_This consists, in its most simple form, of a steam nozzle, the end of
which extends somewhat into the second nozzle, called the combining or
mixing nozzle; this connects with, or rather terminates in, a third
nozzle or tube, termed “the forcer.”_ At the end of the _combining
tube_, and before entering the forcer, is an opening connecting the
interior of the nozzle at this point with the surrounding space. This
space is connected with the outside air through a check valve, opening
outward in the automatic injectors, and by a valve termed the overflow
valve. The injector nozzles are tubes, with ends trumpet mouthed to
receive and deliver the fluids with the least possible loss by friction
and eddies.
As a thermodynamical machine, the injector is nearly perfect, since all
the heat received by it is returned to the boiler, except a very small
part which is lost by radiation; consequently its thermal efficiency
should be in every case nearly 100 per cent.
NOTE.—The operation of the injector is based on the fact, first
demonstrated by Giffard, that the motion imparted by a jet of steam
to a surrounding column of water is sufficient to force it into the
boiler from which the steam was taken, and, indeed, into a boiler
working at a higher pressure. The steam escaping from under pressure
has, in fact, a much higher velocity than water would have under
the same pressure and condition. The rate of speed at which steam
travels—taking it at an average boiler pressure of sixty pounds—when
discharged into the atmosphere, is about 1,700 feet per second. When
discharged with the full velocity developed by the boiler pressure
through a pipe, say an inch in diameter, the steam encounters the
water in the combining chamber. It is immediately condensed and
its bulk will be reduced say 1,000 times, but its velocity remains
practically undiminished. Uniting with the body of water in the
combining tube, it imparts to it a large share of its speed, and the
body of water thus set in motion, operating against a comparatively
small area of boiler pressure, is able to overcome it and flow into
the boiler. The weight of the water to which steam imparts its
velocity gives it a momentum that is greater in the small area in
which its force is exerted than the boiler pressure, although its
force has actually been derived from the boiler pressure itself.
[Illustration: FIG. 513.—See page 252.]
[Illustration: FIG. 514.—See page 251.] All injectors are similar in
their operation. They are designed to bring a jet of live steam from
the boiler in contact with a jet of water so as to cause it to flow
continuously in the direction taken by the steam, the velocity of which
it in part assumes, back into the boiler and against its own pressure.
There are three distinct types of live steam injectors, the “simple
fixed nozzle,” the “adjustable nozzle,” and the “double.” The first has
one steam and one water nozzle which are fixed in position but are so
proportioned as to yield good results. There is a steam pressure for
every instrument of this type at which it will give a maximum delivery,
greater than the maximum delivery for any other steam pressure either
higher or lower.
The second type has but one set of nozzles, but they can be so adjusted
relative to each other as to produce the best results throughout a long
range of action; that is to say, it so adjusts itself that its maximum
delivery continually increases with the increase of steam pressure. The
third type, double injectors, are those in which the delivery from one
injector is made the supply of a second, and they will handle water at
a somewhat higher temperature than single ones with fixed nozzles. The
double injector makes use of two sets of nozzles, the “_lifter_” and
“_forcer_.” The lifter draws the water from the reservoir and delivers
it to the forcer, which sends it into the boiler. All double injectors
have fixed nozzles.
The action of the injector is as follows: Steam being turned on, it
rushes with great velocity through the steam nozzle into and through
the combining tube. This action causes air to flow from the suction
pipe, which is connected to the combining tube, with the result that
more or less vacuum is formed, thus inducing a flow of water.
NOTE.—_The motive force of the injector is found in the heat received
from the steam._ The steam is condensed and surrenders its latent
heat and some of its sensible heat. The energy so given up by each
pound of steam amounts to about 900 thermal units, each of which
is equivalent to a mechanical force of 778 foot pounds. This would
be sufficient to raise a great many pounds of water against a very
great pressure could it be so applied, but a large portion of it
is used simply to heat the water raised by the injector. The above
explanation will apply to every injector in the market, but ingenious
modifications of the principles of construction have been devised in
order to meet a variety of requirements.
[Illustration: FIG. 515.—See page 252.]
[Illustration: FIG. 516.—See page 252.]
After the water commences to flow into the injector it receives motion
from the jet of steam; it absorbs heat from the steam and finally
condenses it, and thereafter moves on through the forcer tube simply
as a stream of water, at a low velocity compared with that of the
steam. At the beginning of the forcer tube, it is subjected only to
atmospheric pressure, but from this point the pressure increases and
the water moves forward under a diminished velocity.
That the condensation of the steam is necessary to complete the process
will be evident, for if the steam were not condensed in the combining
chamber, it would remain a light elastic body and, though moving at
high speed, would have a low degree of energy.
