Sealed casing for pressure gauge

摘要

An improved solid front casing for a pressure gauge that is readily field converted from a dust-tight to either a hermetically sealed air-tight or hermetically sealed liquid-tight construction. A flexible closure element is axially supported over a rear opening in the case by a threaded connection with threads formed in the case peripherally surrounding the opening. For either hermetically sealed air-tight or liquid-tight service a self-threaded closure element is replaced by a flexible diaphragm of controlled spring rate axially clamped by a threaded backup ring. Temperature induced volumetric changes imposed on the liquid fill or air fill are compensated for by the spring rate of the diaphragm. In the event of an overpressure occurring internally of the casing the diaphragm can escape from its clamping relation for affording pressure relief. An annular groove formed peripherally about the Bourdon tube socket where extending through the stem aperture of the casing cooperates with the surrounding casing wall to receive an externally applied O-ring for field forming a liquid-tight joint thereat.