Analysis of leakage phenomenon of mechanical seals used in submersible pumps and its countermeasure


Axis Grinding Phenomenon Caused by Seal Leakage of Submersible Sewage Pump

(1) The failure of small pump seals below 715 kW often results in grinding shaft. The grinding shaft locations are mainly as follows: the auxiliary seal ring of the moving ring, the static ring position, and a few springs have the phenomenon of grinding shaft. Mechanical seals.

(2) The main reasons for grinding shaft are as follows: (1) BIA double-end mechanical seal, the back pressure state is a bad working state, the particles and impurities in the medium can easily enter the seal surface, which makes the seal invalid. (2) Rubber bellows are the main parts of the grinding shaft, and the friction moment between the dynamic and static rings is greater than the transfer torque between the rubber bellows and the shaft due to the poor lubrication of the upper seal surface. (3) Because of the corrosion of weak acid and alkali in sewage, the rubber parts have no elasticity. Some have decayed and lost their proper functions, resulting in the phenomenon of grinding the shaft.

(3) In order to solve the above problems, the following measures are taken: (1) To ensure the cleanliness of the lower cover and oil chamber, and to prohibit the assembly of unclean lubricants. (2) The oil surface of the oil chamber should be higher than that of the dynamic and static ring. 3. Seals with different structures are selected according to different media. The sealing structure of high lift pump should be redesigned, and the fluorine rubber with weak acid and alkali resistance should be selected for the rubber with corrosive medium. The static ring of machine seal should be prevented from being resold.

Industrial control abstract: The leakage rate of mechanical seal accounts for more than 50% of all maintenance pumps. The operation of mechanical seal directly affects the normal operation of 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 can not move flexibly on the shaft. When the pump is turned over and the dynamic and static rings are worn out, the displacement can not be compensated.

Countermeasure: When assembling mechanical seals, the axial displacement of the shaft should be less than 0.1mm, the interference between the auxiliary seal and the shaft should be moderate, while ensuring the radial seal, the movable ring can move flexibly on the shaft after assembling (the pressure of the movable ring can bounce back freely from the spring).

(2) Insufficient lubricating oil on the sealing surface causes dry friction or grooming of the sealing face.

Countermeasure: The height of lubricating oil surface in oil chamber should be higher than that of dynamic and static ring sealing surface.

(3) Periodic vibration of the rotor. The reason is that the stator is not aligned with the upper and lower end caps or the impeller and spindle are not balanced, cavitation or bearing damage (wear), which will shorten the sealing life and cause leakage.