Multi-Stage Positive Bias Relay (M85D)

The Model 85D Multi-Stage Biasing Relay is a precision control combining the sensitivity of a precision pressure regulator with positive 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. The versatile Model 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 Fairchild Model 85D is PO = PS + K where PO is output pressure, PS is signal pressure and K is the spring constant.


  • Two Stage Pilot Operation
  • 14 SCFM flow capacity in a small size unit
  • Low air consumption
  • Compact size
  • Available in 1/8", 1/4" and 3/8" standard port sizes


  • Allows precise control of set points
  • Allows use in applications requiring high flow and/or fast response
  • Preserves air and other costly gases
  • Permits installation where space is limited
  • Versatility makes it easy to design into new and existing applications

See PUB103-070 for further information.

Multi-Stage Positive Bias Relay (M85D)