Positive Bias Booster Industrial Pneumatic (Air) Relay

The Precision Controls Division (PCD) of Marsh Bellofram Corporation has announced the global market introduction of the Type 72 series of positive bias booster pneumatic (air) relays, designed for use within industrial air pressure regulation and monitoring applications where high flow capacity is required, such as volume boosting; gas flow, tensioning, clutch and brake, and cylinder bucking control functions; and calendar roll, dancer roll and valve motor loading.  The Marsh Bellofram Type 72 series is available in four adjustable positive bias ranges, from 0 to 10 psi (0 to 0.7 BAR); and from to 2 to 150 psi (0.1 to 10.3 BAR), all with exceptionally high flow capacity of up to 50 SCFM (1400 LPM) and with minimal pressure droop, as well as quick response to minute changes in downstream pressure. 

An optional high-relief version (Type 72HR) is also available.   The standard signal-to-output ratio is 1:1, but 1:2, 1:4 and 1:6 ratios are available on special request.  Output is virtually unaffected by supply pressure changes.    Design of the Type 72’s balanced supply valve incorporates the use of a Bellofram patented internal rolling diaphragm, making the relay virtually immune to changes in supply pressure, while offering reliable performance over millions of cycles and a simple, maintenance-free design. In addition, the relay can be both disassembled and serviced without removing it from the line.  

Output pressure is accurately maintained under varying flow conditions by means of an aspirator tube, which adjusts the air supply valve opening in proportion to flow velocity.  The dampening action of the aspirator tube maintains stable output pressure. Action of the integral baffle and aspirator tube also eliminates honking and buzzing noise.