Differential pressure indicator

Claim 1

In a differential pressure indicator for a fluid system including a moveable piston, said piston including a magnetically attractable substance, said piston and said magnetically attractable substance enclosed in said differential pressure indicator, a high pressure fluid inlet from the outside of said differential pressure indicator opening to one side of saId piston, a low pressure fluid inlet between the outside of said differential pressure indicator opening into another side of said piston, sealing means between said piston and said differential high pressure and low pressure openings, said sealing means to inhibit the flow of fluid past said high pressure and low pressure side of said piston, a magnet in said differential pressure indicator having a surface outside the differential pressure indicator area of high pressure and low pressure fluid intake, a button including a magnetically attractable substance, said button adjacent said magnet''s surface outside the differential pressure indicator''s area of high pressure and low pressure fluid intake, means normally biasing said button away from said magnet, said button''s magnetically attractable substance normally held to said magnet, said magnet including a longitudinal portion of lesser size than the inside of said differential pressure indicator''s area of high pressure and low pressure fluid intake, said piston shaped to overlap said magnet''s longitudinal position when said piston is urged by said fluid differential pressure towards said magnet, said piston then drawing off magnetic flux releasing said button from said magnet decreasing the magnetic flux to release the button against its biasing.