How to improve the sealing performance of vacuum system of vacuum pump unit mainly lies in strengthening the repair of vacuum system leakage. The factors causing poor vacuum sealing performance are roughly taken four measures.

1. During the overhaul, the clearance of vacuum pump shaft seal is adjusted to 0.35 ~ 0.45mm by rolling adhesive tape. Meanwhile, during the operation of vacuum pump unit, the steam pressure of shaft seal shall be increased as much as possible under the premise of no water entering into the lubricating oil.

2. The structure of the low pressure explosion-proof door is improved. The inner side of the flange is sealed with reinforced graphite gasket, the outer side is provided with asbestos paperboard gasket, and the inner flange is sealed by high and low steps. During the overhaul, the 2mm thick high pressure paperboard diaphragm was replaced. During assembly, hz-1213 oil resistant silicone sealant was applied to each joint surface to ensure the tightness of each joint surface.

3. For the vacuum system below the condenser throat, the leakage point is eliminated by filling water.

4. In order to solve the problem of large void value at the low pressure steam inlet and at the junction of the middle section of the low pressure cylinder and the low pressure cylinder, the upper low pressure cylinder and the middle section of the low pressure cylinder are recombined. In the process of combination, the sealing coating for vertical joint surface was replaced. Red lead powder 20% ～ 25%, reduced iron powder with fineness of 200 mesh was 25% ～ 30%, and 50% fine black lead powder was mixed with TR3 cylinder sealing grease produced by Westinghouse according to the weight ratio, and the coating was also used in the middle section of low pressure cylinder. For the horizontal split surface of the junction between the middle section of low pressure cylinder and low pressure cylinder, the coating with thickness of 0.50 ～ 1.0 mm should be applied first The exhaust cylinder is sealed with loctite 596 sealant.