Xylem Bell & Gossett Hoffman Speciality Series Engineering Data Manual page 6

Thermostatic Bellows Type Trap
Advantages
Sub-cools condensate usually 10° to 30°F.
Normally open at start-up to provide fast
air venting.
Follows steam saturation curve to operate
over wide range of conditions.
Brass bodies.
Self draining.
Energy efficient.
Compact size and inexpensive.
Fast response to changing conditions.
Fail open models.
Disadvantages
Water hammer can damage bellows.
Superheat can damage bellows if it
exceeds trap temperature rating.
Pressure limit of 125 psig.
Cooling leg required in some applications.
INTERNAL
FLEXIBLE DIAPHRAGM
OUTLET
THERMOSTATIC TRAP
Thermostatic traps are normally open. This
allows fast venting of air during start-up.
Applications
Radiators, convectors, unit heaters.
Cooking kettles.
Sterilizers.
Heating coils.
Tracer lines.
Evaporators.
NOTE: A solid fill expansion element (see
Hoffman Specialty 17K) thermostatic trap
should be used where water hammer (cavita-
tion) may occur.
INLET
OUTLET
THERMOSTATIC TRAP
Cold condensate during start-up drains
through the trap. As temperatures reach 10°
to 30° F of saturation, the trap closes.
During operation, thermostatic traps find an
equilibrium point to drain condensate approxi-
mately 10° to 30°F below saturation at a con-
tinuous flow.
INTERNAL
FLEXIBLE DIAPHRAGM
INLET
7