A. When the pressure has been allowed to run down open the blow-off valve at the bottom of the boiler and let the water blow out less than a minute, till the water drops out of sight in the water gauges, or about two and one-half inches. Blowing
off more is only a waste of heat and fuel.
Q. What harm will be done by blowing off a boiler under a high pressure of steam?
A. The heat in the boiler while there is such a pressure will be so great that it will bake the scale on the inside of the boiler, and it will be very difficult to remove it afterward. After a boiler has been blown off the scale should be for the most part soft, so that it can be washed out by a hose and force pump.
Q. Why should a hot boiler never be filled with cold water?
A. Because the cold water will cause the boiler to contract more in some places than in others, and so suddenly that the whole will be badly strained. Leaky flues are made in this way, and the life of a boiler greatly shortened. As a rule a boiler should be filled only when the metal and the water put into it are about at the same temperature.
Q. After a boiler has been cleaned, how should the manhole and manhole plates be replaced?
A. They are held in position by a bolt passing through a yoke that straddles the hole; but to be steam and water tight they must have packing all around the junction of the plate with the boiler. The best packing is sheet rubber cut in the form of a ring just the right size for the bearing surface. Hemp or cotton packing are also used, but they should be free from all lumps and soaked in oil. Do not use any more than is absolutely needed. Be careful, also, to see that the bearings of the plate and boiler are clean and smooth, with all the old packing scraped off. Candle wick saturated with red lead is next best to rubber as packing.
Q. What are the chief duties of an engineer in care of a boiler?
A. First, to watch all gauges, fittings, and working parts, to see that they are in order; try the gauge cocks to make sure the water is at the right height; try the safety valve from time to time to be sure it is working; see that there are no leaks, that there is no rusting or wearing of parts, or to replace parts when they do begin to show wear; to examine the check valve frequently to make sure no water can escape through it from the boiler; take precautions against scale and stoppage of pipes by scale; and keep the fire going uniformly, cleanly, and in an economical fashion.