Fluid flow control valve

A fluid flow control valve comprising a valve body having an inlet and an outlet, a valve seat, a valve closure member co-operating with said seat for closing off the inlet from the outlet, said valve closure member being between said valve seat and said inlet and being biased into sealing contact with said seat, an aperture in said body, said aperture being bounded by a peripheral wall, and a valve-operating member of synthetic plastics material projecting from said body through said aperture, said operating member comprising a relatively stiff, disc-like flexible diaphragm and a stem integral with the diaphragm, positioned centrally thereof and projecting in both directions therefrom, an annular peripheral part of said diaphragm, and an annular inner part of said diaphragm adjacent to and encircling said stem, being thicker than a circumferentially extending region which lies between said peripheral part and said inner part, said diaphragm engaging said peripheral wall whereby the diaphragm seals said aperture, said region of the diaphragm, said stem and said inner part of the diaphragm being spaced from said body, and said stem and inner part being displaceable with respect to said peripheral part, said stem being attached, on one side of the diaphragm, to said valve closure member and on the other side of the diaphragm constituting an operating element the outer end of which can be displaced generally parallel to the plane of the diaphragm so as to pivot about a point located substantially in the medial plane between the faces of the diaphragm and displace said closure member with respect to the seat, the resultant distortion of the inner part of the diaphragm with respect to said peripheral part at said region creating a restoring force.