Common leakage phenomenon
A. Periodic leakage
(1) The axial movement of the pump rotor is large, and 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 turned over and the moving and static rings are worn, the displacement cannot be compensated. Countermeasures: When assembling the mechanical seal, the axial movement of the shaft should be less than 0.1mm, and the interference between the auxiliary seal and the shaft should be moderate. While ensuring the radial seal, the moving ring is equipped with an all-stainless steel gear pump. Flexible movement on the shaft (press the moving ring to the spring to bounce back freely).
(2) Insufficient lubricant on the sealing surface causes dry friction or roughness on the sealing end surface. Countermeasures: The height of the lubricating oil surface in the oil chamber should be higher than the sealing surface of the dynamic and static rings.
(3) The rotor vibrates periodically. The reason is the misalignment of the stator and the upper and lower end caps or the imbalance of the impeller and the main shaft, cavitation or bearing damage (wear). This situation will shorten the seal life and cause leakage.
B. Shaft grinding caused by leakage of the seal of the small submersible sewage pump
(1) The mechanical seal failure of small pumps below 715kW often produces shaft grinding. The positions of the grinding shaft are mainly as follows: the auxiliary sealing ring of the moving ring, the position of the static ring, and a few springs have the phenomenon of shaft grinding.
↑Click on the pic above to learn 【submersible sewage pump】products, prices, parameters etc.↑
(2) The main reasons for shaft grinding: ①BIA type double end face mechanical seal, the back pressure state is a bad working condition, particles and impurities in the medium can easily enter the sealing surface and cause the seal to fail. ②The main part of the grinding shaft is a rubber bellows, and because the upper sealing surface is in a poor lubrication state, the friction torque between the moving and static rings is greater than the transmission torque between the rubber bellows and the shaft, and relative rotation occurs. ③ The dynamic and static ring auxiliary seals are corroded by the weak acid and weak alkali in the sewage, and the rubber parts have no elasticity. Some have rotted and lost their proper function, resulting in the phenomenon of shaft grinding.
(3) In order to solve the above problems, the following measures are taken: ①Ensure the cleanliness of the lower end cover and oil chamber, and it is forbidden to assemble dirty lubricating oil. ②The oil level line in the oil chamber of the engine seal should be higher than the sealing surface of the static and dynamic rings. ③Choose mechanical seals of different structures according to different media used. For high-lift pumps, the mechanical seal structure should be redesigned, and for corrosive medium rubber, fluorine rubber that is resistant to weak acids and weak bases should be selected. The machine-sealed static ring should be equipped with anti-rotation pins.
C. Leakage due to pressure
(1) Mechanical seal leakage caused by high pressure and pressure waves. When the spring specific pressure and total specific pressure are too large and the pressure in the seal cavity exceeds 3MPa, the specific pressure of the seal end face will be too large, the liquid film will be difficult to form, and the seal end face will be severely worn. , The heat generation increases, causing thermal deformation of the sealing surface. Countermeasures: When assembling the mechanical seal, the spring compression must be carried out in accordance with the regulations. Excessive or too small is not allowed. Measures should be taken for the mechanical seal under high pressure. In order to make the end face force reasonable and minimize deformation, materials with high compressive strength such as cemented carbide and ceramic can be used, and cooling and lubrication measures should be strengthened, and reliable transmission methods such as keys and pins can be selected.
(2) Mechanical seal leakage caused by vacuum operation. During the start and stop of the pump, due to the blockage of the pump inlet and the gas contained in the pumped medium, it may cause negative pressure in the sealed cavity. If there is negative pressure in the sealed cavity, it will Dry friction on the seal end surface will cause air leakage (water) in the built-in mechanical seal. The difference between vacuum seal and positive pressure seal is the difference in the directionality of the sealing object, and the mechanical seal also has its adaptability in a certain direction. Countermeasure: Adopt double end face mechanical seal, which helps to improve lubrication conditions and improve sealing performance.
D. Leakage due to medium
(1) After most of the mechanical seals of submersible sewage pumps are disassembled, the auxiliary seals of the static ring and the moving ring are inelastic, and some have rotted, causing a large amount of leakage of the mechanical seal and even the phenomenon of shaft grinding. Due to the corrosive effect of high temperature, weak acid and weak alkali in the sewage on the static ring and the auxiliary rubber seal of the moving ring, the mechanical leakage is too large. The material of the moving and static ring rubber sealing ring is nitrile-40, which is not resistant to high temperature. It is not resistant to acid and alkali, and it is easy to corrode when the sewage is acid and alkali. Countermeasures: For corrosive media, rubber parts should be fluorine rubber resistant to high temperature, weak acid and weak alkali.
(2) Mechanical seal leakage caused by solid particles and impurities. If solid particles enter the end face of the seal, it will scratch or accelerate the wear of the end face. The accumulation of scale and oil on the surface of the shaft (sleeve) exceeds the wear speed of the friction pair, resulting in The moving ring cannot compensate for the wear displacement, and the operating life of the hard-to-hard friction pair is longer than that of the hard-to-graphite friction pair, because solid particles will be embedded in the sealing surface of the graphite sealing ring. Countermeasures: The mechanical seal of tungsten carbide to tungsten carbide friction pair should be selected in the position where solid particles are easy to enter.
