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Hoffman Specialty Products General Catalog
8200 N. Austin AveMorton GroveMorton GroveIL 60053IL 60053USAUSATel 847 966-3700Tel 847 966-3700Fax 847 965-8379Fax 847 965-8379
Series 315 PNT and Series 240 PNT Pneumatic Temperature Control Pilot
Operation / Characteristics / Hoffman Specialty Product Features / Primary Applications

Pneumatic temperature control pilots consist of a brass or stainless steel bulb temperature sensor that operates a valve controlling an air signal. These pilots may be used with diaphragm valves to control temperature only. Or, they may be used with pressure pilots to provide both temperature and pressure control.

Operation of Pneumatic Temperature Control Pilots:

When the pneumatic temperature pilot senses a temperature below its set point, it delivers an air signal to the air pilot based on the sensed temperature. This air signal becomes the air pilot loading force. If the main valve downstream pressure is below the air pilot loading force, the pilot valve diaphragm is no longer balanced. The air pilot valve opens and inlet pressure is passed through the air pilot to the signal line.

Combination of Air-Pressure and Pneumatic Temperature Control


As the sensed temperature rises to the pneumatic temperature pilot set point, the temperature pilot valve closes and lowers the loading force to the air pilot. When the loading force decreases below the downstream pressure, the air pilot begins to close. Less steam passes through the air pilot to the signal line to the main valve, shutting off steam flow to the main valve diaphragm. The steam trapped under the main valve diaphragm bleeds off through an orifice, allowing the main valve to close.

Characteristics of Pneumatic Temperature Control Pilot:

  • Pneumatic temperature control pilots may be combined with pressure pilots to provide multiple functions.
  • Provide fast response over a minimal temperature change.
  • Easily adjusted.
  • Can be remotely located from the Main Valve and Air Pressure Control Pilot.
  • Not affected by ambient temperature.
  • Will not operate if air supply is interrupted.
  • More costly than self-contained valves.

Features of Hoffman Specialty Series 315 PNT and Series 240 PNT Pneumatic Temperature Control Pilots:

  • Lightweight, compact size prevents strain on mounting pipes.
  • Selection or components can provide either fail open or fail closed design.
  • Optional wells allow bulb removal without draining system.
  • Accuracy of control 4 F ( 2.2 C) with system recirculation.
  • Series 315 PNT:
    • For shop quality air:
      • Minimum 15 psig (1.0 bar).
      • Maximum36 psig (2.4 bar).
    • Air consumption 0.50 scfm (0.014 m3).
    • No limit to length of capillary.
    • Bi-metallic temperature sensing.
    • Temperature control ranges:
      • 50 to 300 F (10 to 149 C).
      • 200 to 450 F (93 to 232 C).
  • Series 240 PNT:
    • For control quality air
      • Minimum 15 psig (1.0 bar).
      • Maximum30 psig (2.1 bar).
    • Low air consumption 0.008 scfm (0.00022 m3).
    • Capillary length 6 ft. (1.8m).
    • Copper sensing element.
    • Temperature control range:
      • -20 to 240 F (-7 to 116 C).
    • Ambient Temperature range:
      • 40 to 150 F (4 to 66 C).
    • Signal range
      • 0.5 psig (0.035 bar) minimum outlet pressure.
      • To within 0.5 psig (0.035 bar) of supply pressure.

Primary Applications of Pneumatic Temperature Control Pilot:

  • Applications with rapidly changing load requirements.
  • Storage tanks
  • Instantaneous heaters.
  • Shell and tube heaters.
  • Aftercoolers.
  • Engine jacket cooling.
  • Process temperature control.
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