Mechanical seal, also known as face seal, has a pair of end faces perpendicular to the axis of rotation. This end face, under the effect of fluid pressure and compensation of the external elasticity of the machine, relies on the cooperation of the auxiliary seal, keeps fit with the other end, and relatively slides, thus preventing Fluid leaks.
First, the common periodic leakage
1. The pump rotor has a large amount of axial turbulence, and there is a large amount of interference between the auxiliary seal and the shaft. The moving ring cannot be flexibly moved on the shaft. When the pump is turned over, the static and dynamic rings wear and no compensation displacement is obtained.
Countermeasures: In the assembly of mechanical seals, the axial axial movement of the shaft should be less than 0.1 mm. The auxiliary seal and the shaft have a moderate amount of interference. While ensuring the radial seal, the ring can be moved flexibly after being assembled. The ring is pressed against the spring to bounce back freely
2. Insufficient amount of lubricant on the sealing surface causes dry friction or roughing
Countermeasures: The height of the lubricant oil in the oil chamber should be higher than the dynamic and static ring sealing surface
3, the rotor is periodically vibrated, because the stator is not aligned with the upper and lower end caps or the impeller and spindle are not balanced, cavitation or bearing damage
Second, leakage due to pressure
1. Leakage of mechanical seal caused by high pressure and pressure waves
Because the specific pressure of the spring and the total specific pressure design are too large, when the pressure in the sealing chamber exceeds 3 Mpa, the sealing end face is over-pressurized, the liquid film is difficult to form, the sealing end face is seriously worn, and the heat generation increases, resulting in thermal deformation of the sealing surface.
Countermeasures: When assembling a mechanical seal, the compression of the spring must be carried out according to the regulations. It must not be too large or too small. Mechanical seals under high pressure conditions should take measures. In order to make the force on the end face reasonable, materials with high compressive strength such as cemented carbide and ceramics can be used, and cooling lubrication measures can be strengthened.
2. Leakage of mechanical seal caused by vacuum operation
In the process of starting and stopping the pump, due to the clogging of the pump inlet and the pumping medium containing gas, there may be negative pressure in the sealing chamber, which may cause dry friction on the sealing surface.
Countermeasures: Double mechanical seals are used to help improve lubrication conditions and seal performance.
Third, due to media leakage
Particles and impurities in the medium enter the sealing surface, causing the seal to fail; the auxiliary seals of the moving and stationary rings lose their proper function due to the weak acid and weak alkali corrosion in the medium.
Countermeasures: ensure the cleanliness of the lower end cap and oil chamber, and prohibit the assembly of unclean lubricants; the oil surface line in the mechanical seal oil chamber should be higher than the sealing surface; use different structural mechanical seals according to different media, such as for corrosive media The rubber parts should be made of fluororubbers that are resistant to high temperatures, weak acids, and weak bases. The mechanical seal of tungsten carbide to tungsten carbide friction pairs should be selected where the solid particles can easily enter.
Fourth, due to other problems caused by mechanical seal leakage
Mechanical seals have irrational places such as design, selection, and installation
Countermeasures: The spring compression error should be between -2 mm -2 mm. If it is too large, the end face pressure is increased. If the frictional heat is too high, the sealing surface will be thermally deformed and accelerate the wear of the end face. If the spring is too small, the ratio of the end face of the static and dynamic rings will be lower. Insufficient pressure, can not be sealed; installation of dynamic seal ring seal gland (or shell) should be chamfered and the end of light, so as not to touch the movement of the assembly, static ring seal.
The above summarizes the leakage causes and countermeasures of mechanical seals. The mechanical seal itself is a demanding precision part. In use, various factors should be analyzed to make the mechanical seal applicable to the technical requirements of various pumps and the use of media requirements, so as to ensure long-term reliable operation.
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