A thermodynamic steam trap (see Figures 10-26 and 10-27) contains only one moving part, a hardened stainless-steel disc that functions as a valve. Because of its construction simplicity, this is an extremely rugged trap and is especially well suited for service on medium- and high-pressure steam lines operating under pressures up to 600 psig. The minimum operating pressure for some makes of these traps is as low as 3.5 psig.
Thermodynamic steam traps are small, unaffected by water hammer, and can be mounted in any position. The operating principles of a thermodynamic steam trap are illustrated in Figure 10-28.