Pressure responsive two-way shut-off valve

Abstract

A shut-off valve for use with high pressure gas cylinders is disclosed which is adapted to automatically retain a residual pressure in the cylinder. The valve includes a check plug axially moveable within the housing which has a hard sealing surface, for establishing high pressure seals and a soft sealing surface for establishing low pressure seals. The plug is spring-biased into the closed position with force selected so that it automatically closes and seals the interior of the cylinder once the gas pressure in the cylinder drops to or below a predetermined threshold pressure. The plug, in combination with the valve seat, forms pressure drop zone upstream and downstream of the sealing surfaces which reduce the pressure and gas flow velocities past the sealing surfaces during the initial phases of the opening and the final phases of the closing of the valve sufficiently to prevent high pressure and/or high gas flow velocities from damaging or destroying the sealing surfaces irrespective of the gas flow direction through the valve. The valve includes an actuating mechanism for manually opening and closing the valve against high pressure by appropriately turning a handwheel. A tamper proof opening key is provided which cooperates with the opening mechanism in the vicinity of the handwheel so that the check valve can be opened manually for recharging the cylinder with high pressure gas.