he diaphragm and the draft pipes or petticoat
pipe.

41. Q. What object is there in having the exhaust steam go through the
stack?

A. To create a draft through the tubes and fire-box.

42. Q. How does this affect the fire?

A. The exhaust steam escaping through the stack tends to empty the
smoke-box of gases and produces a partial vacuum there, atmospheric
pressure then forces air through the grates and tubes to refill the
smoke-box, and in this way the draft through the fire is established and
maintained.

43. Q. Explain what adjustments can be made and the effect of each
adjustment on the fire.

A. Larger or smaller nozzle tips cause less or greater draft on the
fire; raising or lowering the draft pipes and diaphragm causes the
engine to burn the fire more at the rear or front end of the fire-box;
the size and position of the draft pipes increase the draft through the
top or bottom flues; the latter adjustments should always be attempted
before reducing the nozzle.

44. Q. What does it indicate when the exhaust issues strongest from one
side of the stack?

A. The stack, exhaust pipe or petticoat pipe are out of plumb.

45. Q. What is the effect of leaky steam pipe joints inside the
smoke-box?

A. The engine will not steam freely.

46. Q. What causes "pull" on the fire-box door?

A. The partial vacuum in the front end; when excessive it indicates
dampers closed, fire clinkered or insufficient opening for the admission
of air under the fire.

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 press