Maxims and Instructions for the Boiler Room / Useful to Engineers, Firemen & Mechanics; Relating to Steam Generators, Pumps, Appliances, Steam Heating, Practical Plumbing, etc.

by N. Hawkins

Fig. 89.

A small drain cock should be fitted to the leg of the syphon of a steam gauge, leading to the boiler, at a level with the highest point the water can rise in the other leg, otherwise an increased pressure will be indicated, due to the head of water which would otherwise collect in the boiler leg of the syphon.

Steam gauges indicate the pressure of steam above the atmosphere only, the total pressure being measured from a perfect vacuum which will add 14⁷⁄₁₀ lbs. on the average to the pressure shown on the steam gauge.

These gauges are apt to get out of order in consequence of water lodging in the end of the heat tube and corroding the latter. It may be easily known when they are out of order by raising the pressure of the steam in the boiler and watching when it commences to blow off at the safety valve, and then noting the position of the index finger. The pressure registered by the finger should, of course, then correspond with the known blow off pressure of the valves; if it does not, one or the other or both of these instruments must be out of order; therefore, when this is the case and a disagreement occurs, the steam gauge may be presumed to need correction.

It should also be noted that the steam gauge finger points to zero when steam pressure is cut off. A two-way cock should be used for closing the connection between the steam gauge and the boiler, and at the same time to let air into the steam gauge.

The steam should never be allowed to act directly on a steam gauge when located in cold situations where they are liable to freeze. The valve on the boiler should be closed and the water allowed to drip out, and, before the steam is turned on from the boiler, the drip on the gauge should be closed, in order that sufficient steam may be condensed in the pipe to furnish the quantity of water necessary to keep the steam from striking the gauge.

A ready method for being always able to prove the correctness of your steam gauge.

When steam is at some point not over half the usual pressure, place the ball on the safety valve at the point where it commences to blow off and mark the place. Move the ball twice as far from the fulcrum as this mark, and it should blow off at twice the pressure as indicated by the gauge, or it is not right. Any other relative distance may be used to advantage.