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Hydraulic-over-air relay valves convert hydraulic modulated input pressure to proportional output air pressure in on- and off-highway applications. A common use would be to control an air-braked trailer with a hydraulically braked towing vehicle that has an air power source. A hydraulic vehicle component, such as a master cylinder or hydraulic control valve, delivers a given hydraulic input pressure, which sends a pilot signal to the relay valve to modulate air-brake pressure on the other end.
Designs include single, dual, and tandem. Single provides one hydraulic pilot port to control modulated air braking pressure; dual input features two independent ports, which can accept pilot pressure; tandem provides redundancy by using two independent pilot pressure ports. All accommodate air pressure to 150 psi and hydraulic pressure to 2000 psi and can be adjusted to operate at anywhere from a 3:1 to 21:1 hydraulic-to-air-pressure ratio.
MICO Inc., (507) 625-6426, www.mico.com