OVER-PRESSURE.
Should it happen from any cause that the safety-valves fail to relieve the boiler, and the steam runs up beyond a safe tension, the situation is critical; but the engineer should not resort to any method of giving sudden relief. To jerk the safety-valve wide open at such a time is a most dangerous proceeding. A disastrous explosion lately occurred to a locomotive boiler from this cause. The safety-valves had been working badly; and, while the engine was standing on a side track, they allowed the steam to rise considerably above the working-pressure. When the engineer perceived this, he threw open the safety-valve by means of a relief lever, and the boiler instantly went into fragments. Cases have occurred where the quick opening of a throttle-valve has produced a similar result. The proximate cause of such an accident was the violent motion of water and steam within the boiler, induced by the sudden diminution of pressure at one point; but the real cause of the disaster was a weak boiler,—a boiler with insufficient margin of resisting power. The weakest part of a boiler is its strongest point. This may seem paradoxical, but a moment’s reflection will show that the highest strength of a boiler merely reaches to the point where it will give out. Hence engineers should see that a boiler is properly examined for unseen defects so soon as signs of distress appear. Leaky throat-sheets or seams, stay-heads dripping, or incipient cracks, are indications of weakness; and their call should be attended to without delay.
RELIEVING OVER-PRESSURE.
When an engineer finds the steam rising beyond a safe pressure, he should reduce it by opening the heaters, starting the injector, dampening the fire, or even by blowing the whistle. The whistle offers a convenient means of getting rid of superfluous steam, and its noise can be stopped by tying a rag between the bell and the valve opening.
BURSTED FLUES.
Should any boiler attachment, such as a check-valve or blow-off cock, blow out or break off, no time should be lost in quenching the fire. That is the first consideration. A bursted flue will generally save an engineer the labor of extinguishing the fire. In this case an engineer’s efforts should be directed to reducing the pressure of steam as quickly as possible, so that he may be able to plug the flue before the water gets out of the boiler. Flue-plugs and a rod for holding them are very requisite articles; but, in driving flue-plugs, care must be exercised not to hammer too hard, or a broken flue-sheet may result. Plugs are often at hand without a rod to hold them. In such an emergency, a hard wooden rail can be used; the plug being fastened to the end by means of nails and wire, or even wet cord. Where no iron plug is available, a wooden plug driven well in, away from the reach of the fire, may prevent a bursted flue from leaking, and enable the engine to go along; but wooden plugs are very unreliable for such a purpose. They may hold if the rupture in the flue should be some distance inside; but, should the cause of leaking be close to the flue-sheet, a wooden plug will burn out in a few minutes.