Diaphragm type differential pressure gauge with overpressure relief protection

Claim 1

In a differential pressure gauge that includes an annular housing member having a front end and a back end, a front cover secured to the housing member front end in hermetically sealed relation thereto, a back plate secured to the housing member back end, with said housing member and said back plate defining a pressure cavity, a flexible diaphragm clamped between said housing member back end and said back plate and disposed across said pressure cavity and separating same into a high pressure chamber on the front side of said diaphragm and a low pressure chamber on the back side of said diaphragm, and including linear to rotary motion transforming means including a helix journaled in said housing member for rotation about its longitudinal axis, with the helix having an indicator connected thereto disposed adjacent and visible through said front cover, a magnet mounted in said high pressure chamber for producing rotational movement of said helix about its said axis in response to linear movement of the magnet alongside and lengthwise of said helix axis, with said helix axis extending longitudinally of said housing member, means for connecting said diaphragm to said magnet whereby deflection of the diaphragm under differential pressures in said chambers produces said linear movement of said magnet, said diaphragm having a marginal edging thereabout comprising a continuous sealing bead, with said housing member back end and said back plate respectively defining annular clamping surfaces between which said diaphragm bead is clamped for hermetically sealing said chambers from each other about said diaphragm, which surfaces are coextensive with said bead, and means for separately connecting said high and low pressure chambers to sources of high and low pressure fluids, respectively, the improvement wherein: said means for connecting said high pressure chamber to the source of high pressure fluids comprises: a high pressure passage formed in said housing member and having its inlet end aligned with said diaphragm bead at said clamping surface of said housing member back end and its outlet end communicating with said high pressure chamber, a high pressure passage formed in said back cover plate and having its inlet end adapted for connection to the source of high pressure fluid and its outlet end aligned with said inlet end of said housing member high pressure passage and said diaphragm bead at said clamping surface of said back plate, said bead being apertured between and being in sealing relation about said housing member high pressure inlet end and said back plate high pressure passage outlet end for communicating said back plate high pressure passage to said housing member passage through said bead in hermetically sealed relation to said chambers, said housing member having formed in same a blowout passage extending longitudinally of said housing member and having its inlet end communicating with said high pressure chamber and its outlet end aligned with said diaphragm bead at said clamping surface of said housing member at a location spaced from said bead aperture along said diaphragm marginal edge, said back plate having formed in same a blowout passage aligned with said housing member blowout passage and having its inlet end aligned with said housing member blowout passage and said diaphragm bead at said clamping surface of said back plate and its outlet end directed rearwardly of said back plate, said bead being in sealing relation about said housing member blowout passage outlet end and said back plate blowout passage inlet end and defining therebetween an impervious flangible membrane, said housing member and back plate high pressure passages and said diaphragm aperture communicating therebetween being similar in effective orifice area, said housing member and back plate blowout passages each having an effective orifice area that is a predetermined multiple of said effective orifice area of said housing member and back plate high pressure passages and said aperture therefor, said effective orifice area of said housing member and back plate high pressure passages and said aperture therefor being of rounded opening configuration aligned with said diaphragm bead, said effective orifice area of said housing member and back plate blowout passages being of elongate opening configuration that extends longitudinally of said bead for orienting same to have said predetermined area multiple as compared to said effective orifice area of said housing member and back plate passages within the confines of the hermetic sealing defined by said bead and said clamping surfaces.