Mechanical seal is the main reason for the leakage of water pump, but mechanical seal itself is a high precision part, which has high requirement for design, machining and assembly quality. In the use of mechanical seals, the use of mechanical seal should be analyzed various factors, that is suitable for various pump mechanical seal technology demands and use medium and has good lubrication condition, which ensures that the seal reliably for a long time.
Mechanical seal which is also called end face seal, it has a pair of perpendicular to the axis of the rotating end face, the face in the fluid pressure and compensation under the action of mechanical stretch, rely on the auxiliary seal fit and the other end to keep fit, and the relative sliding, thus preventing fluid leakage.
1. Common leakage phenomenon.
The proportion of mechanical seal leakage is more than 50% of the total maintenance pump, and the operation of mechanical seal directly affects the normal operation of the pump. The summary analysis is as follows.
1. Periodic leakage
(1) the shaft of the pump rotor has a large momentum, and the auxiliary seal and shaft are too large. The moving ring cannot be moved flexibly on the shaft. When the pump is turned over, and the ring is worn, the displacement is not compensated.
Countermeasures: in the assembly of mechanical seal, shaft axial momentum should be less than 0.1 mm, auxiliary seal and shaft interference quantity should be moderate, while guarantee the radial sealing, can guarantee on the shaft collar is assembled flexible mobile (press ring to spring can free to bounce back.
(2) insufficient lubricating oil of the sealing surface to cause dry friction or the end face of the pull hair seal.
Countermeasures: the oil level of the oil chamber should be higher than the moving and static ring sealing surface.
(3) periodic vibration of rotor. The reason is that the stator and upper, lower end cover are not in the middle or impeller and the main shaft imbalance, cavitation or bearing damage (wear), this situation will shorten the sealing life and produce leakage.
Countermeasures: the above problems can be corrected according to the maintenance standard.
2. The grinding shaft phenomenon caused by leakage of small submersible pump machine.
(1) the sealing failure of the small pump under 715kW often produces the grinding shaft, and the grinding shaft position is mainly composed of the following: the moving ring auxiliary seal ring, the static ring position and the few springs have the grinding shaft phenomenon.
(2) the main reason of grinding shaft: the double end face mechanical seal of the BIA, the anti-pressure state is the poor working state, the particles and impurities in the medium can easily enter the sealing surface, so that the seal fails. Of the grinding shaft (2) the main thing for the rubber bellows, and is due to the upper seal face in bad lubrication condition, the friction torque between dynamic and static ring is greater than the rubber bellows and shaft transmission torque, between relative rotation. The rubber parts are inelastic because of the corrosion of weak acid and weak base in sewage. Some have decomposed, lost due function, produced the phenomenon of grinding shaft.
(3) in order to solve the above problems, the following measures are adopted: to ensure the cleanliness of the end cap and oil chamber, and to prohibit the assembly of unclean lubricating oil. The oil surface of the oil chamber in the sealing chamber shall be higher than that of the static ring sealing surface. According to different use media, different structures are selected for sealing. For high lift pump, the structure of the machine seal should be redesigned, and the rubber of the corrosive medium should be used to resist the weak acid and the weak base. Machine seal ring should be added to prevent resale.
2. Leakage due to pressure.
(1) high pressure and the pressure wave caused by the mechanical seal leakage due to the large spring than pressure and total pressure design and seal cavity pressure exceeds 3 mpa, can make the seal face specific pressure is too large, difficult to form, liquid membrane seal face serious wear and tear, calorific value increase, sealing surface caused by the thermal deformation.
Countermeasures: when the assembly machine is sealed, the spring compression amount must be carried out according to the regulation, and no large or too small phenomenon is allowed. The mechanical seal under high pressure should take measures. For the transverse force is reasonable, minimize deformation, can use hard alloy, high crushing strength of the material such as ceramic, and strengthen the lubrication cooling measures to choose can * mode of transmission, such as keys, pins, etc.
(2) vacuum pump mechanical seal leakage caused by the operation in the process of starting, stopping, due to the pump inlet blockage, pumping medium containing gas, is likely to cause a negative pressure seal cavity, seal cavity if negative pressure, the dry friction causes the seals, built-in type mechanical seal will produce (water) of leak phenomenon, vacuum seal and the difference of positive pressure seal seal directional difference of object, and the adaptability of mechanical seal has a certain direction.
Countermeasure: the double end face mechanical seal is used to improve the lubrication condition and improve the sealing performance.
3. Leakage caused by media.
(1) the auxiliary seals of the static ring and the moving ring are inelastic, and some have been decomposed, resulting in a large number of leakage and even grinding of the shaft. Due to the high temperature, the weak acid in the sewage, the weak base to the static ring and the action ring auxiliary rubber seals the corrosion action, caused the mechanical leakage to be too large, the movement, the static ring rubber sealing ring material is butyronitrile — 40, not withstanding high temperature, acid and alkali resistance, when the sewage is acidic and alkaline, easy to corrode.
Countermeasures: for the corrosive medium, the rubber should be used for high temperature, weak acid, weak alkali fluorine rubber.
(2) solid impurities caused by leakage of mechanical seal if solid particles into the seal face, will be cut or speed up the seals of wear and tear, scale and the oil accumulation on the surface of the shaft (set), at a faster rate than wear rate of friction pair, the ring can't compensate displacement of abrasion, hard to hard friction pair work longer than hard to graphite friction pair, because of the solid particles are embedded graphite sealing ring sealing surface.
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. Stainless steel self-priming pump.
Leakage of mechanical seals caused by other problems.
In mechanical seal, there are some unreasonable places such as design, selection and installation.
(1) the spring compression must be carried out in accordance with the regulations, and it is not allowed to have too large or too small phenomena, and the error ± 2mm, too much compression increases the end surface ratio pressure, the friction heat is too much, resulting in the heat deformation of the sealing surface and the acceleration of the end face wear, the compression of the small static ring end face is less than the pressure, then cannot be sealed.
(2) the end face of the shaft (or shaft sleeve) of the ring sealing ring and the sealing gland (or shell) of the ring seal ring shall be chamfered and trimmed to avoid the damage of the ring sealing ring during assembly.
5. Conclusion.
The above summarized the mechanical seal more common leakage reasons. Mechanical seal itself is a kind of high precision parts, which has high requirements for design, machining and assembly quality. In the use of mechanical seals, the use of mechanical seal should be analyzed various factors, that is suitable for various pump mechanical seal technology demands and use medium and has good lubrication condition, which ensures that the seal reliably for a long time.
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