Abstract: A bidirectional fluid flow control valve has two bifurcated elastic seat rings positioned in respective undercut grooves which are spaced apart in the flow passageway of the valve body, one on either side of the axis of rotation of a butterfly valve disc having two corresponding spaced apart annular sealing surfaces. One of the undercut seat grooves may be formed in a separate detachable seal ring to facilitate assembly of the disc in the valve. The valve disc is axially symmetrical with respect to its midplane, so that operating torque and flow characteristics of the valve are the same regardless of the direction of fluid flow through the valve.

Abstract: A valve seal mechanism for cryogenic applications includes an undercut groove in a seating region of the fluid passageway in a valve body. Disposed within the groove is a shouldered resilient wear ring of polytetrafluoroethylene, the outer circumference of the shouldered portion of the wear ring having a V-shaped channel formed therein. A solid backing ring having an inner circumferential surface of wedge-shaped cross section makes an interference fit with the V-channel of the wear ring, thereby preloading the channel sides against the respective adjacent sides of the groove. A valve disc has a sealing surface which makes an interference fit with a seating surface forming the inner circumferential surface of the wear ring. Introduction of fluid under pressure and reduction of temperatures from normal ambient to cryogenic both tend to increase sealing effectiveness.

Abstract: A power-driven quarter-turn valve actuator includes a reciprocating drive member in the form of a rod mounted perpendicularly to and spaced a preselected distance from a valve stem. A crank arm is coupled to the valve stem so that the axis of the crank arm makes an angle of between approximately 60.degree. and 100.degree. with a line intersecting the stem axis and perpendicular to the rod axis when the valve is shut and makes an angle of between minus 30.degree. and plus 10.degree. with said line when the valve is fully open. A link member connects the outer end of the crank arm to a point on the reciprocating rod. The preselected distance between actuator rod and valve stem, and the lengths of the crank arm and link, are chosen to produce a variable actuator torque output curve that closely matches the operating torque requirements of the valve.