Chapter 4.1 - Selection Considerations for Vacuum Valves

Abstract

This chapter discusses several factors that are considered when selecting a vacuum valve. Valves can be used to control pressure in a vacuum system. There are two types of control valves—those that regulate the admission of gas, and those that control the pumping or removal of gas from a system. Some control valves do provide shutoff, although it is a misapplication of a control valve to use it for shutoff only. Valves can be opened and closed manually, with a pneumatic cylinder, or with a motor. The type of actuation is independent of the stem seal used. Manual or hand actuation is usually the simplest and the least expensive. Frequently a screw arrangement is used for producing linear motion of the valve stem. Another form of manual actuation sometimes found on smaller valves uses a toggle lever and linkage to the stem. Valves that provide shutoff have either a metal or a polymer seal between the valve plate and the body. Polymers are inexpensive, but may be damaged by the process, have higher permeation, and outgassing rates, can be a source of particulates, and usually are not suitable for ultrahigh vacuum (UHV) pressures. Bakeout temperatures of valves are usually limited by any polymers used—either within the vacuum, or for pneumatic seals of the actuator.