Some injectors are given special names by their makers, such as
ejectors and inspirators, but the term injectors is the general name
covering the principle upon which all these devices act. The exhaust
steam injector is a type different from any of the above-named, in that
it uses the exhaust steam from a non-condensing engine. Exhaust steam
represents fourteen and seven-tenths (14.7) pounds of work, and when
the steam entering the injector is condensed the water is forced into
the boiler upon the same general principle as in all injectors.
The injector can be, and frequently is, used as a pump to raise water
from one level to another. It has been used as an air compressor,
exhauster and also for receiving the exhaust from a steam engine,
taking the place, in that case of both condenser and air pump.
The injector is not an economical device, but it is simple and
convenient; it occupies a very small space, is not expensive and
entirely free from severe strains on its durability; moreover, where a
number of boilers are used in one establishment, it is very convenient
to have the feeding arrangements separate, so that each boiler may be a
complete generating system in itself and independent of its neighbors.
_The following text_ is intended to describe the instruments
illustrated on pages 244, 246, 248 and 250.
[Illustration: FIG. 517.]
[Illustration: FIG. 518.]
_The “Manhattan” automatic injector_ is shown in perspective and
outline upon page 244. This instrument is made by Messrs. Schaeffer &
Budenberg of New York City.
This injector is designed for portable and semi-portable engines and
boilers, and is also adapted for stationary boilers _requiring no high
lift_. Its main features are simplicity and positive automatic action.
It works under pressures ranging from 30 to 150 lbs., either lifting or
non-lifting.
The letters in the outline cut refer to the parts:
_a._ Steam Nozzle.
_b._ Combining Nozzle with Flap.
_c._ Delivery Tube.
_d._ Screw Cap.
_e._ Cap Screw for Overflow.
_f._ Overflow Valve.
_g._ Tail Pipe.
_h._ Tail Pipe Nut.
_The “Peerless” automatic injector_ is shown on page 246. This is, in
effect, the same instrument as the “Manhattan” except it has a steam
spindle with handle to regulate the flow of steam. See figure 514.
Two classes of Peerless injectors are made, viz.:
Class A—for high pressures ranging from 50 to 200 pounds.
„ B— „ low „ „ „ 20 to 80 „
and they are stamped accordingly.
They are adapted for any service requiring the lifting of water.
Class A is made for lifts up to 12 feet.
„ B „ „ „ 8 „
but if so ordered, they can be arranged for higher lifts. They may also
be used as non-lifting injectors.
The temperatures of feed water taken by these injectors, if non-lifting
or at a low lift, can be as follows:
PRESSURE.
35 to 45 50 to 85 90 105 lbs.
TEMPERATURE.
144 to 136 133 to 130 129 122° F.
PRESSURE.
120 135 150 lbs.
TEMPERATURE.
118 to 113 109 to 105 104 to 100° F.
The spindle acts as a valve for the steam inlet; an extra seam valve is
therefore not absolutely required, but recommended for convenience of
detachment.
The letters in Figs. 520-533, page 254, relate to the names of “the
parts” of the Peerless injector.
_a._ Steam Nozzle.
_b._ Combining Nozzle with Flap.
_c._ Delivery Tube.
_e._ Cap Screw for Overflow.
_f._ Overflow Valve.
_g._ Tail Pipe.
_h._ Tail Pipe Nut.
_j._ Screw Plug with Stuffing-Box.
_k._ Follower Nut on Plug j.
_l._ Packing Sleeve to j.
_m._ Steam Spindle.
_n._ Crank to Spindle m.
_o._ Screw Nut to Spindle m.
_p._ Handle to Crank n.
_The Monitor injector_, Fig. 513, page 246, was designed originally for
locomotive work. It consists mainly of two parts, viz., 1, the lifting
device which raises the water into the injector and, 2, the forcing
device which “picks up” the water and causes it to flow into the boiler.
_The Metropolitan double tube injector_ is shown in the two figures on
page 248.
These are made by the Hayden & Derby Mfg. Co. This instrument is of
the double-tube design and in that particular resembles the Korting
injector described on page 264. Both the lifting and forcing, as well
as the overflow valves are controlled by one handle.
_The Metropolitan single tube injector_ is represented by the Figs. 517
and 518, page 250. The internal parts of this injector, as may be seen
from the sectional engraving, are stationary. The steam is regulated
by the handle, K, which is attached to the stem, M; the water supply
adjusts itself automatically.
_The capacity of the leading injectors_ is nearly the same under
similar working conditions as represented by the following