The vacuum valve has the following characteristics: the pressure is lower than atmospheric pressure, and the pressure drop on the valve flap cannot exceed 1 kg/cm2. The operating temperature of the media depends on the process in which the device is used. The temperature generally does not exceed the range of -70 to +150 °C.
The most basic requirement for such valves is to ensure a high degree of sealing of the joints and compactness of the structure and gasket material.
Vacuum valves can be divided into four groups according to the medium pressure:
1) Low vacuum valve: medium pressure p = 760 ~ 1 mm Hg;
2) Medium vacuum valve: p = 1 × 10 -3 mm Hg.
3) High vacuum valve: p = 1 × 10 -4 ~ 1 × 10-7 mm Hg;
4) Ultra-high vacuum valve: p ≤ 1 × 10-8 mm Hg.
As a closed-circuit valve with a diameter of less than 250 mm, the widely used valve stem is a vacuum bellows shut-off valve for linear motion. Gate valves are subject to greater restrictions, but this is primarily for large diameter paths. Also available are ball plug valves (ball valves), plunger valves and butterfly valves. Plug valves for vacuum valves have not been popularized because the plug valves need to be lubricated with oil so that oil vapor can enter the vacuum system, which is not allowed. Vacuum valves can be used both on-site manual and remote control, as well as on electric, electromagnetic (solenoid), pneumatic and hydraulic controls.
The vacuum valve closure is sealed with a rubber seal or a metal seal. The bellows of the bellows stop valve are made of stainless steel, high-zinc brass JI80, plastic and other materials. Diaphragm seals with small diameters (with a diameter of 10 mm or less) can be sealed with a diaphragm. A spherical plug valve can be used for the low vacuum and the medium vacuum.
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