Gate valve

Claim 1

In a gate valve comprising: a valve body having a valve chamber therein and a pair of flow passages extending therethrough at opposite sides of said valve chamber; and, a gate member within said valve chamber and reciprocably movable along a line transverse to said valve body flow passages between a gate position in which said valve is closed and a gate position in which said valve is open, said gate member having a flow passage therethrough which is aligned with the valve body flow passages when said gate member is in said open position and an imperforate portion which is aligned with said valve body flow passages when said gate member is in said closed position, said gate member being adapted to seal the downstream valve body flow passage by fluid pressure against the gate member on the upstream side thereof from the upstream valve body flow passage, the valve body and gate means being constructed such that fluid from the upstream valve body flow passage passes into the valve body during movement of the gate member between the open position and closed position; the improvement comprising seal means for preventing flow of fluid from said upstream valve body flow passage along the surface of the gate member imperforate section, said seal means including a primary seal means and a secondary seal means; said primary seal means comprising a recess around the inner end of at least said upstream flow passage adjacent the gate member, a primary seal seat member slidably mounted in said recess and surrounding the upstream flow passage adjacent to said gate member, said primary seal seat member having a first surface and a second surface, primary seal spring means normally biasing said primary seal seat member toward the gate member such that when the gate member is in said closed position an initial primary seal is provided by said primary seal seat member against said gate member at said first surface; said first surface and said second surface each being exposed to the pressure of fluid in said upstream flow passage, said second surface having an area exposed to such fluid pressure greater than the area of said first surface exposed to such fluid pressure whereby the fluid pressure in said upstream flow passage forces the primary seal seat member against the gate member and establishes a primary seal preventing flow along the surface of said gate member when it is in said closed position; said secondary seal means comprising a secondary seal seat member slidably mounted on and closely surrounding said primary seal seat member, said secondary seal seat member having a first surface and a second surface, and secondary seal spring means normally biasing said secondary seal seat member toward said gate member such that when the gate member is in said closed position an initial secondary seal is provided by said secondary seal seat member against said gate member at said first surface of the secondary seal seat member; said first surface and said second surface of the secondary seal seat member being exposed to fluid pressure resulting from pressure of fluid in the upstream flow passage when said primary seal means leaks fluid along the surface of the gate member, said second surface of the secondary seal seat member having an area exposed to such fluid pressure greater than the area of said first surface of the secondary seal seat member exposed to such fluid pressure whereby the fluid pressure from the upstream flow passage forces the secondary seal seat member against the gate member and establishes a secondary seal preventing flow along the surface of said gate member when said gate member is in the closed position and said primary seal means leaks; said primary seal seat member comprising an annular ring member having an enlarged ring-like body portion on the outside thereof, said secondary seal seat member comprising an annular ring member having a portion thereof extending over said enlarged body portion of the primary seal seat member to create therewith a chamber into which fluid can pass from the upstream flow passage upon leaking of the primary seal means, a surface of said chamber being said second surface of said secondary seal seat member.