Pneumatic relays and volume boosters control output air flow and pressure in response to a pneumatic input signal. They can perform simple functions such as boosting or scaling the output, or use complex reversal, biasing, and math function operators.
Pneumatic relays and volume boosters are used in a wide variety of control functions. A pneumatic relay and volume booster can be used as an indicator, a logic relay, or a ratio relay. An indicator relay is typically composed of a two-position valve that is actuated by a pneumatic signal from a remote sensor or transmitter. The indicator relay is used to indicate if there is an unsafe condition present in a particular variable or process. A logic relay is used for a variety of functions such as diverting the flow from one pipeline to another. These pneumatic relays and volume boosters can be the building blocks for more complex pneumatic logic circuits. A ratio relay is a pneumatic switch that can perform tasks based on a predetermined ratio, such as addition, subtraction, biasing, and reversing. A pneumatic reducing relay is a ratio relay capable of reducing the output pressure based on a particular input to output ratio. An air flow switch is used as a volume booster, using a low flow pneumatic signal to produce an output pressure with a higher flow capacity. An air pressure switch uses adjustable set points that are tripped when the pneumatic signal pressure increases or decreases.
Pneumatic relays and volume boosters are commonly used to switch air signals from one source to another, supplying pressure to or exhausting pressure from a particular line or control device, and providing initiation of a control function. Pneumatic relays and volume boosters can also be used as an interface between pneumatic and electric circuits. An electric pneumatic switch is an air switch that is electrically operated to control air flow input or output. Pneumatic relays and volume boosters are also used as safety switches that can open safety valves in an emergency or trigger an alarm while shutting down other valves to protect the overall system.