Locomotive Engine Running and Management

by Angus Sinclair

PETTICOAT-PIPE.

The petticoat-pipe performs, in relation to draught, functions of a similar nature to those performed by the tubes of an injector in inducing the flow of water; and its efficiency is reduced by the same disturbing agencies. The pipe must have a size in proportion to the diameter of stack, and it must be set so that it shall deliver the exhaust-steam to make a straight shoot through the stack. When these conditions are properly arranged, the exhaust-steam goes through the stack like a piston, leaving a vacuum behind. The petticoat-pipe is a device confined mainly to American locomotives; and its purpose is to regulate the draught in the smoke-box so that the currents of hot gases are drawn uniformly through the flues, the top, bottom, and sides getting about the same heating intensity as passes through the middle rows. The opportunity for the exhibition of good firing depends greatly upon the petticoat-pipe being constructed properly, and secured at the right position. It is impracticable to lay down a positive rule for dimensions and best position of these pipes, for engines of the same proportions frequently require different petticoat-pipe arrangements to make them steam freely. For our 17 × 24 engine, there is a petticoat-pipe 11½ inches in diameter, with a flare, at bottom, 17 inches wide. The pipe reaches within 3 inches of the bottom of the stack, and is set one inch above the nozzle. This gives good results in our case. When engines with sufficient heating-surface do not steam freely, the trouble nearly always lies in malproportioned or badly set petticoat-pipes. Sometimes a very small change in the position of this pipe will have a wonderful effect upon the steaming qualities of the engine. If the pipe is set too high, most of the draught will pass through the lower flues; and the upper rows will become filled with soot, and many of them are likely to get choked with fine ashes, which remains there for want of draught to force it out. Should it be too low, the bottom rows of flues will suffer from the effect of defective draught. When the petticoat-pipe is just right, the flues will look uniformly clean inside, which can be ascertained by a close inspection of the smoke-box. In addition to making the engine lose the benefit of its full heating-surface, a badly arranged petticoat-pipe concentrates the draught so much that it tears the fire to pieces at one particular point; and the only resource for the man who wishes to keep up steam is to fire heavily, thereby preventing cold air from being drawn through the crevices. Many engines will not steam with a light fire, and yet do well with a heavy body of coal on the grates. In nearly every instance of this kind, the fault lies in the petticoat-pipe; and, if this is properly adjusted, the engine will be found capable of carrying a light fire, and will show far more economical results than could be reached with heavy firing. Some engineers assume that the petticoat-pipe must be right when an engine steams freely, even though a heavy fire is necessary to produce this result. This is a mistake. It may be badly set or badly proportioned, only a degree smaller than it is where the engine will not steam to keep the train going. By closely watching the action of the blast on the fire of an engine that calls for heavy firing, the engineer learns where the fault lies. When the engine is laboring on a hard pull, he should open the door; and if he finds, that, in a particular section of the fire-box, the smaller pieces of coal are dancing and glowing with an incandescence more brilliant than the other parts, and if he finds that this is repeatedly the case, he may conclude that the nozzles are too small, or the petticoat-pipe is working the mischief with his coal-account. Should the nozzles be the proper size, he had better lose no time in beginning to experiment with this pipe. He can lower it a quarter of an inch at a time, and mark the effects of the change on the fire. Should that produce no improvement, he may try raising it; or, if there is a movable sleeve on the top, that may be set in different positions. An engineer can test a petticoat-pipe much better by manipulating it on the road than in the round-house. If no change of position will improve the working of the pipe, one of different dimensions should be tried. Perseverance in this line will bring the right thing in the end. I knew an engineer who tried five different petticoat-pipes before the proper one was reached. Such a thing causes labor, and needs patience; but it pays when the fuel-account for running ten thousand miles comes in.