Patent ID: 6871834

Claim:
A circuit for operating a valve closure system that has an air motor for turning a handle of a tank valve, the circuit comprising: a first valve that has a first port for connection to an air source and a second port, and that is selectively operable to a first position for closing the first port to the second port and to a second position for opening the first port to the second port; and a second valve that has a first port connected to the second port of the first valve, a second port for connection to a port of the air motor that operates the air motor, and a third port for connection to an emergency air source, and that, in the absence of delivery of emergency air to the third port, opens the first port to the second port to allow bi-directional airflow between its first port and its second port while closing the third port to both its first and second ports, and upon delivery of emergency air to the third port forces the third port to open to its second port regardless of whether its second port is open or closed to its first port.