Vacuum valves are components used to adjust airflow, cut off or connect vacuum pipelines in vacuum systems. The following are its design principles and selection considerations:
I. Design principles
Sealing design: It is key to ensure that the valve has good sealing in a vacuum environment. Use special sealing structures and materials, such as metal sealing surfaces, rubber sealing rings, etc., to prevent external air or other gases from entering the vacuum system and affecting the vacuum degree. For example, high vacuum valves often use knife-edge sealing structures, and achieve high air tightness through the close fit of metal knife edges and sealing pads.
Material selection: Select appropriate materials according to the working requirements and environment of the vacuum system. The material should have low outgassing rate, good mechanical properties and corrosion resistance. Commonly used materials include stainless steel, aluminum alloy, copper, etc. For ultra-high vacuum systems, the outgassing characteristics of the material must also be considered to reduce the release of gas in the system and affect the vacuum degree.
Structural design: The structure of the valve should be simple and compact, easy to install and operate. At the same time, the force of the valve in a vacuum environment should be considered to ensure the strength and stability of the structure. For example, the bellows sealing structure can effectively isolate the inside of the valve from the external environment, while allowing the valve stem to move within a certain range to ensure the normal opening and closing of the valve.
Conductance design: According to the flow requirements of the vacuum system, the conductance of the valve is reasonably designed. The conductance directly affects the ability of gas to pass through the valve. Generally, the conductance is improved by optimizing the valve diameter, internal flow channel shape, etc. to meet the system's pumping speed and flow requirements.
2. Selection considerations
Vacuum degree requirements: Select a suitable valve according to the vacuum degree required by the vacuum system. Different types of vacuum valves are suitable for different vacuum ranges, such as low vacuum valves for vacuum degrees of 10^5 - 10^-1 Pa, high vacuum valves for vacuum degrees of 10^-1 - 10^-7 Pa, and ultra-high vacuum valves for ultra-high vacuum environments below 10^-7 Pa.
Working pressure: In addition to considering the vacuum degree, it is also necessary to pay attention to the pressure that the valve may withstand during operation. Including the maximum working pressure of the system and possible pressure fluctuations, ensuring that the valve can work safely and reliably within the specified pressure range, avoiding valve damage or sealing failure due to excessive pressure.
Diameter selection: Select a valve with a suitable diameter according to the pipe diameter and gas flow requirements of the vacuum system. A diameter that is too small will limit the gas flow, affecting the system's pumping speed and work efficiency; a diameter that is too large may increase the valve cost and may be difficult to install and space layout.
Drive mode: There are many drive modes for vacuum valves, including manual, pneumatic, and electric. Manual drive is suitable for occasions where operation is not frequent and control accuracy is not required; pneumatic drive has the advantages of fast response speed and large operating force, and is suitable for valves that need to be opened and closed quickly; electric drive can achieve remote control and precise position adjustment, and is suitable for vacuum systems with a high degree of automation.
Compatibility: Ensure that the selected valve has good compatibility with other components in the vacuum system, such as vacuum pumps, vacuum pipes, vacuum gauges, etc. Including connection methods, material compatibility, etc., to ensure the normal operation of the entire vacuum system. For example, the connection methods must match. Common ones include flange connection, quick-release connection, etc. The appropriate connection form should be selected according to the specific requirements of the system to ensure that the connection is tight and leak-proof.