Grinding phenomenon caused by leakage of submersible sewage pump seal

(1) Sealing failure of small pumps below 715kW often results in shaft grinding, which can be mainly located at the auxiliary sealing ring of the dynamic ring, the position of the static ring, and a few springs with shaft grinding. Mechanical seals

(2) The main reason for grinding the shaft: ① BIA type double end mechanical seal, the reverse pressure state is a poor working state, and particles and impurities in the medium can easily enter the sealing surface, causing the seal to fail. ② The main component of the grinding shaft is the rubber bellows, and due to poor lubrication of the upper sealing surface, the friction torque between the dynamic and static rings is greater than the transmitted torque between the rubber bellows and the shaft, resulting in relative rotation The auxiliary seals of the dynamic and static rings have lost their elasticity due to corrosion from weak acids and bases in sewage. Some have rotted and lost their proper function, resulting in the phenomenon of grinding the shaft.

(3) To solve the above problems, the following measures are taken: ① Ensure the cleanliness of the lower end cover and oil chamber, and prohibit the assembly of unclean lubricating oil. ② The oil level line inside the sealed oil chamber should be higher than the sealing surface of the dynamic and static rings Select machine seals with different structures according to different usage media. For high head pumps, the mechanical seal structure should be redesigned, and for corrosive media rubber, weak acid and weak alkali resistant fluororubber should be selected. The static ring of the machine seal should be equipped with anti rotation pins.

Industrial control summary: The proportion of mechanical seal leakage accounts for more than 50% of all repaired pumps, and the operation of mechanical seals directly affects the normal operation of water pumps. The summary and analysis are as follows.

Periodic leakage

(1) The axial displacement of the pump rotor is large, the interference between the auxiliary seal and the shaft is large, and the dynamic ring cannot move flexibly on the shaft. After the pump flips and the dynamic and static rings wear out, no compensation displacement can be obtained.

Countermeasure: When assembling mechanical seals, the axial displacement of the shaft should be less than 0.1mm, and the interference fit between the auxiliary seal and the shaft should be moderate. While ensuring radial sealing, the dynamic ring should be able to move flexibly on the shaft after assembly (by pressing the dynamic ring against the spring and allowing it to bounce back freely).

(2) Insufficient lubricating oil on the sealing surface can cause dry friction or fraying of the sealing end face.

Countermeasure: The height of the lubricating oil level in the oil chamber should be increased to be higher than the sealing surface of the dynamic and static rings.

(3) Periodic vibration of the rotor. The reason is that the stator is not aligned with the upper and lower end covers or the impeller and main shaft are unbalanced, resulting in cavitation or bearing damage (wear), which can shorten the sealing life and cause leakage.