Several Issues to Consider When Designing a Vacuum System

The vacuum system must meet the requirements for vacuum production. In addition to performance-standard vacuum pump equipment and good pipeline flow guidance, it is also necessary to ensure reliable sealing and venting performance of the materials in the system structure. Therefore, during the structural design process, the vacuum system solution reminds you to pay attention to the following issues:

1. Choose standard seamless steel pipes and plates for structural materials to reduce welded structures and improve the airtightness of vacuum components. For system components that require welded structures, select steel with good welding performance.

2. Design the welding structure reasonably to improve the quality of the welding process. Welding is an important procedure in the construction of the vacuum system. The welding structure should avoid gaps where dirt can accumulate in the welds under vacuum. If dirt accumulates or gaps appear, it will not only make cleaning difficult but also become a source of slow venting in the vacuum system. If there are dead spaces in the welds, it will be difficult to locate the leaks.

3. Avoid the appearance of isolation holes (air pockets), or provide vent holes for quick vacuuming. Air pockets can become sources of slow venting, increasing the evacuation time.

4. It is best to electroplate, polish, or oxidize the components and inner walls of the vacuum system to reduce surface venting. Different vacuum environments have different requirements for the roughness of the inner walls. In principle, the components and the inner wall surface of the shell in the vacuum system should be as smooth as possible (generally, the roughness Ra of high vacuum inner walls is 6.3 to 3.2; the roughness Ra of medium vacuum inner walls is about 12.5; ultra-high vacuum inner walls require polishing to achieve a very smooth surface. Additionally, it is important to note that rusty metal surfaces are very detrimental to vacuuming.

5. Flange connections should be welded first and then processed to ensure dimensional and roughness requirements as well as airtightness. Welding can easily cause flange deformation, so currently, domestic practices involve processing the flange after welding, which can meet the requirements for dimensions and roughness while ensuring reliable sealing when connecting two flanges.

6. Vacuum rubber seals working at high temperatures can be protected with a water-cooling structure to prevent damage to components or shorten their lifespan.

7. The walls of vacuum system components and vacuum chamber shells must meet a certain thickness to ensure they have sufficient strength to avoid deformation under internal and external forces (must not deform under 3 atmospheres of pressure). In practical applications, vacuum containers are generally better with a circular structure; while end caps are better with a convex structure.

8. Ensure the dynamic sealing performance of rotating or moving parts entering the vacuum chamber from the outside. In addition to choosing a good sealing structure, the shafts or rods must meet roughness requirements to prevent axial scratches on the shafts and rods, as these scratches can cause gas leaks, reduce the vacuum level of the system, and are not easy to detect.

9. The arrangement of the measurement tube seat position on the vacuum system should follow these principles: a. Do not place the measurement tube in areas with many sealing surfaces. Since no sealing surface can guarantee absolute no leakage, areas with concentrated sealing surfaces are bound to be prone to leaks, and measurement values may be inaccurate. b. The inner wall of the measurement tube must ensure vacuum cleanliness; otherwise, it will cause measurement inaccuracies. c. The measurement tube should be connected as close as possible to the measured area to reduce measurement errors.

10. The water jacket structure on the vacuum chamber shell must ensure that water flows smoothly without obstruction, and there should be no dead water to avoid local overheating. Therefore, the positions of the inlet and outlet pipes should be one above and one below, and a flow separation layer should be set up to guide the water to flow along a certain route.