Balanced sealing means

Claim 1

IN A DEVICE FOR CONTROLLING FLUID FLOW, ANNULAR STATIONARY SEAT MEANS, ANNULAR VALVE MEANS ALIGNED WITH THE AXIS OF THE SEAT MEANS AND MOVABLE ALONG SAID AXIS TOWARD AND AWAY FROM THE SEAT MEANS BETWEEN CLOSED AND OPEN POSITIONS, BOTH OF SAID MEANS FORMING COOPERATING METAL VALVE WORKING SURFACES, ONE O SAID MEANS COMPRISING AN ASSEMBLY INCLUDING TWO ANNULAR PARTS, SAID PARTS BEING FORMED TO PROVIDE OPPOSED ANNULAR CLAMPING FACES, A RELATIVELY THIN ELONGATED ANNULAR SEAL MEMBER FORMED OF RESILIENT MATERIAL HAVING ITS ELONGATED SIDE PORTION DISPOSED AND CLAMPED BETWEEN SAID FACES AGAINST LEADKAGE THEREBETWEEN, WITH A PERIPHERAL EDGE PORTION OF THE SEAL MEMBER PROJECTING FOR SEALING CONTACT WITH THE VALVE WORKING SURFACE OF THE OTHER ONE OF SAID MEANS, SAID ASSEMBLY BEING FORMED TO ESTABLISH FLIUD PRESSURE COMMUNICATION BETWEEN THE REGION AT THE OTHER PERIPHERAL EDGE PORTION OF THE RESILIENT SEAL MEMBER AND SAID DOWNSTREAM SIDE OF THE DEVICE TO PROVIDE A PRESSURE DIFFERENTIAL ACROSS SAID SEAL MEMBER BETWEEN SAID PROJECTING PERIPHERAL EDGE AND SAID OTHER PERIPHERAL EDGE WHEN SAID PROJECTING PERIPHERAL EDGE IS EXPOSED TO UPSTREAM PRESSURE WHILE THE CLAMPING ENGAGEMENT OF SAID CLAMPING FACES AGAINST THE SIDES OF SAID SEAL MEMBER PREVENTS ENTRY OF UPSTREAM PRESSURE TO SAID REGION AT THE OTHER PERIPHERAL EDGE PORTION, SAID OTHER PERIPHERAL EDGE PORTION BEING IN FLUID-TIGHT ISOLATION FROM THE UPSTREAM SIDE OF THE DEVICE.