Why can a gate valve be baked to a higher temperature with the gate open than with the gate closed?
As the temperature of the valve body goes up, the O-ring softens. If the O-ring softens while it is being compressed – that is, with the gate closed – and then allowed to cool under compression, the O-ring will form flats instead of returning to its original circular cross section shape. The flats will not seal as good as a circular shaped O-ring. To avoid developing flats on an O-ring, gate valves should be baked in an open position.
