Flow sensing shutoff valve

Claim 1

A PRESSURE RESPONSIVE FLUID FLOW SHUTOFF DEVICE, SAID SHUTOFF DEVICE INCLUDING, IN COMBINATION, A HOUSING, SAID HOUSING HAVING AN INLET AND OUTLET, SAID INLET AND OUTLET BEING ADAPTED FOR CONNECTION INTO A FLUID PRESSURE LINE, A CHAMBER IN THE HOUSING, A VLAVE MEMBER IN THE CHAMBER MOVABLE BETWEEN A CLOSED POSITION, IN WHICH IT BLOCKS FLUID FLOW FROM THE INLET TO THE OUTLET, TO AN OPEN POSITION IN WHICH THE INLET AND OUTLET ARE IN COMMUNICATION THROUGH A FLUID FLOW PATH, SAID VALVE MEMBER HAVING A FIRST SURFACE RESPONSIVE TO FLUID PRESSURE WITHIN SAID HOUSING FOR MOVING THE VALVE MEMBER FROM THE CLOSED POSITION TO THE OPEN POSITION UPON THE INITIAL APPLICATION OF LINE PRESSURE AT THE INLET, SAID VALVE MEMBER HAVING A SECOND SURFACE RESPONSIVE TO DOWNSTREAM PRESSURE IN SAID PRESSURE LINE AND COOPERATIVE WITH SAID FIRST SURFACE TO MAINTAIN THE VALVE MEMBER IN THE OPEN POSITON, SAID VALVE MEMBER HAVING A THIRD SURFACE RESPONSIVE TO SAID LINE PRESSURE AT SAID INLET TO AUTOMATICALLY RETURN THE VALVE MEMBER TO THE CLOSED POSITION UPON A PREDETERMINED DROP IN DOWNSTREAM PRESSURE, SAID FIRST AND SECOND SURFACES TOGETHER BEING SUBSTANTIALLY EQUAL IN EFFECTIVE PRESSURE AREA TO SAID THIRD SURFACE.