It is a fact that
with all injectors as the vertical distance the injector lifts is
increased, it requires a greater steam pressure to start the injector,
and the highest steam pressure at which the injector will work is
greatly decreased. If the feed water is heated, a greater steam
pressure is required to start the injector and it will not work with as
high steam pressure. The capacity of an injector is always decreased as
the lift is increased, or the feed water heated. To obtain the most
economical results the proper sized injector must be used. When the
exact quantity of water consumed per hour is known it can be easily
determined from the capacities given in the price lists which sized
injector must be selected.
An injector must always be selected having a maximum capacity in excess
of the water consumed. If the exact amount of water consumed per hour
is not known, and cannot be easily determined, the proper size can be
approximately determined from the nominal H. P. of the boiler. The
usual custom has been to allow 7 I/2 gallons of water per hour, which is
a safe rule for the ordinary type of boiler.
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