Model 85D Multi-Stage Biasing Relay

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The Fairchild 85D Multi-Stage Biasing Relay is a precision control combining the sensitivity of a precision pressure regulator with psitive biasing capability. This compact, pilot-operated device offers unusually high output capacity with minimal air consumption, while providing excellent protection against supply or output pressure variations.


  • 2 Stage Pilot Operation allows precise control of set points.
  • 14 SCFM flow capacity in a small size unit.
  • Low air consumption preserves air and other costly gases.
  • Compact size permits installation where space is limited.
  • Available in 1/8”, 1/4” and 3/8” port sizes.
Operating Principles

The versatile Fairchild 85D is recommended for use in systems requiring precision pressure maintenance and instrument biasing, in dead end service and instrument panel supply applications.

The basic mathematical expression for the Model 85D is PO = PS + K where PO is output pressure, PS is signal pressure and K is the spring constant.


Maximum Supply Pressure
250 psig, [17.5 BAR], (1750 kPa)
Recommended Operating Supply Pressure
150 psig, [10 BAR], (1000 kPa)
Maximum Signal or Output Pressure
150 psig, [10 BAR], (1000 kPa)
Flow Capacity
14 SCFM (23.8 m³/HR) @ 100 psig, [7.0 BAR], (700 kPa) supply, 20 psig, [1.5 BAR], (150 kPa) setpoint
Exhaust Capacity
2.5 SCFM (4.25 m³/HR) where downstream pressure is 5 psig, [.35 BAR], (35 kPa) above setpoint
Supply Pressure Effect
Less than 0.2 psig, [.014 BAR], (1.4 kPa) for 100 psig, [7.0 BAR], (700 kPa) change in supply pressure
Pressure Change Under Flow Conditions
Less than 0.1 psig, [.007 BAR], (.7 kPa) from dead end service to 10 SCFM (17 m³/HR)
(Set pressure 10 psig, [.7 BAR], (70 kPa), supply pressure 100 psig, [7.0 BAR], (700 kPa)
Air Consumption
Less than .1 SCFM (.17 m³/HR)
Ambient Temperature Limits
-40°F to +200°F, (-40°C to 93.3°C)
Materials of Construction
Body: Aluminum
Trim: Aluminum, Stainless Steel, Brass
Diaphragms: Buna N and Dacron

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

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