Grinding shaft phenomenon caused by leakage of
mechanical seal of submersible sewage pump
(1) The mechanical seal failure of small pumps below 715kW often causes grinding shafts. The main positions of the grinding shafts are as follows: the auxiliary sealing ring of the moving ring, the position of the static ring, and a few springs have grinding shafts. mechanical seal
(2) The main reason for shaft grinding: ① BIA type double-end mechanical seal, the back pressure state is a bad working state, particles and impurities in the medium can easily enter the sealing surface, making the seal invalid. ② The main part of the grinding shaft is a rubber bellows, and because the upper sealing surface is in a poorly lubricated state, the friction torque between the dynamic and static rings is greater than the transmission torque between the rubber bellows and the shaft, and relative rotation occurs. ③ The auxiliary seals of the dynamic and static rings are corroded by the weak acid and alkali in the sewage, and the rubber parts are inelastic. Some have rotted and lost their proper functions, resulting in shaft grinding.
(3) In order to solve the above problems, the following measures are now taken: ① Ensure the cleanliness of the lower end cover and oil chamber, and prohibit the assembly of unclean lubricating oil. ② The oil surface line in the machine seal oil chamber should be higher than the sealing surface of the dynamic and static rings. ③Choose mechanical seals with different structures according to different working media. For high-lift pumps, the mechanical seal structure should be redesigned, and for corrosive media, fluororubbers resistant to weak acids and alkalis should be selected. The static ring of the machine seal should be equipped with anti-rotation pins.
Industrial control abstract: The proportion of mechanical seal leakage accounts for more than 50% of all maintenance pumps. 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 movement of the pump rotor is large, the interference between the auxiliary seal and the shaft is large, and the moving ring cannot move flexibly on the shaft. After the pump is overturned and the dynamic and static rings are worn, the compensation displacement cannot be obtained.
Countermeasures: When assembling the mechanical seal, the axial movement of the shaft should be less than 0.1 mm, and the interference between the auxiliary seal and the shaft should be moderate. While ensuring the radial seal, the moving ring can move flexibly on the shaft after assembly ( Press the moving ring against the spring to spring back freely).
(2) Insufficient amount of lubricating oil on the sealing surface causes dry friction or roughening of the sealing end surface.
Countermeasures: The lubricating oil level in the oil chamber should be higher than the sealing surface of the dynamic and static rings.
(3) Periodic vibration of the rotor. Causes are stator misalignment with upper and lower endshields or impeller and shaft imbalance, cavitation or bearing damage (wear), which can shorten seal life and cause leakage.
