Model P31

SKU: P31

Capacitance Probe, External Cage, Vertical

The Delta Controls Model P31 Capacitance Probe is primarily used in the chemical, petrochemical, refining, and other continuous process industries. The probe design can be tested, calibrated, and maintained without shutting down or disturbing the process. Common applications include heating fluid, interface position, tower bottoms, water knockout traps, etc.

The P31 is equipped with an external cage to the process vessel or tank. This cage is a vertical cylindrical pressure vessel containing the probe. Isolation valves are normally installed by the user between the cage connection ports and the process vessel or tank. This isolates the instrument from the process pressure, or partially full tank, for testing and calibration purposes without blow down or draining the process.

The P31 cage serves as the ground reference for the sensing rod. A signal linear to the liquid level or an interface position is generated for alarm or signal transmission outputs.


  • Inherent high gain sensitivity
  • Can be calibrated, tested, or inspected without disturbing a continuous process
  • Avoids problems due to turbulence and splashing
  • Works in highly corrosive service
  • Full scale 4-20 mA output signal change achievable over a few inches of level change


  • Working Pressure: +650 psig (+44.8 bar)
  • Working Temperature: ≤ +750 °F (+399 °C)
  • Insertion Length:10 ft (3 m)
  • Process Connection Orientation: Side/Bottom, Side/Side, Side/Side/Drain
  • Process Connection Spacing: 14.0 in to 150.0 in
  • Process Connection Threaded: 1.0 in to 2.0 in
  • Process Connection Flange:1.0 in to 2.0 in
  • Flange Rating:≤ 600 lb
  • Available Wetted Materials: Carbon steel, blended alumina ceramic, PTFE (other materials available)
  • Drain:Optional Drain (0.75 in NPT)

Required Ordering Information

  • Detailed model number
  • Tag or nameplate detail (if required)
  • Documentation & testing packages (if required, refer to Additional Resources in the product catalog)
  • Process fluid or material name
  • Process fluid or material dieletric constant
  • Maximum process temperature
  • Maximum process pressure
  • Upper and lower materials required for interface service

Additional Information


Capacitance Probe, External Cage, Vertical

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