747. Q.—­In starting from a station, what precautions should be observed with respect to the feed?

A.—­In starting from a station, and also in ascending inclined planes, the feed water is generally shut off; and therefore before stopping or ascending inclined planes, the boiler should be well filled up with water.  In descending inclined planes an extra supply of water may be introduced into the boiler, and the fire may be fed, as there, is at such times a superfluity of steam.  In descending inclined planes the regulator must be partially closed, and it should be entirely closed if the plane be very steep.  The same precaution should be observed in the case of curves, or rough places on the line, and in passing over points or crossings.

748. Q.—­In approaching a station, how should the supply of water and fuel be regulated?

A.—­The boiler should be well filled with water on approaching a station, as there is then steam to spare, and additional water cannot be conveniently supplied when the engine is stationary.  The furnace should be fed with small quantities of fuel at a time, and the feed should be turned off just before a fresh supply of fuel is introduced.  The regulator may, at the same time, be partially closed; and if the blast pipe be a variable one, it will be expedient to open it widely while the fuel is being introduced, to check the rush of air in through the furnace door, and then to contract it very much so soon as the furnace door is closed, in order to recover the fire quickly.  The proper thickness of coke upon the grate depends upon the intensity of the draught; but in heavily loaded engines it is usually kept up to the bottom of the fire door.  Care, however, must be taken that the coke does not reach up to the bottom row of tubes so as to choke them up.  The fuel is usually disposed on the grate like a vault; and if the fire box be a square one, it is heaped high in the corners, the better to maintain the combustion.

749. Q.—­How can you tell whether the feed pumps are operating properly?

A.—­To ascertain whether the pumps are acting well, the pet cock must be turned, and if any of the valves stick they will sometimes be induced to act again by working with the pet cock open, or alternately open and shut.  Should the defect arise from a leakage of steam into the pump, which prevents the pump from drawing, the pet cock remedies the evil by permitting the steam to escape.

750. Q.—­What precautions should be taken against priming in locomotives?

A.—­Should priming occur from the water in the boiler being dirty, a portion of it may be blown out; and should there be much boiling down through the glass gauge tube, the stop cock may be partially closed.  The water should be wholly blown out of locomotive boilers three times a week, and at those times two mud-hole doors at opposite corners of the boiler should be opened, and the boiler be washed internally by means of a hose.  If the boiler be habitually fed with dirty water, the priming will be a constant source of trouble.