A. On approaching the station where a stop is to be made, firing should be stopped far enough back to allow the carbon gases to be consumed before the throttle is closed, so there will be little or no black smoke from the stack and yet have sufficient fire that it will not be necessary to feed the fire again if a short stop is to be made until the train is started and the engine cut back or nearly to the running cut-off.
40. Q. How should you build up the fire when at stations in order to avoid black smoke?
A. Put in small quantities of coal at a time, have the door slightly open and have the blower on lightly; good judgment must be exercised by the fireman.
41. Q. Why is it that if there is a thin fire with a hole in it the steam pressure will fall at once?
A. Because too much cold air is drawn into the fire-box and through the tubes, retarding combustion and cooling the fire-box and tubes.
42. Q. If the injector is to be used after throttle is shut off, how should the fire be maintained?
A. A sufficient quantity of coal should be placed on the grates to maintain the maximum steam pressure and the blower used to keep the fire burning brightly.
43. Q. What would be the result of starting a heavy train or allowing drivers to slip with the fire too thin on the grates?
A. The fire would be pulled off the grates and into the tubes, leaving the fire bed full of holes and some of the fire remaining on the grates turned over. Large quantities of cold air would be drawn in, resulting in a rapid decrease of temperature and pressure. The tubes would possibly start leaking and the fire would be in such condition that it could not be built up properly in a long distance. Possibly the grates would become clogged up with green coal—an excellent opportunity for forming clinkers. In this condition, the engine would fail to make steam for the entire trip.
44. Q. Where should the coal, as a rule, be placed in the fire-box?