Preventing Leakage of Mechanical Seal of Leakage Pump and Countermeasures
The mechanical seal, also known as the end seal, has a pair of end faces perpendicular to the axis of rotation. The end face relies on the cooperation of the auxiliary seal under the action of fluid pressure and compensating for the mechanical external elastic force, and is kept in close contact with the other end and relatively slid, thereby preventing Fluid leaks.
First, common 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. When the pump is turned over, the moving and stationary rings wear and no compensation displacement is obtained.
Countermeasure: When assembling the mechanical seal, the axial yaw of the shaft should be less than 0.1 mm, and the interference between the auxiliary seal and the shaft is moderate. While ensuring the radial seal, the moving ring can be flexibly moved on the shaft after assembly. The moving ring pressure spring can freely bounce back)
2. Insufficient amount of lubricating oil on the sealing surface causes dry friction or napped sealing end face
Countermeasure: the oil level of the lubricating oil in the oil chamber should be higher than the dynamic and static ring sealing surface.
3. The rotor periodically vibrates because the stator is not centered with the upper and lower end caps or the impeller and the main shaft are unbalanced, cavitation or bearing damage
Second, leakage due to pressure
1. Mechanical seal leakage caused by high pressure and pressure waves
Since the spring specific pressure and the total specific pressure design are too large, when the pressure in the sealed cavity exceeds 3Mpa, the sealing end face is more than the pressure, the liquid film is difficult to form, the sealing end face is seriously worn, and the heat generation is increased, resulting in thermal deformation of the sealing surface.
Countermeasure: When assembling the mechanical seal, the compression of the spring must be carried out according to the regulations, and it is not allowed to be too large or too small. Mechanical seals under high pressure conditions should be taken. In order to make the end face force reasonable, materials with high compressive strength such as cemented carbide and ceramics can be used, and lubrication measures for cooling are strengthened.
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 pumping medium, it may cause negative pressure in the sealing chamber, which may cause dry friction on the sealing surface.
Countermeasure: Double mechanical seals are used to help improve lubrication and improve sealing performance. Third, due to leakage caused by the medium
The particles and impurities in the medium enter the sealing surface, which makes the seal fail. The dynamic and static ring auxiliary seals lose their proper function due to the weak acid and weak alkali corrosion in the medium.
Countermeasures: to ensure the cleanliness of the lower end cover and the oil chamber, it is forbidden to assemble the uncleaned lubricating oil; the oil surface line in the mechanical seal oil chamber should be higher than the sealing surface; mechanical seals with different structures are selected according to different media, such as corrosive media The rubber parts should be made of high temperature resistant, weak acid resistant, weak alkali fluororubber, and the mechanical seal of tungsten carbide to tungsten carbide friction pair is selected at the position where the solid particles are easy to enter.
4. Mechanical seal leakage due to other problems
Mechanical seals are unreasonable in design, selection, installation, etc.
Countermeasure: The error of spring compression should be between -2 mm and 2 mm. If it is too large, the end face pressure will be increased. The friction heat is too much, which will easily cause thermal deformation of the sealing surface and accelerate the wear of the end face. Insufficient pressure, can not be sealed; the end surface of the sealing gland (or housing) of the moving ring sealing ring should be chamfered and polished to avoid damage to the moving and static ring seals during assembly.
The above summarizes the common causes of leakage and countermeasures for mechanical seals. Mechanical seals themselves are a demanding precision part. When in use, various factors should be analyzed to make the mechanical seal suitable for the technical requirements and medium requirements of various pumps, so as to ensure long-term reliable operation.
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First, common 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. When the pump is turned over, the moving and stationary rings wear and no compensation displacement is obtained.
Countermeasure: When assembling the mechanical seal, the axial yaw of the shaft should be less than 0.1 mm, and the interference between the auxiliary seal and the shaft is moderate. While ensuring the radial seal, the moving ring can be flexibly moved on the shaft after assembly. The moving ring pressure spring can freely bounce back)
2. Insufficient amount of lubricating oil on the sealing surface causes dry friction or napped sealing end face
Countermeasure: the oil level of the lubricating oil in the oil chamber should be higher than the dynamic and static ring sealing surface.
3. The rotor periodically vibrates because the stator is not centered with the upper and lower end caps or the impeller and the main shaft are unbalanced, cavitation or bearing damage
Second, leakage due to pressure
1. Mechanical seal leakage caused by high pressure and pressure waves
Since the spring specific pressure and the total specific pressure design are too large, when the pressure in the sealed cavity exceeds 3Mpa, the sealing end face is more than the pressure, the liquid film is difficult to form, the sealing end face is seriously worn, and the heat generation is increased, resulting in thermal deformation of the sealing surface.
Countermeasure: When assembling the mechanical seal, the compression of the spring must be carried out according to the regulations, and it is not allowed to be too large or too small. Mechanical seals under high pressure conditions should be taken. In order to make the end face force reasonable, materials with high compressive strength such as cemented carbide and ceramics can be used, and lubrication measures for cooling are strengthened.
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 pumping medium, it may cause negative pressure in the sealing chamber, which may cause dry friction on the sealing surface.
Countermeasure: Double mechanical seals are used to help improve lubrication and improve sealing performance. Third, due to leakage caused by the medium
The particles and impurities in the medium enter the sealing surface, which makes the seal fail. The dynamic and static ring auxiliary seals lose their proper function due to the weak acid and weak alkali corrosion in the medium.
Countermeasures: to ensure the cleanliness of the lower end cover and the oil chamber, it is forbidden to assemble the uncleaned lubricating oil; the oil surface line in the mechanical seal oil chamber should be higher than the sealing surface; mechanical seals with different structures are selected according to different media, such as corrosive media The rubber parts should be made of high temperature resistant, weak acid resistant, weak alkali fluororubber, and the mechanical seal of tungsten carbide to tungsten carbide friction pair is selected at the position where the solid particles are easy to enter.
4. Mechanical seal leakage due to other problems
Mechanical seals are unreasonable in design, selection, installation, etc.
Countermeasure: The error of spring compression should be between -2 mm and 2 mm. If it is too large, the end face pressure will be increased. The friction heat is too much, which will easily cause thermal deformation of the sealing surface and accelerate the wear of the end face. Insufficient pressure, can not be sealed; the end surface of the sealing gland (or housing) of the moving ring sealing ring should be chamfered and polished to avoid damage to the moving and static ring seals during assembly.
The above summarizes the common causes of leakage and countermeasures for mechanical seals. Mechanical seals themselves are a demanding precision part. When in use, various factors should be analyzed to make the mechanical seal suitable for the technical requirements and medium requirements of various pumps, so as to ensure long-term reliable operation.
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