Patent ID: 8403296

Claim:
A gate valve, comprising: a housing having flow passages with a common flow passage axis intersected by a gate cavity, each of the flow passages having a counterbore formed at an intersection of the gate cavity with each of the flow passages, each of the counterbores having a cylindrical inner wall and a rear wall; a gate that is movable within the cavity perpendicular to the flow passage axis for opening and closing the flow passages; a seat ring carried in each of the counterbores, each of the seat rings being axially movable relative to the counterbores between a forward position and a rearward position and comprising: a forward end for engagement by the gate, which pushes the seat rings from the forward position to the rearward position when the gate is moved into engagement with the seat rings; a rearward end that is spaced forward of the rear wall of the counterbore while the seat ring is in the forward position and into abutment with the rein wall while the seat ring is in the rearward position; a passage having a longitudinal axis and extending from forward end through the seat ring to the rearward end; a flexible lip formed on the seat ring at the rearward end, the flexible lip having a rearward sealing surface formed thereon that elastically deflects into sealing engagement with the rear wall of the counterbore when the gate moves the seat ring to the rearward position; and the flexible lip further having an outward sealing surface formed thereon that elastically deflects into sealing engagement with the cylindrical inner wall of the counterbore when the gate moves the seat ring to the rearward position.