How does a volume booster affect actuator response time & size, given the "hit" during functional testing when moving the positioner screw?

The primary objective was that using a volume booster had no direct impact on actuator size. Actuator sizing is essentially determined by the valve’s needed torque/thrust, which is determined by the force produced by compressed instrument air in the actuator chamber. The actuator size is influenced by the chamber’s effective area and the minimum air pressure under normal working conditions.

Function of Volume Booster

Volume boosters provide more capacity than positioners, lowering response time by filling the actuator chamber faster.

Use of Booster and Positioner Together

Combining a booster with a positioner improves pneumatic output precision for minor changes in control input. The positioner serves as the booster’s pilot, supplying the necessary air flow to provide precise and stable reaction, particularly during minor control input adjustments.

Response Time and Overshoot

The diagram shows the typical pneumatic output response to a step change in set point. T63 and T86 are two often used parameters for measuring response speed. When a booster is used to reduce response time, overshoot may or may not occur, suggesting that there is more air delivered to the actuator than is required to reach the set point.

Impact on Actuator and Valve

Actuators and valves can handle higher supply pressures than the maximum bench range. In SAMSON 3277 type actuators, for example, the maximum supply pressure exceeds the bench range by 3 bar for fail-open & 6 bar for fail-close operations in On/Off services. There are no additional considerations required as long as these limits are met and the valve body can sustain actuator thrust at maximum supply pressure.

It emphasizes the complexities of maximizing control valve performance & maintaining compatibility with various system components.