Mechanical seal is the main reason for pump leakage, but the mechanical seal itself is a more demanding precision parts, design, machining, assembly quality has high requirements. In the use of mechanical seals, mechanical seals should be analyzed using a variety of factors that make the mechanical seal suitable for a variety of pump technical requirements and the use of media requirements and adequate lubrication conditions, so as to ensure the long-term sealing operation. Fabric Reinforced Concrete Hose Fabric Reinforced Concrete Hose,Fabric Concrete Hose,Mud Concrete Pumping Hose,Rubber Hose For Concrete Pump Hebei Huayu Special Rubber Co.,Ltd , https://www.api7khose.com
Mechanical seal also known as the end seal, which has a pair of perpendicular to the axis of rotation of the end surface, the end of the fluid pressure and compensate mechanical external elastic force, depending on the auxiliary seal with the other end to maintain fit and slide relative to prevent fluid leakage.
I. Common leakage of pipeline centrifugal pump leakage of mechanical seals accounted for more than 50% of the total maintenance of the mechanical seal of a direct impact on the normal operation of the pump, are summarized as follows.
1. Periodic leakage (1) pump rotor axial play large, auxiliary seal and shaft interference large, flexible ring can not move on the axis of flexibility. In the pump flip, moving, static ring wear, not to compensate for displacement.
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 radial sealing, the moving ring can be flexibly moved on the shaft after assembly The ring pressing the spring can be free to bounce back).
(2) insufficient lubricant on the sealing surface causes dry friction or nap sealing of the end surface.
Countermeasures: oil chamber cavity lubricating oil height should be added to the moving, stationary ring sealing surface.
(3) Rotor periodic vibration. The reason is the misalignment between the stator and the upper and lower end caps or imbalance between the impeller and the main shaft, cavitation or bearing damage (wear), which can shorten the seal life and create leakage.
Countermeasures: According to the maintenance standards to correct the above problems.
2. Small submersible sewage pump seal leakage caused by grinding shaft phenomenon 715kW following small pump seal failure often produce grinding shaft, grinding shaft position mainly in the following: moving ring auxiliary seal ring, the ring position, a few spring Grinding axis phenomenon.
The main reason for grinding shaft: â‘ BIA double mechanical seal, the back pressure state is a bad working condition, the media particles, impurities can easily enter the sealing surface, so that the seal failure. The main parts of the grinding shaft are rubber bellows, and because the upper sealing surface is in a poor lubrication state, the friction torque between the static and the stationary rings is larger than the transmission torque between the rubber bellows and the shaft, and relative rotation occurs. â‘¢ moving, static seal auxiliary seal due to the weak acid in the sewage, weak alkali corrosion, rubber parts have been inelastic. Some have been decayed, lost their due function, resulting in the phenomenon of grinding shaft.
3. Pipeline centrifugal pump To solve the above problems, the following measures are taken: â‘ to ensure the bottom cover, oil chamber cleanliness, prohibited the assembly of unclean lubricants. â‘¡ machine seal oil chamber cavity line should be higher than the static and dynamic ring sealing surface. â‘¢ According to different media use different structure of the machine seal. The high-lift pump should be redesigned machine seal structure, corrosive medium rubber should be resistant to weak acid, weak base of fluorine rubber. Machine seal ring should be added to prevent pin.
Pipeline centrifugal pump leakage due to pressure (1) high pressure and pressure wave caused by the mechanical seal leakage, due to the spring than the pressure and the total pressure design is too large and the pressure inside the sealed chamber exceeds 3MPa, the seal will face the pressure Too large, difficult to form liquid film, seal face serious wear and tear, increased heat, resulting in sealing surface thermal deformation.
Countermeasures: In the assembly machine seal, the amount of spring compression must be carried out according to regulations, not allowed to have too large or too small, under high pressure mechanical seal should take measures. In order to make the end face force reasonable and minimize the deformation, we can adopt materials with high compressive strength such as cemented carbide and ceramics, and strengthen the cooling lubrication measures.
(2) Leakage of mechanical seal caused by operation in vacuum state. During the start-up and shutdown of the pump, due to the blockage of the inlet of the pump and the gas contained in the pumping medium, negative pressure may occur in the sealed chamber, negative pressure in the sealed chamber, Will cause the sealing surface dry friction, built-in mechanical seal will have leakage (water) phenomenon, the vacuum seal and positive pressure seal is different in the direction of the object to be sealed, and the mechanical seal also has its own direction of adaptability.
Countermeasures: The use of double-sided mechanical seal, which will help improve the lubrication conditions, improve the sealing performance.
Pipeline centrifugal pump due to leakage caused by the media (1) Most of the submersible sewage pump mechanical seal dismantling, stationary ring and moving ring auxiliary seal inelastic, and some have been decay, resulting in a large number of machine seal leakage There are even grinding shaft phenomenon. Due to the high temperature, the weak acid and weak base in the sewage corrode the static ring and moving ring auxiliary rubber seal, resulting in excessive mechanical leakage. The material of static and dynamic ring rubber sealing ring is nitrile-40, Acid and alkali, when the water is acidic alkaline easily corroded.
Countermeasures: corrosive media, rubber parts should be used high temperature, weak acid, weak base of fluorine rubber.
(2) Mechanical Seal Leakage Caused by Solid Particle Impurities If solid particles enter the seal face, it will scratch or speed up the wear on the seal face. The accumulation of scale and grease on the shaft (sleeve) surface exceeds the wear rate of the friction pair, causing The moving ring can not compensate for the wear displacement. The working life of the hard-to-hard friction pair is longer than that of the hard-to-graphite friction pair because the solid particles are embedded in the sealing surface of the graphite sealing ring.
Countermeasures: easy access to solid particles in place should be used tungsten carbide pairs of mechanical friction of the mechanical seal.
Fourth, due to other problems caused by the mechanical seal leakage Mechanical seal also exists in the design, selection, installation, etc. not reasonable place.
(1) The amount of compression spring must be carried out according to regulations, not allowed to have too large or too small, the error ± 2mm, excessive compression to increase the end pressure, friction heat too much, resulting in sealing surface thermal deformation and accelerated wear on the end , The amount of compression is too small static and dynamic pressure than the end face of the ring, you can not seal.
(2) The end surface of the shaft (or sleeve) on which the moving ring seal is installed and the seal gland (or casing) on ​​which the stationary ring seal is installed should be chamfered and smoothed to avoid bruising the static and dynamic ring seal during assembly.
V. Conclusion The above summary of the mechanical seal more common causes of leakage. Mechanical seal itself is a high precision parts, the design, machining, assembly quality has high requirements. In the use of mechanical seals, the mechanical seal should be used to analyze the various factors that make the mechanical seal suitable for a variety of pump technical requirements and the use of media requirements and adequate lubrication conditions, so as to ensure the long-term reliable seal operation.