A thermostatic steam trap opens when which of the following occurs?

A thermostatic steam trap operates based on the principle of temperature sensitivity. The correct situation that causes it to open is related to the behavior of the bellows inside the trap. As temperature increases, the steam trap's sensing element (often a bellows or other expanding mechanism) reacts to the rise in temperature by causing the bellows to expand. This expansion triggers the mechanism that opens the trap, allowing condensate (liquid water) to escape.

In contrast, if temperature decreases, the bellows contract, which closes the trap and prevents steam from escaping. Therefore, the operation of the trap hinges on the expansion and contraction of the bellows in response to changing temperatures, making the contraction of the bellows when temperature drops a critical aspect to understand in its operation. This process effectively ensures that the system maintains efficient operation by properly managing condensate and preventing steam loss.