action as soon as it has been moved in far enough to pass the
last tooth on the rod _J_. An air-vessel is arranged in the body of
the instrument, as shown in the figure, for the purpose of securing
a continuous jet when the injector and its connections are exposed
to shocks, especially such as occur in the use of the instrument on
locomotives.
The manipulation required to start the injector is exceedingly
simple,--much more so in practice, indeed, than it can be rendered in
description. Moving the lever _H_ until contact takes place between
valve _X_ and stop on hollow spindle, which can be felt by the hand
upon the lever, steam is admitted to the center of the spindle, and,
expanding as it passes into the delivery-tube _D_ and waste-orifice
_P_, lifts the water through the supply-pipe into the combining-tube
around the hollow spindle, acting after the manner of an ejector or
steam-siphon. As soon as solid water issues through the waste-orifice
_P_, the handle _H_ may be drawn out to its full extent, opening the
steam-valve _X_, and closing the waste-valve, when the action of the
injector will be continuous as long as steam and water are supplied to
it.
THE NATHAN MANUFACTURING COMPANY’S MONITOR INJECTOR.
[Illustration: FIG. 3.]
One of the most successful and enduring injectors in use is the
Monitor, the distinguishing feature of which is, that the injector is
constructed with fixed nozzles, that insure great durability, combined
with certainty of action. The Monitor injector is shown in section in
Fig. 3. To start the injector, the middle cock is opened, which is
the lifting-jet. When water appears at the overflow, the steam-valve
is opened, and the lifting-jet closed. The work of the injector is
regulated by the lazy-cock, which is the bottom handle. A movable
valve, operated by an eccentric on the stem, is now employed as a
lazy-cock; a common cock having been found troublesome during frosty
weather. The combining-tube is attached to the line-check, and can be
taken out with the check, which provides an easy means of effecting
examination or repairs.
THE KORTING INJECTOR.
[Illustration: FIG. 4.]
An examination of Fig. 4 will show that this injector is a double-tube
instrument; the first tube being proportioned for raising and
delivering the water under pressure to the second one, which
completes the operation of forcing the water into the boiler. This
arrangement enables the injector to be worked through a wide range of
steam-pressures without any adjustment of parts. By making the first
tube proportionately small, a high power of suction is obtained,
which enables the injector to feed water of such high temperature
that it may be delivered into the boiler above the boiling-point. The
Korting injector is operated entirely by one handle, and requires no
instruction to teach its working. The feed is regulated by the patent
combined regulation-valve and dirt-stop, which regulates the supply of
water, and prevents the possibility of dirt reaching the injector.
THE HANCOCK INSPIRATOR.
[Illustration: FIG. 5.]
Fig. 5 gives a cross-section of the Hancock inspirator. It consists
essentially of a lifting-jet and lifting-nozzle, combined with a
forcing-jet and force-nozzle or injector; steam being admitted to both
of these nozzles whenever the inspirator is working, to deliver the
supply-water to the force-nozzle, and to force it through the nozzle
into the boiler. Although both the lifting and forcing nozzles are
fixed, their proportion, one to the other, is such that the inspirator
requires no adjustment for changes in steam-pressure or water-supply;
the waste-valve being kept closed while the instrument is in operation,
except at the time of starting. The duplex nozzle arrangement of the
Hancock inspirator enables that instrument to feed water of high
temperature. In this respect it will act as well as the ordinary pump,
besides having all the advantages of an injector. A form of inspirator
is made specially for locomotive service, which is operated by a single
handle.