Bellofram Type 75 Pneumatic Air Relay

The Marsh Bellofram Type 75 Pneumatic Air Relay uses signal pressure to precisely maintain output pressure over a vast range of flow and supply pressure variations. Under these varying flow conditions, output pressure is controlled by use of an aspirator tube, which adjusts the air supply valve opening in accordance with flow velocity. A balanced supply valve, using a patented Marsh rolling diaphragm, makes the relay virtually unaffected by changes in supply pressure, with reliable operation over millions of cycles.

The basic Type 75 relay provides superior precision, along with high forward flow rates. In addition, units are available with an internally spring mounted fixed negative bias, with a formula that is particularly useful for obtaining zero pressure from pneumatic devices such as I/P transducers, which cannot normally be adjusted this low, as well as obtaining higher outputs from such devices. The design and construction of the Type 75 relay allow minimal maintenance, with units able to be serviced without removing it from the line, avoiding downtime. Signal to output pressure ratios of 1:1, 1:2, 1:4 and 1:6 are available. Maximum output is 150 PSIG (10.3 BAR).