Actuation & Instrumentation
Bench Set
The bench set is the air-pressure range applied to a diaphragm or piston spring actuator (measured on the bench, with the valve unloaded) that produces the full rated travel from fully closed to fully open. A typical bench set is 0.2–1.0 bar (3–15 psi): at 0.2 bar the spring compression balances with the valve closed, at 1.0 bar the plug has travelled its full stroke.
Why it matters: the spring range must be matched to the forces the plug actually sees — the unbalance force from the pressure drop plus the packing friction. If the bench set is wrong for the service, the valve will not seat under load (leakage), will not reach full travel (inherent capacity lost), or will exert a permanent seat load that scores the seats.
Bench set is checked with the valve off-line using a pressure gauge and a travel indicator; it is one of the first things to verify when a "weak" or "lazy" valve is reported.