Installation of mechanical seals for multi-stage centrifugal pumps: To master the maintenance and repair of mechanical seals, one must first understand the working principle of mechanical seals. A mechanical seal is a sealing device composed of two sealing elements (a stationary ring and a moving ring) that are perpendicular to the axis, with smooth and straight surfaces that adhere to each other and rotate relative to each other. It relies on the pressure of the sealing medium to generate appropriate clamping force on the contact surface (end face) of the rotating dynamic ring and static ring, so as to tightly bond these two end faces and maintain a very thin liquid film between them to achieve the sealing purpose. This liquid film has both liquid dynamic pressure and static pressure, playing a role in lubricating and balancing forces. The maintenance process of mechanical seals for water pumps mainly includes the following aspects:
1, Dimensional verification of mechanical seal assembly technology for multi-stage centrifugal pumps
The maintenance process of mechanical seals is relatively complex, and to ensure that the assembled mechanical seal has no leakage, it is essential to verify the technical dimensions of the mechanical seal.
1. Measure the dimensions of the sealing surfaces of the dynamic and static rings. This data is used to verify the radial width of the dynamic and static rings. When different friction materials are selected, the radial width of the hard material friction surface should be 1-3mm larger than that of the soft material, otherwise it may cause the sharp edges of the hard material end face to embed into the soft material end face.
2. Check the gap between the dynamic ring, static ring, and shaft or sleeve. The inner diameter of the static ring is generally 1-2mm larger than the shaft diameter. For the dynamic ring, to ensure buoyancy, the inner diameter is 0.5-1mm larger than the shaft diameter to compensate for shaft vibration and deflection. However, the gap should not be too large, otherwise it will cause the dynamic ring seal to get stuck and cause damage to the mechanical seal function.
3. Verification of mechanical seal tightness. The mechanical seal tightening force we usually refer to is the end face pressure ratio. The end face pressure ratio should be appropriate. If it is too large, it will cause the friction surface of the mechanical seal to heat up, accelerate end face wear, and increase friction power; Too small, easy to leak. The end face pressure ratio is determined during the design of mechanical seals, and we can only determine it by measuring the tightness of the mechanical seal during assembly. The usual measurement method involves measuring the vertical distance between the installed static ring end face and the cover end face, and measuring the vertical distance between the moving ring end face and the cover end face. The difference between the two is extremely similar to the tightness of the mechanical seal.
4. Measure whether the length of the compensating spring has changed. The change in spring performance will directly affect the specific pressure of the mechanical seal end face. In general, the length of the spring will shorten after long-term operation, and the mechanical seal of the compensating spring on the moving ring will also deform due to centrifugal force.
5. Measure the length and depth of the anti rotation pin of the static ring to prevent the pin from being too long and the static ring from being assembled in place. This situation can damage the mechanical seal.
2, Assembly of mechanical seals for multi-stage centrifugal pumps
After cleaning, inspection, and technical dimension verification, the mechanical seal can be reinstalled. During this process, the following points should be noted:
1. During assembly, all sealing rings should be coated with lubricants such as soapy water to avoid damage to the rubber rings during the assembly process. Apply lubricating grease between the sealing surfaces of the dynamic and static rings to prevent them from wearing out before the water pump is started.
2. When assembling the floating ring, be careful not to knock over the floating ring spring, so as not to affect the floating performance of the floating ring after the spring is knocked over. After assembling the floating ring, you can gently press the floating ring to determine if it has good floating performance.
3. When installing the seal, it should be handled gently to prevent damage to the seal. The seal and cavity should be cleaned thoroughly during installation.
4. When tightening the mechanical seal cover, the fastening bolts should be evenly stressed to prevent uneven stress from damaging the mechanical seal. After the overall assembly of the quick installation mechanical seal, do not forget to fix the position of the locating plate radially away from the axis.
3, Inspection of mechanical seals for multi-stage centrifugal pumps
The working principle of mechanical seals requires that there be no impurities inside the mechanical seal. Thoroughly clean the moving ring, stationary ring, shaft sleeve and other components before assembling the mechanical seal. Key inspection:
1. Whether there are scratches, cracks, and other defects on the surface of the dynamic and static rings, which can cause serious leakage of the mechanical seal. If conditions permit, special tools can be used to check whether the sealing surface is flat. If the sealing surface is not flat, pressure water will enter the sealing surface of the dynamic and static rings of the assembled mechanical seal, separating the dynamic and static rings and causing the mechanical seal to fail. If necessary, fixtures can be made for hydrostatic testing before assembly.
2. Check for any defects in the dynamic and static ring seats that may affect the sealing. Whether there are defects such as scratches on the mating surface between the dynamic and static ring seat and the dynamic and static ring sealing rubber ring.
3. Check whether the mechanical seal compensation spring is damaged or deformed, and whether the resistance coefficient has changed.
4. Check the sealing shaft sleeve for defects such as burrs and grooves.
5. Clean and inspect all sealing gaskets for defects such as cracks and air holes, and measure the diameter of the gaskets to ensure it is within the tolerance range.
6. Mechanical seals with pumping mechanisms should also be inspected for defects such as cracks and broken wires in the spiral line of the screw pump.
