Rough and Tumble Engineering

by James H. Maggard

As this is the duty of the steam gauge, it is necessary that it be absolutely correct. By the use of an unreliable gauge you may become thoroughly bewildered, and in reality know nothing of what pressure you are carrying.

This will occur in about this way: Your steam gauge becomes weak, and if your safety is set at I00 pounds, it will show I00 or even more before the pop allows the steam to escape; or if the gauge becomes clogged, the pop may blow off when the gauge only shows go pounds or less. This latter is really more dangerous than the former. As you would most naturally conclude that your safety was getting weak, and about the first thing you would do would be to screw it down so that the gauge would show I00 before the pop would blow off, when in fact you would have I00 or more.

So you can see at once how important it is that your gauge and safety should work exactly together, and there is but one way to make certain of this, and that is to test your steam gauge. If you know the steam gauge is correct, you can make your safety valve agree with it; but never try to make it do it till you know the gauge is reliable.

HOW TO TEST A STEAM GAUGE

Take it off, and take it to some shop where there is a steam boiler in active use; have the engineer attach your gauge where it will receive the direct pressure, and if it shows the same as his gauge, it is reasonable to suppose that your gauge is correct. If the engineer to whom you take your gauge should say he thinks his gauge is weak, or a little strong, then go somewhere else. I have already told you that I did not want you to think anything about your engine-I want you to know it. However, should you find that your gauge shows when tested with another gauge, that it is weak, or unreliable in any way, you want to repair it at once, and the safest way is to get a new one; and yet I would advise you first to examine it and see if you cannot discover the trouble. It frequently happens that the pointer becomes loosened on the journal or spindle, which attaches it to the mechanism that operates it. If this is the trouble, it is easily remedied, but should the trouble prove to be in the spring, or the delicate mechanism, it would be much more satisfactory to get a new one.

In selecting a new gauge you will be better satisfied with a gauge having a double spring or tube, as they are less liable to freeze or become strained from a high pressure, and the double spring will not allow the needle or pointer to vibrate when subject to a shock or sudden increase of pressure, as with the single spring. A careful engineer will have nothing to do with a defective steam gauge or an unreliable safety valve. Some steam gauges are provided with a seal, and as long as this seal is not broken the factory will make it good.

FUSIBLE PLUG

We have told you about a safety valve, we will now have something to say of a safety plug. A safety, or fusible plug, is a hollow brass plug or bolt, screwed into the top crown sheet. The hole through the plug being filled with some soft metal that will fuse at a much less temperature than is required to burn iron. The heat from the firebox will have no effect on this fusible plug as long as the crown sheet is covered with water, but the moment that the water level falls below the top of the crown sheet, thereby exposing the plug, this soft metal is melted and runs out, allows the steam to rush down through the opening in the lug, putting out the fire and preventing any injury to the boiler. This all sounds very nice, but I am free to confess that I am not an advocate of a fusible plug. After telling you to never allow the water to get low, and then to say there is something to even make this allowable, sounds very much like the preacher who told his boy "never to go fishing on Sunday, but if he did go, to be sure and bring home the fish." I would have no objection to the safety plug if the engineer did not know it was there. I am aware that some states require that all engines be fitted with a fusible plug. I do not question their good intentions, but I do question their good judgment. It seems to me the are granting a license to carelessness. For instance, an engineer is running with a low gauge of water, owing possibly to the tank being delayed longer than usual, he knows the water is getting low, but he says to himself, "well, if the water gets too low I will only blow out the plug," and so he continues to run until the tank arrives. If the plug holds, he at once begins to pump in cold water, and most likely does it on a very hot sheet, which of itself, is something he never should do; and if the plug does blow out he is delayed a couple of hours, at least, before he can put in a new plug and get up steam again. Now suppose he had not had a soft plug (as they are sometimes called). He would have stopped before he had low water. He would not even have had a hot crown sheet, and would only have lost the time he waited on the tank. This is not a fancied circumstance by any means, for it happens every day. The engineer running an engine with a safety plug seldom stops for a load of water until he blows out the plug. It frequently happens that a fusible plug becomes corroded to such an extent that it will stand a heat sufficient to burn the iron. This is my greatest objection to it. The engineer continues to rely on it for safety, the same as if it were in perfect order, and the ultimate result is he burns or cracks his crown sheet. I have already stated that I have no objection to the plug, if the engineer did not know it was there, so if you must use one, attend to it, and every time you clean your boiler scrape the upper or water end of the plug with a knife, and be careful to remove any corrosive matter that may have collected on it, and then treat your boiler exactly as though there was no such a thing as a safety plug in it. A safety plug was not designed to let you run with any lower gauge of water. It is placed there to prevent injury to the boiler, in case of an accident or when, by some means, you might be deceived in your gauge of water, or if by mistake, a fire was started without any water in the boiler.

Should the plug melt out, it is necessary to replace it at once, or as soon as the heat will permit you to do so. It might be a saving of time to have an extra plug always ready, then all you have to do is to remove the melted one by unscrewing it from the crown sheet and screwing the extra one in. But if you have no extra plug you must remove the first one and refill it with babbitt. You can do this by filling one end of the plug with wet clay and pouring the metal into the other end, and then pounding it down smooth to prevent any leaking. This done, you can screw the plug back into its place.

If you should have two plugs, as soon as you have melted out one replace it with the new one, and refill the other at your earliest convenience. By the time you have replaced a fusible plug a few times in a hot boiler you will conclude it is better to keep water over your crown sheet.