Actuation & Instrumentation
Booster (Volume Booster)
A volume booster (relay booster) is a pneumatic relay valve installed between the positioner output and the actuator. Its job is pure flow amplification: it senses the positioner's small output pressure and passes air from the supply — or exhausts to atmosphere — at a much higher flow capacity, while reproducing the same pressure.
Large actuators have big volumes to fill and vent. A positioner alone may move the signal pressure quickly but starve the actuator of actual air volume, making the valve sluggish on large step changes. The booster multiplies the air delivery rate without changing the pressure command, cutting stroking time dramatically.
Boosters are standard on large diaphragm cases and piston actuators, on split-range installations, and wherever fast response is specified. They are adjustable (some include a bypass needle and deadband tuning) and must be tuned with the positioner — an aggressive booster on a small actuator can amplify oscillation instead of curing it.