The most common causes of trouble with the throttle are the breaking or working out of one of the bolts that operate the valve within the dome, the breaking of a valve-rod, or working off of nuts that should secure the connection. Where the throttle fails with the valve closed, and the engineer finds it necessary to take the dome-cover off to prevent his engine from being hauled in, he will generally find the trouble to lie with the connections mentioned, or with the bolts belonging to the bell-crank, that is located near the bottom of the stand-pipe. Sometimes the nuts on the top of the throttle-valve stem work off: but, in such a case, there is no difficulty in opening the valve; it is when the engineer wants to close it, that the discomfiture comes in. Some steam-pipes are provided with a release-valve near the throttle, to relieve the pipe from intense back-pressure when the engine is reversed. The sudden reversing of an engine sometimes jerks this valve out of its seat, leaving an open passage between the boiler and steam-chest. This acts like a mild case of unshipped throttle, and must be controlled in a similar way.
BURSTING A DRY PIPE.
The bursting of a dry pipe is similar in effect to the action of a throttle becoming disconnected while open; and it may even prove harder to control, according to the size of the opening. Engineer Halliday had a trying time with a case of this kind. While swinging along the E., F., & G. road, with a heavy train of freight, a herd of horses ran in from an open crossing-gate, and started up the track just in front of the engine. As there was a bridge a short distance ahead, Halliday reversed the engine in his anxiety to prevent an accident. The train stopped for an instant, when the engine began to push it back. Halliday tried to throw the lever to the center, but never before had he felt such a pressure acting upon it. Again and again he tried to throw the lever over; but every time it proved too formidable a struggle, and the catch found its way into the full-back notch. Meanwhile, the train was gaining speed in the wrong direction, and a passenger train was not many miles behind. Beginning to realize the true state of affairs, Halliday called for brakes, opened the fire-box door, closed the dampers, and started the injector. Then he directed the fireman to throw some bucketfuls of water upon the fire, while he tied down the whistle-lever, letting the steam blow. The promptest means for reducing the pressure of steam were now in operation, and his next move was to try the reverse-lever again. Both men grasped the lever, and, by a combined effort, forced it past the center; and Samson’s hair was cut. It was afterwards found that a long rent had opened in the dry pipe, letting the full boiler pressure upon the valves, which moved hard through being dry; the hot gases pumped through them in reverse motion having licked off every trace of lubricating unguent.
OTHER THROTTLE ACCIDENTS.
Cases of serious trouble resulting from accidents to throttle connections would be easy to multiply. Two incidents with similar originating conditions, but with very different results, will suffice. Engineer Phelps was pulling a full train of coal over rails that were neither wet nor dry, and had just enough frost upon them to be wicked. He was having a bad time slipping, but was working patiently along, when the throttle became disconnected with the valve open. The engine at once started on a whirl of slipping that threatened disaster, but it was immediately controlled by the engineer pulling the reverse-lever to the center notch. Engineer Cook of the F., G., & H. road, was not so fortunate when the stem of his throttle-valve broke on a slippery day. As the wheels began spinning round, Cook lost his head, and kept working at the throttle-lever to try to stop. Seeing this was of no avail, he grasped the sand-lever, and tugged vigorously at the valves. A season of tumult succeeded; and, when the engine stopped presently, it was found to be a deplorable wreck. It was hard to tell, from the look of the ruin, what part of the locomotive broke first; but the crank-pins on one side were cleaned off, and the piston was out through the cylinder-head. The side-rod on the other side broke close to the strap, and was twisted up like a spiral spring.
POUNDING OF THE WORKING-PARTS.
It is good for an ambitious young engineer, who desires to thoroughly master his calling, to walk occasionally into the room where a well-managed automatic cut-off engine is at work, and watch its smooth, noise-less movements. There he may find an ideal of how an engine should run. The nature of the work performed by a locomotive engine prevents it from being operated noiselessly, and the smoothness of its action must always compare unfavorably with a well-constructed stationary engine; but the connections which transmit the power of a locomotive should be free from knock or jar, if they are properly proportioned, and skillfully put together.
SOME CAUSES OF POUNDING.
To an engineer with a well-regulated mind, a pound about the engine is a source of continual irritation. If a pound arises from a cause which can be remedied by an engineer, the careful man will soon perform the necessary work to end the noise. Sometimes the origin of a pound is hard to discover: very often it is beyond the power of the engineer to stop it. Some makes of locomotives always pound when working in full gear. With such an engine, a nervous engineer will fuss, pushing up wedges until they stick fast, and cause no end of grief to get them down again. He will key up the main-rod connections till they run hot, and he will prophesy that the engine is going to pieces. But the engine hangs together all the same, and is only suffering from want of lead, or want of compression. Where an engine is deficient in the cushioning to the piston, due to compression or lead, the momentum of the piston and connecting-rod is suddenly checked at the end of each stroke. The concussion to these working-parts is so great that pounding will be produced. As the engine gets hooked towards the center, this pounding will cease, because the lead opening increases as the motion is notched back. The most common causes for pounding with locomotives are worn main-rod connections, and driving-boxes too loose in the jaws, or the brasses loose in the driving-boxes. If side-rods are out of tram, or have the brasses badly worn, they sometimes pound when passing the centers. A cross-head will pound when the guides are worn very open. This last defect is liable to cause a bent piston-rod. A piston makes a tremendous pound when a badly connected rod allows it to touch a cylinder-head, and a very ominous pound is produced when the spider gets loose on the piston-rod, and a piston-rod loose in the cross-head will make itself heard all over the engine.