Supervisory switch (For OS&Y valve) is used to monitor the open position of an outside screw and yoke gate valve. It contains visual switch indicators, adjustable length trip rod, two conduit entrances, bracket, etc.
It is a 3-position switch. When it is installed on the OS&Y valve, the valve is fully open and the trip rod of the switch is in the groove of the valve stem. Closing the valve will cause the trip rod to ride up out of the groove and activate the supervisory switch.