At startup, the trap is cold and the bimetal element is contracted. The coil spring holds the valve open, quickly discharging the initial cold air and condensate.

As the condensate temperature rises the valve begins to close, restricting condensate flow.

When the condensate temperature reaches the set temperature the valve closes, stopping condensate discharge. When the condensate temperature drops below the set temperature, the bimetal element contracts.

The coil spring opens the valve, re-allowing condensate to be discharged. In normal operation, the valve repeats this slight opening without fully opening.