Abstract: A pressure differential bypass sensor switch with thermal lockout that utilizes change in position of a permanent magnet carried by a reciprocable piston responsive to pressure differential in a fluid system to actuate a magnetically actuatable electrical switch. Opposite sides of the reciprocable piston are exposed, respectively, to high pressure and low pressure sides of a filter located in a fluid circulating system. The reciprocable piston is normally positioned at the high pressure side of a passage in which it reciprocates, due to biasing by a spring acting on it from the low pressure side of the passage. As the filter becomes clogged, the pressure differential across it and, therefore, across the reciprocable piston will increase. The bypass sensor is calibrated so that a maximum allowable pressure differential in the fluid system will drive the reciprocable piston to the low pressure side of the passage.

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.

Abstract: An excessive pressure differential indicating device for use with a filter in a liquid circulating system. The device has a reciprocable piston that reciprocates between a high pressure location, when the pressure differential is not excessive, and a low pressure location, when the pressure differential is excessive. The device has an indicator button with a magnetically conductive element, and the button is retained in a non-indicating position when the reciprocable piston is at the high pressure location by magnetic attraction between a permanent magnet carried by the reciprocable piston and the magnetically conductive element, a spring being provided to bias the indicator button to an indicating position when the reciprocable piston moves with the permanent magnet away from the indicator button to the low pressure location.

Abstract: A pressure differential bypass sensor switch that utilizes the change in piston of a permanent magnet that is carried by a reciprocable position to actuate the switching element of an axial travel switch by the change in magnetic forces that act on the switching element as a result of the change in position of the reciprocable piston and the permanent magnet. Opposite sides of the piston are exposed, respectively, to the high pressure and low pressure sides of a filter in a liquid circulating system, and the piston is normally positioned at the high pressure side of a passage in which it travels by a spring that acts on it from the low pressure side. As the filter becomes clogged the pressure drop across it and, therefore, across the piston will increase, and the piston is calibrated so that an excessive pressure drop will drive it to the low pressure side.