Bellows-Type Steam Trap:

A bellows-type steam trap is described in Figure. The operation of this trap is controlled through the expansion of the vapor of a volatile liquid that is enclosed within a bellows-type element.

Steam enters the trap body and heats the volatile liquid within the sealed bellows, by causing expansion of the bellows.

Figure: Bellows-Type Steam Trap

The valve is attached to the bellows in like a way in which the valve closes while the bellows expands. A valve remains closed, trapping steam within the valve body. Since the steam cools and condenses then the bellows cools and contracts, thus opening the valve and permitting the condensate to drain.