Importance

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Abstract

A temperature compensating differential pressure indicating device having a lock-out feature requiring internal reset after actuation. The differential pressure responsive indicating device includes a case having an internal chamber and a piston reciprocably and sealingly disposed in the internal chamber. A piston follower is also reciprocably disposed in the internal chamber and abuts against the piston. A first biasing element biases the piston and the piston follower in a first direction while a second biasing element biases these components in the opposite direction, the second biasing element being weaker than the first biasing element. The piston is displaceable in response to the pressure differential between an inlet pressure and an outlet pressure. A shape memory alloy temperature responsive abutment permits the piston follower to move together with the piston at or above a predetermined temperature, while preventing motion of the piston follower below the predetermined temperature. An indicator is provided which indicates, by displacement, the displacement of the piston follower beyond a predetermined axial position, thus indicating that the predetermined pressure differential and the predetermined temperature have been simultaneously exceeded.

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First Claim