Pressure differential bypass sensor switch with magnetic thermal lockout

A sensor switch for detecting fluid pressure differential across a filter in a fluid system, one side of said filter being exposed to a fluid in said fluid system which is at low pressure, the other side of said filter being exposed to said fluid in said fluid system which is at high pressure, said sensor switch comprising:

• housing means for locating said sensor switch in said fluid system;
• a reciprocable piston sealingly and slidably mounted in said housing means, said reciprocable piston being reciprocable between a first and a second stop position in said housing means, said reciprocable piston being exposed at one end to said fluid in said fluid system which is at low pressure, said reciprocable piston being exposed at its other end to said fluid in said fluid system which is at high pressure, said pressure differential across said filter in said fluid system thereby resulting in said piston being fluidically biased towards said second stop position;
• a spring located in said housing means biasing said reciprocable piston towards said first stop position, said reciprocable piston having a net biasing towards said first stop position when said fluid pressure differential in said fluid system is less than a first predetermined value, said reciprocable piston having a net biasing towards said second stop position when said fluid pressure differential in said fluid system exceeds said first predetermined value, said reciprocable piston being at said first stop position when said fluid differential pressure is less than said first predetermined value, said recpprocable piston being at said second stop position when said fluid differential pressure is equal to an allowable maximum fluid differential pressure across said filter in said fluid system;
• a permanent magnet attached to said reciprocable piston, said permanent magnet being reciprocable with said reciprocable piston;
• an electrical switch actuatable by a magnetic field, said electrical switch being attached to said housing means at a location in which said permanent magnet can only actuate said electrical switch when said reciprocable piston is substantially at said second stop position in said housing means;
• and
• a thermal ferrite material fixedly attached to said housing means adjacent said permanent magnet when said reciprocable piston is at said second stop position in said housing means, said thermal ferrite material having a predetermined Curie temperature, said thermal ferrite material preventing said electrical switch from being actuated when said thermal ferrite material is at a temperature below said Curie temperature.

A pressure differential sensor switch for use in a fluid circulating system, said pressure differential sensor switch performing an electrical switching function when an excessive pressure differential develops between a high fluid pressure location in said fluid circulating system and a low fluid pressure location in said fluid circulating system, said pressure differential switch comprising:

• a housing having a first passage with a central axis and a second passage with a central axis, said first passage having a first opening exposed to said high fluid pressure location, said first passage further having a second opening exposed to said low fluid pressure location, said central axis of said second passage being disposed in a non-parallel orientation with respect to said central axis of said first passage;
• a reciprocable piston sealingly and slidingly mounted in said first passage in said housing, said reciprocable piston being reciprocable between a first and a second stop position, said reciprocable piston having a first end that is exposed through said first opening to fluid pressure from said high fluid pressure location, said reciprocable piston having a second end exposed through said second opening to fluid pressure from said low pressure location, said reciprocable piston being thereby fluidically biased towards said second stop position, said reciprocable piston being at said first stop position when said fluid differential pressure is less than a first predetermined value, said reciprocable piston being at said second stop position when said fluid pressure differential reaches a second predetermined value;
• biasing means located in said housing for biasing said reciprocable piston toward said first stop position, said reciprocable piston having a net biasing toward said first stop position when said fluid pressure differential in said fluid circulating system is less than said first predetermined value, said reciprocable piston having a net biasing toward said second stop position when said fluid pressure differential in said fluid circulating system exceeds said first predetermined value;
• a permanent magnet attached to said reciprocable piston, said permanent magnet being reciprocable with said reciprocable piston;
• an axial travel electrical switch located in said second passage in said housing, said axial travel electrical switch having a magnetically susceptible switching element that is movable only along said central axis of said second passage, said magnetically susceptible switching element being movably responsive to magnetism of siid permanent magnet only when said reciprocable piston is substantially at said second stop position, said axial travel electrical switch being actuated when said magnetically susceptible switching element responds movably to said magnetism of said permanent magnet;
• and
• a thermal ferrite material fixedly attached to said housing adjacent said permanent magnet when said piston is at said second stop position, said thermal ferrite material having a predetermined Curie temperature, said thermal ferrite material preventing said axial travel electrical switch from being actuated when sadd thermal ferrite material is at a temperature below said Curie temperature.