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The pressure in the boiler is shown by a steam gauge, pressure gauge, or dial gauge as it is promiscuously called.

A Bourdon dial gauge or pressure gauge consists of a dial casing, containing a hollow thin brass hoop, oval in cross section, which receives steam from the boiler.

All the passage ways connecting to dial gauge, R, with the fluid chamber above piston, E, are filled solid with fluid, permitting no air spaces that can be avoided.

The steel plug, L, that forms a passage way between the fluid chamber and the dial gauge, is provided on one side with a small screw hydraulic pump, with a reservoir supply of fluid.