Positive and Negative Bias Relays are designed for applications that require an output pressure that is the sum of a controlled input signal plus or minus a fixed bias. Fairchild's line up of biasing pneumatic relay products includes both positive biasing relays, such as the Models 15, 85D and 1500A and relays that handle both positive and negative biasing functions such as the Model 14.
Reversing Relays are designed for applications requiring an output that equals a manually preset spring load minus a variable signal pressure. These high quality units, such as the Model 25 and Model 2500A, combine excellent sensitivity with unusually high flow capacity. These Fairchild reversing pneumatic relays are ideally suited for a variety of precision control applications, including converting direct acting valves to reverse action, controlling opposite acting valves from a single transmitter, and cushioning cylinder loads.
Adjustable Ratio Relay
Fairchild's Model 21 is an Adjustable Ratio Pneumatic Relay, whereby the ratio of output pressure to signal pressure is infinitely adjustable. The adjustment range permits signal amplification of 1:30 or signal reduction of 30:1 by rotation of the ratio adjustment knob. The Model 21D is available with both input and output adjustable bias. Maximum input bias is 3 psig, with a maximum output bias of 9 psig.
Pneumatic Computing Relay
Designed for highly versatile control valve designed to perform a number of specialized functions, including averaging, differential, inverting, and totalizing, the Model 22 Pneumatic Computing Relay is a versatile Fairchild product. This high quality unit, which offers up to four inputs as well as positive and negative biasing over a broad range, is available in several configurations to meet most application requirements.
Snap Acting Relay
The Model 24 Snap Acting Relay is a highly accurate differential relay with snap-acting switching. The output of the unit will go to supply pressure when the signal is equal to or greater than the setpoint. The signal pressure must fall below the set point to return the output to zero. This pneumatic relay's Near Zero Throttling and Pilot Staging result in true snap-action in your application.
The Model 90 Low Pressure and Model 91 High Pressure Selector Relays are designed to select the lower or higher of two signal pressures to provide a continuous output pressure to a control device. The Model 90 and 91 are recommended for dead end or low flow service in critical applications such as control loops requiring precise, automatic monitoring of signal pressures.