Pressure differential indicator with non-mechanical thermal lockout

An indicator for indicating a predetermined value of fluid pressure differential of a fluid in a fluid system, comprising:

• body means for locating said indicator in said fluid system;
• a reciprocable piston sealingly mounted in said body means, said reciprocable piston being exposed to said fluid pressure differential in said fluid system, said piston being thereby fluidically biased in a first direction;
• first biasing means located in said body means for biasing said reciprocable piston in a direction opposite said first direction;
• an indicator button reciprocably, mounted to said body means, said button having attached thereto a first magnetic material element;
• second biasing means located in said body means for biasing said indicator button in a direction opposite said first direction;
• a second magnetic material element attached to said reciprocable piston, said first magnetic material element being magnetically attractive with said second magnetic material element, said reciprocable piston being thereby magnetically biased in a direction opposite said first direction and said indicator button being thereby magnetically biased in said first direction;
• and
• a thermal ferrite element having a predetermined Curie temperature attached to said body means, said thermal ferrite element increasing said magnetic attraction when said thermal ferrite element is substantially at a temperature below said Curie temperature, said indicator button being magnetically biased by said first and second magnetic materials in said first direction when said fluid pressure differential is less than said predetermined value, said indicator button being magnetically biased by said thermal ferrite element in said first direction when said fluid pressure differential exceeds said predetermined value and said thermal ferrite element is substantially at a temperature below said predetermined Curie temperature, said indicator button being moved by said second biasing means in a direction opposite said first direction when said fluid pressure differential exceeds said predetermined value and said thermal ferrite element is substantially at a temperature above said predetermined Curie temperature.

An indicator for use in a fluid system for indicating an excessive differential in pressure of a fluid in said fluid system between a high pressure location in said fluid system and a low pressure location in said fluid system, said indicator comprising:

• a reciprocable piston having a first end exposed to said fluid at said high pressure location in said fluid system and a second end exposed to said fluid at said low pressure location in said fluid system;
• a spring resiliently biasing said piston toward said high pressure location in said fluid system, said spring biasing said piston will maintain said piston at said high pressure location in said fluid system when the difference in pressure between said high pressure location in said fluid system and said low pressure location in said fluid system is below a predetermined pressure differential, said spring biasing said piston further will not maintain said piston at said high pressure location in said fluid system when said difference in pressure exceeds said predetermined pressure differential, whereby said piston will move toward said low pressure location in said fluid system when said difference in pressure exceeds said predermined pressure differential;
• permanent magnet means carried by said reciprocable piston;
• indicator button means having a magnetically permeable element carried thereby, said indicator button means being reciprocable between a first position in which said magnetically permeable element is adjacent said permanent magnet means and a second position in which said magnetically permeable element is spaced apart from said permanent magnet means, said permanent magnet means imposing a first magnetic force on said magnetically permeable element that attracts said indicator button means toward said first position;
• a second spring resiliently biasing said indicator button means toward said second position, said second spring biasing on said indicator button means imposing a biasing force which is less than said magnetic force when said reciprocable piston is at said high pressure location in said fluid system and being greater than said first magnetic force when said reciprocable piston is at said low pressure location in said fluid system, whereby said second spring will move said indicator button means from said first position to said second position when said reciprocable piston moves from said high pressure location in said fluid system to said low pressure location in said fluid system;
• and
• a thermal ferrite element that is magnetic at temperatures below a narrow, predetermined temperature range and that is substantially less magnetic at temperatures above said narrow predetermined temperature range, said thermal ferrite element being positioned relative to said permanent magnet means so as to impose a second magnetic force on said indicator button means when said thermal ferrite element is at a temperature below said narrow, predetermined temperature range, said second magnetic force causing said indicator button means to remain at said first position even when said reciprocable piston moves to said low pressure location in said fluid system, said second magnetic force imposed by said thermal ferrite element on said indicator button means when said thermal ferrite element is at a temperature above said narrow, predetermined temperature range thereby permitting said second spring to move said indicator button means from said first position to said second position when said reciprocable piston moves to said low pressure location in said fluid system.