Valve

Claim 1

A VALVE ADAPTED TO PRODUCE A PRESSURE SEAL, SAID VALVE COMPRISING A HOUSING HAVING A WALL DEFINING AN ENCLOSED CYLINDRICAL CHAMBER, A CYLINDRICAL PASSAGE OF SMALLER DIAMETER THAN SAID CHAMBER INTERSECTING SAID CHAMBER THEREBY DEFINING A TRANSVERSE FLOW PASSAGE THROUGH SAID CHAMBER, A HOLLOW PISTON COMPRISING AN AXIALLY RIGID RESILIENT CYLINDER HAVING A RADIALLY EXPANSIBLE WALL PORTION EXPANSIBLE INTO SEALING RELATIONSHIP WITH SAID CHAMBER WALL, SAID PISTON HAVING A SLIDING FIT WITH AND BEING SHIFTABLE AXIALLY IN SAID CHAMBER BETWEEN A FIRST POSITION WITHDRAWN FROM ACROSS SAID FLOW PASSAGE AND A SECOND POSITION IN BLOCKING POSITION ACROSS SAID FLOW PASSAGE, SAID HOLLOW PISTON FITTING CLOSELY WITHIN SAID CHAMBER TO PROVIDE A SUBSTANTIAL ANNULAR AREA OF ENGAGING SEAL SURFACE BETWEEN SAID PISTON AND THE CHAMBER WALL, FLUID PRESSURE ACTUATED MEANS SHIFTABLE AXIALLY IN SAID CHAMBER AND HAVING A PLUNGER ENGAGING WITHIN SAID HOLLOW PISTON, MEANS INTERPOSED BETWEEN SAID PLUNGER AND SAID PISTON WALL PORTION FOR RADIALLY EXPANDING SAID PISTON WALL PORTION, AND MEANS FOR ADVANCING SAID FLUID PRESSURE ACTUATED MEANS, SAID PLUNGER ADVANCING THEREWITH TO MOVE SAID HOLLOW PISTON TO SAID BLOCKING POSITION, SAID EXPANSIBLE WALL PORTION OF SAID PISTON THEREAFTER BEING EXPANDED BY SAID MEANS INTERPOSED BETWEEN SAID PLUNGER AND SAID PISTON WALL PORTION TO SEAL SAID FLOW PASSAGE.