Composite diaphragm for hydraulic pressure failure alarm switch - involving components of PTFE, nitrile rubber and or polyurethane rubber

摘要

Diaphragm for use in an electrical contact switch actuated by hydraulic pressure comprises a stack of discs assembled so that the face in contact with the hydraulic oil is made of nitrile rubber (sulphur-cured), the face in contact with a spring loaded plunger is made of polyurethane rubber, and a thin (0.1-0.2 mm.) disc of PTFE is interposed between the two rubber discs, to act effectively as a solid interfacial lubricant. Pref. the seat which retains the polyurethane rubber is faced with an annular cover of PTFE, to inhibit extrusion of the polyurethane disc into the adjacent switch piston chamber by sustained pressure. Arrangement is esp. suitable for switches operating at pressures up to 200 bar and 80 degrees C., to activate an alarm if the pressure drops below a min. value e.g. is approx. 70 bars.