Analysis of common leakage causes of the hottest w

2022-10-21
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Analysis of common leakage causes of water pumps

common leakage phenomenon

the proportion of mechanical seal leakage accounts for more than 50% of all maintenance pumps. The operation of mechanical seal directly affects the normal operation of water pumps, which is summarized and analyzed as follows

1. 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 moving ring cannot move flexibly on the shaft. After the pump is overturned and the dynamic and static rings are worn, the displacement cannot be compensated

countermeasures: when assembling the mechanical seal, the axial displacement 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 movable ring can move flexibly on the shaft after assembly (press the movable ring towards the spring and bounce back freely)

(2) insufficient lubricating oil on the sealing surface causes dry friction or roughening of the sealing face

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 rotor. The reason is that the stator is not aligned with the upper and lower covers, or the impeller and main shaft are unbalanced, cavitation or bearing damage (wear), which will shorten the seal life and produce leakage

countermeasures: the above problems can be corrected according to the maintenance standards

2. Shaft grinding caused by leakage of mechanical seal of small submersible sewage pump

(1) shaft grinding is often caused by the failure of mechanical seal of small pump below 715kw. The main positions of shaft grinding are as follows: the auxiliary sealing ring of moving ring, the position of static ring, and a few springs have shaft grinding

(2) main reasons for shaft grinding:

① BIA double face mechanical seal, the back pressure state is a poor working state, and the particles and impurities in the medium are easy to enter the sealing surface, making the seal invalid

② the main part of the grinding shaft is the rubber bellows, and because the upper sealing surface is in a poor lubrication state, the friction torque between the dynamic and static rings is greater than the transmission torque between the rubber bellows and the shaft, resulting in relative rotation

③ the dynamic and static ring auxiliary seals are corroded by weak acids and alkalis in the qdlp mode of exploring the venture capital market in sewage, and the rubber parts have no elasticity. Some have rotted and lost their functions, resulting in the phenomenon of shaft grinding

(3) in order to solve the above problems, the following measures are taken:

① ensure the cleanliness of the lower cover and oil chamber, and prohibit the assembly of unclean lubricating oil

② the oil level line in the mechanical seal oil chamber shall be higher than the sealing surface of the dynamic and static rings

③ choose mechanical seals with different structures according to different media. For high lift pumps, the mechanical seal structure should be redesigned, and for corrosive medium rubber, fluororubber with weak acid and alkali resistance should be selected. Anti rotation pin shall be added to the static ring of mechanical seal

leakage caused by pressure

in order to provide more perfect products and services for regional customers (1) mechanical seal leakage caused by high pressure and pressure wave. When the spring specific pressure and total specific pressure are designed to be too large and the pressure in the seal cavity exceeds 3Mpa, the specific pressure of the seal face will be too large, the liquid film will be difficult to form, the seal face will be seriously worn, the heat will increase, and the seal face will be thermally deformed

countermeasures: when assembling the mechanical seal, the spring compression must be carried out according to the regulations, and it is not allowed to be too large or too small. Measures should be taken for the mechanical seal under high pressure. In order to make the stress on the end face reasonable and minimize the deformation, materials with high pressure resistance such as cemented carbide and ceramics can be used, and cooling lubrication measures can be strengthened, and * transmission methods, such as keys and pins, can be selected

(2) in the process of starting and stopping the mechanical seal leakage pump caused by vacuum operation, due to the blockage of the pump inlet and the gas contained in the pumping medium, there may be negative pressure in the sealing cavity. If the sealing cavity is negative pressure, it will cause dry friction on the sealing end face, and the built-in mechanical seal will produce air leakage (water). The difference between vacuum seal and positive pressure seal lies in the directional difference of the sealing object, And the mechanical seal also has its adaptability in one direction

countermeasures: adopt double face mechanical seal, which will help improve lubrication conditions and seal performance

leakage caused by media

(1) after the disassembly of the mechanical seals of most submersible sewage pumps, the auxiliary seals of the static ring and the moving ring are inelastic, and some have rotted, resulting in a large number of leakage of the mechanical seals and even the phenomenon of shaft grinding. Due to the corrosive effect of high temperature and weak acid and alkali in sewage on the auxiliary rubber seals of static ring and dynamic ring, the mechanical leakage is too large. The material of dynamic and static ring rubber seals is nitrile-40, which is not resistant to high temperature and acid and alkali. When sewage is acidic and alkaline, it is easy to corrode

countermeasures: for corrosive media, fluororubber with high temperature resistance, weak acid resistance and weak alkali resistance should be selected for rubber parts

(2) mechanical seal leakage caused by solid particle impurities. If solid particles enter the seal end face, the wear of the seal end face will be scratched or accelerated. The accumulation rate of scale and oil on the shaft (sleeve) surface exceeds the wear rate of the friction pair, so that the moving ring cannot compensate for the wear displacement. 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, that is, in the 400 meter race, the speed can be accelerated by half a second into the sealing surface of the graphite sealing ring

countermeasures: the mechanical seal of tungsten carbide on tungsten carbide friction pair should be selected at the position where solid particles are easy to enter

mechanical seal leakage caused by other problems

there are still unreasonable places in the design, selection, installation and so on

(1) the compression amount of the spring must be carried out according to the regulations, and it is not allowed to be too large or too small, with an error of ± 2mm. If the compression amount is too large, the specific pressure of the end face will increase, and the friction heat is too much, which will cause the thermal deformation of the sealing surface and accelerate the wear of the end face. If the compression amount is too small, and the specific pressure of the end face of the dynamic and static rings is insufficient, it cannot be sealed

(2) the end face of the shaft (or shaft sleeve) where the moving ring seal ring is installed and the end face of the gland (or housing) where the stationary ring seal ring is installed should be chamfered and polished to avoid damaging the dynamic and stationary ring seal ring during assembly

the common leakage causes of mechanical seals are summarized above. Mechanical seal itself is a precision component with high requirements, which has high requirements for design, machining and assembly quality. When using controllable seals with mechanical flow direction, various factors of using mechanical seals should be analyzed to make the mechanical seals suitable for the technical requirements of various pumps and the requirements of using media, and have sufficient lubrication conditions, so as to ensure the long-term and reliable operation of the seals

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