Type 72 and Type 72HR Positive Bias Booster Pneumatic Air Relays

Type 72 and Type 72HR Positive Bias Booster Pneumatic Air Relays are positive bias booster pneumatic relays are used when high flow capacity is required. Offered in four adjustable ranges with exceptionally high flow capacity of up to 50 SCFM (1400 LPM) with minimal pressure droop, output pressure of the Type 72 & Type 72HR are accurately maintained under varying flow conditions by means of an aspirator tube, which adjusts the air supply valve opening in proportion to flow velocity.

A balanced supply valve utilizing a Bellofram patented internal rolling diaphragm makes the relay virtually immune to changes in supply pressure, while offering reliable performance over millions of cycles. Simple design makes maintenance easy, and the relay can be serviced without removing it from the line. The standard signal-to-output ratio is 1:1, but 1:2, 1:4 and 1:6 ratios are available on special request. An optional high-relief version (72HR) is also available.



  • Four Adjustable Positive Bias Ranges from 0-10 PSI (0-0.7 BAR) to 2-150 PSI (0.1-10.3 BAR)
  • Quick Response to Minute Changes in Downstream Pressure
  • Dampening Action of Aspirator Tube Maintains Stable Output Pressure
  • Output Virtually Unaffected by Changes in Supply Pressure
  • Honking and Buzzing Eliminated by Action of Integral Baffle and Aspirator Tube
  • Can Be Disassembled and Serviced Without Removing from Line
  • Also Available in a High Relieving Version (72HR)


  • Gas Flow Control
  • Tensioning Control
  • Clutch and Brake Controls
  • Volume Boosting
  • Dancer Roll Loading
  • Calendar Roll Loading
  • Cylinder Bucking Control
  • Valve Motor Loading