Pneumatic, electric or manual actuation — how do I choose?

Choose on cycle count and on what utilities you already have at the machine. A valve that opens twice a shift and a valve that cycles with every wafer are different products even at the same size and flange.

Pneumatic is the default for anything that cycles automatically. It is fast, it has no motor to overheat, and a spring-return version fails to a defined state when air is lost — which is the property that actually matters in a safety interlock. The requirement people underestimate is the air itself: the valve needs clean, dry compressed air at the pressure on the data sheet, and a plant air line carrying oil or water will destroy the actuator seals long before the vacuum seal wears.

Electric suits places where compressed air is not available or where you need position feedback and intermediate positions without a separate positioner. It is slower and generally more expensive per unit, and on power loss it stays where it was unless you specify a fail-safe version — which is exactly the opposite behaviour to a spring-return pneumatic, and worth deciding deliberately rather than by default.

Manual is right where the valve is set once during setup and then left alone — isolating a gauge, a roughing branch, or a vessel that is opened for service on a schedule. It is the cheapest and has nothing to fail. It becomes wrong the moment somebody has to operate it inside a process cycle, because it will eventually be operated in the wrong order.

For all three, specify the position indication you need separately from the actuation. Limit switches on a pneumatic valve are what let the controller know the valve actually moved rather than that it was commanded to move — the difference between those two is where a surprising number of process faults live.

One more that affects service life more than the actuator choice: cycle rate against the seal. A valve rated for millions of cycles in a clean gas line will not deliver that in a line carrying process particulate, because the seal face is where particles collect. If your duty is dirty, ask about the seal arrangement rather than about the cycle rating.