It is generally understood that an intermittent or recurring blow belongs to the pistons, and that a constant blow comes from the valves. But sometimes the valves blow intermittently, being tight at certain points of the travel, and leaky at other points. To distinguish between the character of these blows is sometimes a little difficult except to the thoroughly practiced ear. The sound of the blow can be heard best when the door is open, and the novice should not fail to listen for it under that condition. The valve blow is a sort of wheeze, with the suggestion of a whistle in it: the piston makes a clean, honest blow, which would break into a distinct roar if enough steam could get through. But a whistling sound in the exhaust is, by no means, a certain indication of the valves blowing through; for sometimes the nozzles get clogged up with a gummy substance from the lubricating oils, and a distinct whistling exhaust results therefrom. With a watchful ear, the progress of degeneration in the valves can be noted day after day; for it is a decay which goes on by degrees,—the inevitable slow destruction that friction inflicts upon rubbing surfaces. Pistons are more erratic in their calls for attention. With them it is quite common for a stalwart blow to start out without any warning, the cause generally being broken packing-rings. The various kinds of steam packing seem more liable to have broken rings than the old-fashioned spring packing, but they generally run longer with less attention.
ACCIDENTS PREVENTED BY ATTENDING TO THE NOTE OF WARNING FROM THE EXHAUST.
The habit of closely watching the exhaust is likely to prove serviceable in more ways than in keeping the engineer posted on the condition of the steam-distribution gear. Its sound often acts as a danger alarm, which should never go unheeded. Many an engine has gone home on one side, and not a few have been towed in cold, through accidents to the valve-gear, which could have been prevented had the engineer attended to the warning voice of a false exhaust. The nuts work off an eccentric-strap bolt; and it drops out, letting the strap open far enough to cause an uneven valve-travel. If the engineer hears this, and stops immediately to examine the machinery, he is likely to detect the defect before the strap breaks. Again, one side of a valve yoke may have snapped, leaving the other side to bear the load; or bolts belonging to different parts of the links or eccentric-straps may be working out,—so that the uniformity of the valve-travel is affected; and the same result may be produced by the eccentrics getting loose. Young engineers, to whom these pages are addressed, should make up their minds that an engine never exhausts an irregular note without something being the matter which does not admit of running to a station before being examined. It may only be an eccentric slipped a little way, a mishap that is not calculated to result disastrously; but, on the other hand, it is probably something of a more dangerous character.
NEGLECTING A WARNING.
Engineer Joy of the D. & E. road went in with a broken eccentric-strap. Questioning him about the accident brought out the fact, that, in starting from a station, he heard the engine make two or three curious exhausts; but he was running on a time-order, and did not wish to cause delay by stopping to examine the engine. But he had not gone half a mile when he found it necessary to stop and disconnect the engine, and by doing so held an express train forty minutes.
HOW AN ECCENTRIC-STRAP PUNCHED A HOLE IN A FIRE-BOX.
A representative case of neglecting a plain warning happened on an Illinois road some time ago. John Thomas was pulling a freight train up a grade, when, to use his own words, “The engine began to exhaust in the funniest way you ever heard. She would get on to three legs for an engine length or so, then she would work as square and true as she ever did, but only for a few turns, when she got to limping again.” This runner knew that something was wrong, and he determined to examine the engine at the next stopping-point. But delays in such a case are full of peril. When he got over the grade, and shut off steam, there was a tumultuous rattling of the reverse-lever, succeeded by a fearful pounding about the machinery; a tearing up of road-bed sent a shower of sand and gravel over the train; then a scream from escaping steam and water drowned all other noises, and the engine was enveloped in a cloud of blinding vapor. The forward bolt of one of the eccentric-strap rods had worked out, and allowed the end of the rod to drop on the track. Then it doubled up, and tore away the whole side of the motion; and part of a broken eccentric-strap knocked a hole in the fire-box. Here was the progress towards destruction. A small pin got lost, which permitted the nut of an important bolt to unscrew itself; then this bolt, with many a warning jar and jerk, escaped from its place in the link; and the conditions for a first-class break-down had come round.
INTEREST IN THE VALVE-MOTION AMONG ENGINEERS.
Whenever locomotive engineers congregate in the round-house, in the lodge or division room, a fruitful theme of conversation and discussion is the valve-motion. Curious opinions are often heard expressed upon this complex subject. There are comparatively few men who understand it properly: but it has a fascination which attracts all alike, the wise and the ignorant; and the man who is altogether uncertain about the true meaning of lap and lead, expansion and compression, is generally more loquacious on valve-motion than the engineer who has made the subject an industrious study.