Gate, angle, butterfly or pendulum — which vacuum valve do I need?

Pick on two things first: whether the valve has to isolate against full differential pressure, and whether it has to get out of the gas path when open. Those two questions eliminate most of the catalogue before you ever look at price.

Gate valves (also called slide valves) move a plate fully clear of the bore, so when open they present almost no restriction — the conductance is close to that of a straight pipe. That matters directly above a turbo or cryo pump, where a valve that throttles the inlet throws away pumping speed you paid for. The cost is length: the body has to house the plate, so a gate valve is physically deep.

Angle valves turn the flow 90°, which makes them the natural choice where a pump connects to the side of a chamber or where you need to isolate a gauge or a roughing line. They are compact and cheap for their size, and the bellows-sealed versions seal the stem without an elastomer in the vacuum, which is why they dominate on small high-vacuum lines.

Butterfly valves put a disc in the bore and rotate it. The disc never leaves the gas path, so conductance when open is meaningfully lower than a gate valve of the same size — but the body is short and the price is low, and for throttling or for a foreline where you are not chasing the last of the pumping speed, that trade is usually right. A butterfly is also the standard basis for a controlled throttling valve.

Pendulum valves swing the plate in an arc and then press it down, giving full-bore conductance like a gate valve in a much shorter body. That is why they are standard on semiconductor process chambers where vertical space above the turbo is scarce. They cost more and have more moving parts in vacuum.

Then check the three things that decide whether the valve survives: permissible differential pressure and which direction it may be applied (many valves seal in one direction only); the seal material against your process — FKM is the default, EPDM for some solvents, and all-metal (usually copper or a metal seal) where bakeout or ultra-high vacuum rules elastomers out; and the actuation you can actually supply — pneumatic needs clean dry air at the stated pressure, electric needs the right voltage, and manual is only realistic where nobody has to operate it during a cycle.