When the floats of wet gas-meters are being soldered together, the air inside the floats becomes rarefied owing to the increased temperature caused by the heat of the bolt used in soldering. When this inside air is cooled by the water in the meter, the pressure of the outside air upon the float becomes so great that any sudden slight increase of pressure will frequently overcome the resistance of the metal, which is only soft pewter. Floats should always be made with egg-shaped ends instead of flat ends, so as to offer more resistance. In dry gas-meters the faces of the hard white metal valves sometimes become coated with a deposit, caused probably by the action of the gas on the oil used to keep the diaphragms soft. In course of time this deposit hardens until the pressure of the gas is insufficient to move the valve cover. The top of the meter and the top of the valve-box inside should be taken off, and the valve covers taken out and thoroughly cleaned with a little naphtha, the faces of the valves being treated in the same manner; the meter should then be put together again and be re-tested and stamped by an authorised inspector.

The only remedy is to soften the diaphragms with an oil that is not affected by the particular gas in use.