47. Q. If upon opening the fire-box door you discover there what is
commonly called a red fire, what might be the cause?

A. The grates may have become clogged with ashes or clinkers so that
sufficient air could not pass through them to the fire.

48. Q. Is it not a waste of fuel to open the fire-box door to prevent
pops from opening? How can this be prevented more economically?

A. Yes. This can usually be prevented by putting the heater into the
tank, or putting on the injector, or by more careful firing.

49. Q. Describe the principle upon which the injector works.

A. The action of the injector is due first to the difference between
"kinetic" or moving energy and "static" or standing energy; second, to
the fact that steam at a pressure travels at a very high velocity and
when placed in contact with a stream of water it is condensed into
water, and at the same time it imparts enough velocity to the water to
give it sufficient momentum to overcome a pressure even greater than the
original pressure of the steam. By imparting this velocity to the water
it gives it sufficient energy to throw open the check valves and enter
the boiler against high pressure.

50. Q. What is the difference between a lifting and a non-lifting
injector?

A. A lifting injector will create sufficient vacuum to raise the water
from the level of the tank. The steam tubes in a non-lifting injector
are different and it will not raise the water, but merely force it into