Vacuum Pump Unit in Electronic Industry Application
Valves of vacuum pump units are used in vacuum devices to separate various parts of the system. According to its working characteristics, it can be divided into pre-vacuum valves and high vacuum pump units. The main difference between them is the diameter of the entrance and exit and the vacuum sealing structure. The diameter of the entrance and exit of the former is generally about 15-20 mm. Vacuum rubber gaskets are usually used to seal the pre-vacuum part, while the diameter of the latter is 65, 100, 150, 180 mm or larger. Metal gaskets (especially valves for ultra-high vacuum part) are commonly used for sealing. Only when the limit vacuum is less than 10-6 brackets, rubber seals are used more frequently. They are widely used in materials, such as brass, steel, stainless steel and other metals. Because of the porous casting, vacuum valves do not need castings. For the main forms of sealing between stem and cover or valve body, there are no more than two kinds of rubber and metal wrinkle pipe. Film (referring to wrinkle film seal made of bronze or nickel in valve with thickness of 0.1-0.15mm, generally its reciprocating stroke is 2-4mm) is less used. Vacuum rubber is generally used for sealing the valve orifice (referring to the sealing of the shut-off valve). Conical disc (made of soft material silver, nickel or brass) and round reciprocating seat (made of quenched steel) are tightly linearly sealed. Because of its poor durability (such as slightly inclined disc to seat, faulty sealing surface, and excessive compaction of disc to squeeze the seat, the valve is no longer tight and needs repair). It is only used in ultra-high vacuum. Oil seals and liquid metal seals are not widely used except for some systems with high vacuum requirements and small duct size.
In designing the vacuum valve, we should pay full attention to its working characteristics, rationally design the structure and put forward the technical conditions. The main requirements are as follows: 1) No leakage should be allowed anywhere in the valve. 2) The vacuum tightness and reliability should be guaranteed when the connection of the valve and the sealing of the valve when it is closed. Sealed parts are best replaceable. 3) The inlet and outlet of the valve and the valve chamber should be as straight as possible, so as to make the air flow less turning, and when the valve is opened, there is enough space for air flow to pass through, with good conductivity. 4) The valve should be switched on and off lightly and conveniently, with extreme position (on, off, deflate... ) The operation sequence and rotation direction should be marked and positioned. 5) All metal parts of the valve (especially the inner surface) should be corrosion-resistant, with low steam pressure and smooth surface. 6) The structure of the valve should be simple and easy to manufacture. Attention should be paid to reducing the weld to a minimum. Use less or avoid structures (such as vacuum welding) that are difficult to process under special processing and factory conditions. Typical structure principle of common vacuum valve. Their operating power includes manual, pneumatic and electric power. The structure of vacuum valve is divided into single valve (including two-way and three-way).