Rotary valve

A rotary control valve comprising

• a valve housing having a longitudinal axis, a fluid inlet, and a fluid outlet,
• an axle in said housing having an axis which is at right angles to and is laterally displaced from said housing axis,
• a plug mounted on said axle for rotation therewith within said housing, said plug having a spherical sealing surface which is rotated about said axis of said axle upon the rotation of said axle,
• a flexible seat ring located in said housing between said inlet and said outlet, said seat ring having an annular outer portion having an axis coinciding with said housing axis and having an annular intermediate diaphragm portion of cup-shaped cross-section which extends from said outer portion substantially in the direction of the said axis of said outer portion and turns through substantially a right angle to terminate in two oppositely-directed annular lips which extend substantially at right angles to said diaphragm portion and parallel to said axis of said outer portion, and
• an annular retaining ring having an annular outer collar portion and having an annular inner collar portion constituting a hard seat portion, said outer collar portion being secured in said housing concentrically with said housing axis to secure therein said outer portion of said seat ring with one of said annular lips facing said axle, and with the other of said annular lips facing said hard seat portion,
• whereby rotation of said plug which brings said spherical sealing surface into contact with said one of said annular lips establishes sealing engagement between the latter and said spherical sealing surface, and brings said other of said annular lips into sealing engagement with said hard seat portion, thereby to seal said inlet from said outlet.