Normally open pressure responsive switch

A normally open pressure responsive electrical switch comprising

• a first electrically insulative base member having a top and bottom surface formed with a recess in the top surface,
• a first electrically conductive terminal extending from outside the base member into the recess and mounting an electrical contact thereon in the recess,
• a second electrically conductive terminal received on the top surface of the base member electrically isolated from the first electrically conductive terminal, the second electrically conductive terminal formed with a disc receiving seat thereon,
• an electrically conductive disc movable between opposite convex, concave dished configurations disposed on the disc receiving seat in alignment with the electrical contact and at its first at rest configuration being out of engagement with the electrical contact,
• a second electrically insulative base member received over the second electrically conductive terminal and being attached to the first base member, the second base member having top and bottom surfaces and having an opening extending therebetween,
• a piston element movably received within the opening in engagement with the disc,
• a thin flexible diaphragm received on the second base member closing the opening;
• and
• O-ring seal means received over the thin flexible diaphragm, a wall member extending upwardly from the top surface of the second base member spaced from and around the periphery of the opening, the O-ring seal means comprising an annular flexible member having a generally a flat bottom surface and an outer surface extending upwardly from the bottom surface, the outer surface having first and second outer surface portions, the first outer surface portion being generally cylindrical extending upwardly from the bottom surface and the second outer surface portion being a frusto-conical surface, the height of the wall member being such that a plane passing through the top of the wall member would intersect the second outer surface portion, when exposed to a pressure medium above a selected level the diaphragm will deflect forcing the piston to move against the disc until the disc moves to its second actuated configuration in engagement with the electrical contact.