Automatically responsive shutoff valve

Claim 1

A VALVE COMPRISING A VALVE HOUSING HAVING AN INLET PORT AND AN OUTLET PORT; A VALVE SEAT BETWEEN THE TWO PORTS; A VALVE MEMBER MOVABLE FROM AN OPEN POSITION AWAY FROM THE VALVE SEAT TO A CLOSED POSITION AGAINST THE VALVE SEAT; SPRING MEANS BIASING THE VALVE MEMBER TO ITS CLOSED POSITION; SAID VALVE MEMBER BEING DISPOSED WITH RESPECT TO THE INLET PORT SO THAT WHEN THE VALVE MEMBER IS IN ITS OPEN POSITION THE INLET PRESSURE IS APPLIED TO THE FRONT FACE OF THE VALVE MEMBER AND NORMALLY RETAINS THE VALVE MEMBER IN THE OPEN POSITION AGAINST THE ACTION OF SAID SPRING MEANS; A CHAMBER DELIMITED AT ONE END BY A WALL FORMED IN THE HOUSING; A VALVE STEM CARRIED BY THE VALVE MEMBER AND PASSING THROUGH SAID WALL INTO THE CHAMBER; SAID VALVE STEM CARRYING PISTON, DIVIDING SAID CHAMBER INTO A FIRST COMPARTMENT ADJACENT TO SAID WALL AND A SECOND COMPARTMENT REMOTE FROM SAID WALL; A FIRST COMMUNICATION PATH FOR COMMUNICATING THE PRESSURE AT THE FRONT FACE OF THE VALVE MEMBER TO SAID SECOND COMPARTMENT; A SECOND COMMUNICATION PATH FOR COMMUNICATING THE PRESSURE IN SAID SECOND COMPARTMENT TO SAID FIRST COMPARTMENT; A THIRD COMMUNICATION PATH FOR COMMUNICATING THE PRESSURE IN SAID FIRST COMPARTMENT TO THE REAR FACE OF THE VALVE MEMBER; AND CONTROL MEANS FOR CONTROLLING AT LEAST ONE OF SAID COMMUNICATING PATHS TO APPLY A FORCE ON THE REAR FACE OF THE VALVE MEMBER WHICH, WHEN ADDED TO THE FORCE OF SAID SPRING MEANS, IS SUFFICIENT TO MOVE THE VALVE MEMBER TOWARD ITS CLOSED POSITION.