Our extensive line of pneumatic relays serves a multitude of control applications: positive biasing relays, positive and negative biasing relays, infinitely adjustable ratio relays, reversing relays, averaging and computing relays, high and low pressure selectors, and high and low pressure limiting relays.

Lower Pressure Selector Relay (M90)
The Model 90 Low Pressure Selector Relay is designed to select the lower of two signal pressures to provide a continuous output pressure to a control device. The Model 90 is recommended for dead end or low flow service in critical applications such as control loops requiring precise, automatic monitoring of signal pressures. 
Higher Pressure Selector Relay (M91)
The Model 91 High Pressure Selector Relay is designed to select the higher of two signal pressures, and to provide a continuous output pressure (or pressure range) to a controller. The ability to precisely control pressure switching and pressure monitoring functions make the Model 91 the logical choice in dead end or low flow applications such as precision control loops. 
Snap Acting Relay (M24)
The Model 24 Snap Acting Relay is a highly accurate differential relay with snapacting 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 snapaction in your application. 
Computing Relay (M22)
The Model 22 Pneumatic Computing Relay is a highly versatile control valve designed to perform a number of specialized functions, including averaging, differential, inverting, and totalizing. 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. The combination of multiple configuration options and accurate response characteristics make the Model 22 the ideal choice in a variety of applications with specific input/output requirements such as override or multielement control, or as an ONOFF valve. When used as an ONOFF valve, the Model 22 may open or close a pneumatic circuit, moving rapidly to a full open or a full closed position when signal pressures deviate from set point. In the full open position, the valve passes full supply pressure without modulation or regulation. The function is achieved by connecting output pressure to the signal chamber. This connection forms a feedback loop so that, once flow is started, the valve is driven wide open. The relay always goes full open or full closed when conditions are as shown in the diagrams on the Fairchild specification sheets and catalog. 
Adjustable Ration Relay (M21)
The Model 21 Adjustable Ratio pneumatic relay has a signal chamber lever arm, 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 which moves the fulcrum. . Output pressure is a function of signal pressure times the ratio of lever arm lengths on either side of the fulcrum. Bias may be introduced by means of the set screws. 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. The basic mathematical expression for the bias in this relay is Po = (PsK1) R+K2, where Po = Output pressure, Ps = Input signal, R = Ratio of setting, K1= Input bias, () only, and K2 = Output bias, (+) only. 
Reversing Relay (M25)
The Model 25 Reversing Relay is designed for applications requiring an output that equals a manually preset spring load minus a variable signal pressure. This high quality unit combines excellent sensitivity with unusually high flow capacity. The Model 25 is 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. The basic mathematical expression for the Model 25 is PO = K  PS where PO is output pressure, PS is signal pressure and K is the spring constant. 
High Flow Reversing Relay (M2500A)
The Model 2500A Bias Reversing Relay provides an outlet pressure that decreases in direct proportion to increases in input signal. The input signal that acts on the Diaphragm Assembly opposes the Range Spring force and closes the Supply Valve to decrease output pressure, according to the formula (Po = K  Ps); where Po is output pressure, K is the spring constant, set by the screw, and Ps is signal pressure. The M2500A pneumatic relay delivers this performance at a flow capacity of 150 SCFM (255 m3/HR), to provide fast response and tight control over your application. 
Positive and Negative Bias Relay (M14)
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 Model 14 Biasing Pneumatic Relay provides versatility in its ability to provide either positive or negative biasing in a single unit. The output of the Model 14 relay is the sum of the spring bias, set with the Range Screw, plus a pneumatic input signal. (Po = Ps � K); where Po is output pressure, Ps is signal pressure, and K is the combined spring constant. 
Positive Bias Relay (M15)
The Model 15 Positive Bias Relay is designed for applications that require an output pressure that is the sum of a controlled input signal plus a fixed bias. This pneumatic relay provides an output pressure that represents the input signal pressure plus a preset bias. Mathematically Po = Ps + K where Po is output pressure, Ps is signal pressure and K is the spring constant. This unit, available in several bias range configurations to meet a variety of output requirements, offers excellent sensitivity and high flow capacity in a small volume. The Fairchild Model 15 Pneumatic Biasing Relay is well suited to a variety of control applications, including range shifting, and tension control, and pressure control from a remote location. 
MultiStage Positive Bias Relay (M85D)
The Model 85D MultiStage Biasing Relay is a precision control combining the sensitivity of a precision pressure regulator with positive biasing capability. This compact, pilotoperated device offers unusually high output capacity with minimal air consumption, while providing excellent protection against supply or output pressure variations. The versatile Model 85D is recommended for use in systems requiring precision pressure maintenance and instrument biasing, in dead end service and instrument panel supply applications. The basic mathematical expression for the Fairchild Model 85D is PO = PS + K where PO is output pressure, PS is signal pressure and K is the spring constant. 
High Flow Positive Bias Relay (M1500A)
The Model 1500 Positive Bias Relay is designed for applications that require an output pressure that is the sum of a controlled input signal plus a fixed bias. This pneumatic relay provides high output flow at an output pressure that represents the input signal pressure plus a preset bias. The output of the relay is the sum of the spring bias, set with the Range Screw, plus a pneumatic input signal. (Po = Ps + K); where Po is output pressure, Ps is signal pressure, and K is the spring constant set by the Range Screw.