This picture shows the pneumatic operator in a GE FK-439 oil circuit breaker. There are 2 air valves in this scheme; the lower valve is the operating valve and functions to close the circuit breaker. The upper valve is used in a fast trip scheme to open the breaker if closed in on a fault and a trip free operation is required. The upper valve does not come into play in a normal close operation. I have found the upper valve stuck in place due to moisture corrosion on units due to inactivity. If the air pressure is bled down, the spool should be moveable when pushed up from the bottom. If not, the valve needs to be changed.


The lower valve as stated is the unit that operates to allow air to go into the closing cylinder. The function of the solenoid is magnetically latched after being energized until the closing cylinder completes its stroke. At the top of the cylinder stroke is a cutoff switch that operates another coil in the valve to cancel the magnet holding the valve open. Once this is energized, the valve spool shifts back to the ready position, and allows the valve and cylinder to exhaust its air from the previous operation.

The auxiliary valve and main valve are different but look the same from the outside. When changing the air valve or replacing the operating coil, the orientation of the coil in the valve is critical as well as the polarity of the windings. If the coil is not put in correctly, the valve may not fire, if the polarity is incorrect, the valve will not latch to allow the breaker to close. Additionally, there is an internal kick off spring that has to be matched to the closing mechanism operating pressure. Any of these items can create what appears to be a trip free operation. These valves typically have 3 or 4 windings on the same coil spool so marking the wiring is critical before removal.

If you see coil movement during a close operation but the valve fails to fire, chances are the coil is in upside down. If the valve fires but does not close the breaker, it is likely a failure of the valve to magnetically latch. This can be caused by the wrong operating coil, the wrong operating voltage, the incorrect winding polarity, the wrong coil winding being used, or the wrong kick off spring for the operating air pressure. Problems with this mechanism can be very frustrating if you don't understand it.