Pressure differential bypass sensor switch with magnetic thermal lockout

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. This movement of the reciprocable piston will carry the permanent magnet to a position relative to the magnetically actuatable electrical switch in which the magnetic field thereof will cause the magnetically actuatable electrical switch to actuate, thereby providing a warning signal indicating an impending filter bypass operating condition. A thermal ferrite is provided adjacent the permanent magnet. The thermal ferrite is selected to have a Curie temperature corresponding to the temperature below which fluid viscosity in the fluid system is high. In the event the reciprocable piston moves due to a pressure differential attributable to high fluid viscosity because of operation below the Curie temperature, the thermal ferrite will act to regionally confine the magnetic field of the permanent magnet, resulting in no actuation of the magnetically actuatable electrical switch.