Safety shutoff valve

When this type of valve is tripped, the flow is quickly stopped and an indicator disc tells the operator that the electrical circuit has been opened by a failure somewhere in the system. When the system failure has been corrected so that the circuit is again closed, the valve can be opened by the action of the hand lever. If, however, the system failure has not been satisfactorily corrected, the circuit will remain open and moving the hand lever will not open the valve, because the valve stem remains disengaged from the handle.