Abstract: A thermostatic steam trap is disclosed in which a control chamber contains an insert enclosing a bellows adapted to force a valve member to a closed position in a direction opposite the normal flow of fluid through the trap together with self-centering means to center and align the valve member with respect to the valve seat.

Abstract: A valve body member and various insert assemblies usable with the body member to form steam traps of different types are disclosed in this application. The body member includes an internally threaded, generally cylindrical recess extending inwardly from an outer surface and terminating in an end face, an inlet passage communicating with the recess through a passageway terminating in the end face of the recess, and a discharge passage also communicating with the recess. An annular rib is formed on the end face of the recess around the passageway and includes a surface on which is seated a first sealing ring clamped in place by a first bearing surface of the particular insert assembly used to form the steam trap; an annular seat is formed on the outer surface of the body member around the cylindrical recess and this seat receives a second sealing ring which is clamped in place by a second bearing surface of the insert assembly.