With cold feed water, a good injector with a two foot lift ought to
start with 25 pounds pressure and work up to I50 pounds. With 8 foot
lift, ought to start at 30 pounds and work up to I30. With feed water
heated to I00 degrees Fahrenheit it should start with the same lift,
that is, will say 2 foot, at 26 and work Up to I20, and at 8, from 33 up
to I00. You will see by this that conditions, consisting of variation of
temperature in the feed water and different lifts, change the efficiency
of your injector very materially, and the water can soon get beyond the
ability of your injector to work at all. The above refers more
particularly to the single tube injector. The double tube injector
under the same conditions as above should work from I4 pounds to 250,
and from I5 to 2I0, but as this injector is not generally used on farm
engines you will most likely not meet with it very often.
The injector should not be placed too near the boiler, as the heat from
it will make it difficult to start the injector each time after it has
been standing idle.
If the injector is so hot that it will not lift the cold water, there is
no way of cooling it except by applying the water on the outside. This
is most effectively done by covering the injector with a cloth and
pouring water over the cloth. If, after the injector has become cool,
it still refuses to work, you may be sure that there is some obstruction
in it that must be removed. This can be done by taking off the cap, or
plug-nut, and running a fine wire through the cone valve or cylinder
valve. The automatic injector requires only the manipulation of the
steam valve to start it. There are other makes that require, first: that
the injector be given steam and then the water. To start an injector
requires some little tact, (and you will discover that tact is the
handiest tools you can have to make you a good engineer). To start an
injector of the Pemberthy type; first give it sufficient steam to lift
the water, allowing the water to escape at overflow for a moment or long
enough to cool the injector, then with a quick turn shut off and open up
the supply which requires merely a twist of the wrist.
If the injector fails to take hold at once don't get ruffled but repeat
the above move a few times and you will soon start it, and if you have
tact, (it is only another word for natural ability) you will need no
further instructions to start your injector. But remember that no
injector can work coal cinders or chaf and that all joints must be air
tight. Don't forget this.
It is now time to give some attention to the heater. While the heater
is no part of the pump, it is connected with it and does its work
between the two horizontal check valves. Its purpose is to heat the
water before it passes into the boiler. The water on its way from the
pump to the boiler is forced through a coil of pipes around which the
exhaust steam passes on its way from the cylinder to the exhaust nozzle
in the smokestack.
The heaters are made in several different designs, but it is not
necessary to describe all of them, as they require little attention and
they all answer the same purpose. The most of them are made by the use
of a hollow bedplate with steam fitted heads or plates. The water pipe
passes through the plate at the end of the heater into the hollow
chamber, and a coil of pipes is formed, and the pipe then passes back
through the head or plate to the hot water check valve and into the
boiler.
The steam enters the cylinder from the boiler, varying in degrees of
heat from 300 to 500. After acting on the piston head, it is exhausted
directly into the chamber or hollow bed-plate through which the pipes
pass. The water, when it enters the heater, is as cold as when it left
the tank, but the steam which surrounds the pipes has lost but little of
its heat, and by the time the water passes through the coil of pipes it
is heated to nearly boiling point and can be introduced into the boiler
with little tendency to reduce the steam. This use of the exhaust steam
is economical, as it saves fuel, and it would be injurious to pump cold
water directly into a hot boiler.
If your engine is fitted with both cross head pump and injector, you use
the injector for pumping water when the engine is not running. The
injector heats the water almost as hot as the heater. If your engine is
running and doing no work, use your injector and stop the pump, for,
while the engine is running light, the small amount of exhaust steam is
not sufficient to heat the water and the pressure will be reduced
rapidly. You will understand, therefore, that the injector is intended
principally for an emergency rather than for general use. It should
always be kept in order, for, should the pump refuse to work, you have
only to start your injector and use it until such time as you can remedy
the trouble.
We have now explained how you get your water supply. You understand that
you must have water first and then fire. Be sure that you have the
water supply first.