Safety cut-off valve requiring reset by pressure equalization

Claim 1

IN A SAFETY VALVE, A HOUSING HAVING AN INLET FLUID CONNECTION AT ONE END, AN OUTLET FLUID CONNECTION AT THE OTHER END AND A PASSAGE EXTENDING BETWEEN THE INLET AND OUTLET FLUID CONNECTIONS, A SAFETY VALVE CHAMBER IN THE PASSAGE HAVING A SAFETY VALVE SEAT AT THE END OF THE CHAMBER TOWARD THE OUTLET CONNECTION, A SAFETY VALVE IN THE CHAMBER ADAPTED IN CLOSED POSITION TO CLOSE AGAINST THE SEAT, SPRING MEANS BIASING THE SAFETY VALVE TOWARD OPEN POSITION, A LEAKAGE PORT BETWEEN OPPOSITE SIDES OF THE SAFETY VALVE REMAINING OPEN WHEN THE SAFETY VALVE IS CLOSED, A PLUG VALVE IN THE HOUSING BETWEEN THE INLET CONNECTION AND SAFETY VALVE CHAMBER, HAVING A CLOSED POSITION WHICH CLOSES FLOW THROUGH THE PASSAGE AND AN OPEN POSITION WHICH OPENS FLOW THROUGH THE PASSAGE AND HAVING A PRIMER POSITION, AND A PRIMER PORT CONNECTED FROM THE PASSAGE ADJACENT THE INLET CONNECTION THROUGH THE PLUG VALVE IN THE PRIMER POSITION TO THE PASSAGE ADJACENT THE OUTLET CONNECTION BEYOND THE SEAT OF THE SAFETY VALVE.