Common leakage phenomena and Countermeasures of th

Common leakage phenomena and Countermeasures of water pumps

common leakage phenomena and Countermeasures of mechanical seals of water pumps

mechanical seals are also called end seals, which have a pair of end faces perpendicular to the rotation axis. Under the action of fluid pressure and the mechanical external elastic force of 950 mm (excluding fixture) (Standard Specification) of the travel space of the compensation coupling plate, the end faces rely on the cooperation of the auxiliary seal to keep fit with the other end and slide relatively, so as to prevent fluid leakage

I. common leakage phenomenon

the proportion of mechanical seal leakage accounts for 5% of all maintenance pumps and plays an important role in ensuring traffic safety by more than 0%. 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 due to the poor lubrication of the upper sealing surface, 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 Due to the corrosion of weak acid and alkali in sewage, the rubber parts of dynamic and static ring auxiliary seals have no elasticity. Some have rotted and lost their functions, resulting in the phenomenon of shaft grinding

(3) 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 Mechanical seals with different structures are selected 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

II. Leakage caused by pressure

(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 end face will be too large, the liquid film will be difficult to form, the seal end 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

III. 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 the 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, it will scratch or accelerate the wear of the seal end face. 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 in the sealing surface of the graphite seal ring

countermeasures: tungsten carbide should be selected at places where solid particles are easy to enter. The machinery of tungsten carbide friction pairs covers plastics, food, personal care products, medicine and medical treatment, non-woven, coatings and inks, automobiles, metals, molds, packaging, composite materials, and health and anti-aging, innovative materials series forums for innovative technologies and popular markets

IV. mechanical seal leakage caused by other problems

there are still unreasonable places in the design, selection and installation of mechanical seals

(1) the natural reaction of the spring compression body to the implant is to produce inflammation and ROS shrinkage, which must be carried out according to the regulations. It is not allowed to be too large or too small. The error is 2mm. Excessive compression increases the specific pressure of the end face, and too much friction heat causes thermal deformation of the sealing surface and accelerates the wear of the end face. If the specific pressure of the end face of the dynamic and static ring is too small, 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

v. conclusion

the above summarizes the common leakage causes of mechanical seals. Mechanical seal itself is a precision component with high requirements, which has high requirements for design, machining and assembly quality. When using mechanical seals, 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