Vacuum valves are used when a vacuum must be maintained in a closed system. Vacuum valves are used to control gas flow into a chamber, isolate, vent, provide relief or control conductance. Gate, inline and angle valves are the most common types of vacuum valves for high vacuum applications. Additional valve types include ball, butterfly, conductance controllers, diaphragm, gas control or leak valve, relief valve, and straight through. Gate valves (also known as knife valves or slide valves) are linear motion valves in which a flat closure element slides into the flow stream to provide shut-off. In-line valves have their inlet port positioned at a parallel to the outlet port, but not necessarily axial with the inlet port. Angle valves have their inlet port positioned at a right angle to the outlet port. Ball valves are quarter-turn, straight through flow valves that have a round closure element with matching rounded seats that permit uniform sealing stress. Butterfly valves are quick opening valves that consist of a metal circular disc or vane with its pivot axes at right angles to the direction of flow in the pipe, which when rotated on a shaft, seals against seats in the valve body. Conductance controllers alter the conductance through the vacuum system by modifying the mean free path that the gas molecules must take. Diaphragm valves use a flexible diaphragm to separate the flow stream from the closure element. Gas metering, throttling or leak valves control the flow of gas into chamber or process vessel. Vacuum or pressure relief valves protect chambers or components form excesses in vacuum or pressure that would otherwise deform or damage the component. Straight through valves have their inlet port positioned at a parallel to the outlet port as well as axial with the inlet port. 

Common specifications for vacuum valves include port size or outer diameter, vacuum or pressure range, and operating or bake-out temperature.  The vacuum or pressure range can be rough or low (< 760, > 1 torr), medium (< 1, >10^-3 torr), high vacuum (< 10^-3, >10^-8 torr), ultra-high vacuum (< 10^-8 torr), and elevated pressures (> 760 torr). The maximum operating or bake-out temperature that the fitting, flange or vacuum component can be exposed to is important to consider.  Flange or seal types for vacuum valves include none, metal seal, elastomeric seal or o-rings, ISO, ANSI ASA, NPT female, NPT male, Conflat, Del-Seal, Pyraflat, Tri-Seal, and VCR or VCO.  Port flange or ISO nominal size refers to the nominal bore size.  Choices range from NW 10 to NW 1000.  Valve seat seal type choices include none, metal seals, and elastomeric seals or o-rings.  An actuator or steam shaft on the valve the bonnet that contains or protect the valve stem or a actuator preventing contamination.

Valve actuation choices for vacuum valves include none or manual, solenoid electric, piezoelectric actuator electric, motorized electric, pneumatic, and electro-pneumatic.  Common features include heater jacket, high conductance, integral window, multi-stage, position indicator, and roughing points.  Fail-safe mechanisms for vacuum valves include spring-to-close or normally closed, and spring-to-open or normally open.