There are several types of thermostatic steam traps. In general, these traps are more compact and have fewer moving parts than most mechan-ical steam traps. The operation of a bellows-type thermostatic trap is controlled by expansion of the vapor of a volatile liquid enclosed in a bellows-type element. Steam enters the trap body and heats the volatile liquid in the sealed bellows, thus causing expansion of the bellows. The valve is

Figure 13-34.-Bucket-type steam trap.

attached to the bellows in such a way that the valve closes when the bellows expands. The valve remains closed, trapping steam in the trap body. As the steam cools and condenses, the bellows cools and contracts, opening the valve and allow-ing the condensate to drain.

The impulse and bimetallic steam traps are two examples of those that use the thermostatic principle.