Model 15 Positive Relay

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The Fairchild 15 Positive Bias Relay is designed for applications that require an output pressure that is the sum of a controlled input signal plus a fixed bias.


  • The Fairchild 15 is sensitive to 1/4" Water Column variation which permits use in precision applications.
  • A Balanced Supply Valve minimizes the effects of supply pressure variation.
  • Aspirator Tube minimizes downstream pressure droop under flow conditions.
  • Flow of up to 40 SCFM with 100 psig Supply at 20 psig Setpoint allows use in applications requiring high flow capacity.
  • A Separate Control Chamber isolates the diaphragm from the main flow, eliminating hunting and buzzing.
  • Mounting Bracket available.
Operating Principles

The Fairchild 15 Positive Bias Relay provides an output pressure that represents the input signal pressure plus a preset bias. Mathematically Po = Ps + K where Po is output pressure, Ps is signal pressure and K is the spring constant. This unit, available in several bias range configurations to meet a variety of output requirements, offers excellent sensitivity and high flow capacity in a small volume.

The unit is well suited to a variety of control applications, including range shifting, and tension control, and pressure control from a remote location.


Supply Pressure
250 psig, [17.0 BAR], (1700 kPa) Maximum
Flow Capacity (SCFM)
40 SCFM (68 m³/HR) @ 100 psig, [7.0 BAR], (700 kPa) supply and 20 psig, [1.5 BAR], (150 kPa) setpoint
Exhaust Capacity (SCFM)
5-1/2 SCFM (9.4 m³/HR) where downstream pressure is 5 psig, [.35 BAR], (35 kPa) above 20 psig, [1.5 BAR], (150 kPa) setpoint
Signal or Output Pressure
150 psig, [10.0 BAR], (1000 kPa) Maximum
Supply Pressure Effect
Less than 0.1 psig, [.007 BAR], (.7 kPa) for 100 psig, [7.0 BAR], (700 kPa) change in supply pressure
Less than 1/4” (.64 cm) Water Column
Pipe or Panel
Ambient Temperature
-40°F to +200°F, (-40°C to 93.3°C)
Hazardous Locations
Acceptable for use in Zones 1 and 2 for gas atmosphere; Groups IIA and IIB and Zones 21 and 22 for dust atmospheres
Materials of Construction
Body and Housing: Aluminum Alloy
Trim: Stainless Steel, Brass, Zinc Plated Steel
Diaphragms: Buna A and Dacron

Catalogue PDF: application/pdf
Operational PDF: application/pdf
Located in: Relays

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