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Balanced Pressure Thermostatic Traps
Operation / Characteristics / Hoffman Specialty Product Features / Primary Applications

Thermostatic steam traps reduce start-up times and improve overall efficiency.

Balanced Pressure Thermostatic Traps use a special bellows diaphragm. The diaphragm is designed to open in response to pressure and temperature to discharge air and condensate, and to close against passage of steam. The temperature at which a Thermostatic Trap opens is variable, but is 10 to 30° F below saturated steam temperature for the existing pressure.

This type of trap is small, simple in construction, size and weight, and has adequate capacity for various applications, especially in low-pressure heating systems.

Operation of Thermostatic Traps:

Thermostatic traps are normally open allowing fast venting of air during start-up.



During start-up, cold condensate drains through the trap. As temperatures reach 10° to 30° F of saturation, the thermostatic bellows element closes the trap.

During operation, thermostatic traps find an equilibrium point to drain condensate approximately 10° to 30° F below saturation at continuous flow.

Characteristics of Thermostatic Traps:

  • 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.
  • Self-draining.
  • Energy efficient.
  • Fast response to changing conditions.
  • Fail mode is open.
  • Water hammer can damage bellows.
  • Superheat can damage bellows if it exceeds trap temperature rating.
  • Cooling leg required in some applications.

Features of Hoffman Specialty Thermostatic Traps:

  • Brass bodies provide resistance to moderate water hammer and chemical attack.
  • Stainless steel Dura-Statâ modules are easily replaced without disturbing piping connections.
  • Compact size reduces installation space requirements.
  • Inexpensive purchase price.
  • Range of seat pressures available - up to 125 psig.

Primary Applications of Thermostatic Traps:

  • Radiators, convectors, unit heaters.
  • Cooking kettles.
  • Sterilizers.
  • Heating coils.
  • Tracer lines.
  • Evaporators.
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