The Closed Position Indicator, also known as a Control Position Indicator (CPI), switch is a mechanically activated micro-switch for monitoring the position of the gas valve.
The unit is a mechanically activated switch for monitoring the position of the valve plate. When valve is closed, plate is in contact with valve seat. Switch rod is pushed and electric contact is switched in configuration 1-3. When valve opens, plate leaves seat and frees the rod, so that contact switches in configuration 1-2, under the action of a return spring. Norm EN 161 specifies that switch has to commute when the plate is within 1mm to its closed position, so the CPI is an item to detect the closed status, not the completely open one.