To master the inspection and maintenance 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 (the stationary ring and the moving ring) that are perpendicular to the axis and have smooth and straight surfaces that are in close contact with each other and rotate relatively. It achieves the sealing purpose by generating an appropriate clamping force on the contact surface (end face) of the rotating moving ring and the stationary ring through the pressure of the sealing medium, causing the two end faces to be closely combined and maintaining an extremely thin liquid film between the end faces. This liquid film possesses both dynamic and static pressure of the liquid and serves to lubricate and balance the force. The maintenance process of mechanical seals for water pumps mainly includes the following aspects:

one Cleaning and inspection of mechanical seals

The working principle of mechanical seals requires that there be no impurities inside the mechanical seals. Before assembling the mechanical seal, the dynamic ring, static ring, shaft sleeve and other components should be thoroughly cleaned. Key inspection points

Check if there are any scratches, cracks or other defects on the surfaces of the dynamic and static rings (5 and 6). The presence of these defects can cause severe 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, pressurized water will enter the sealing surfaces of the dynamic and static rings of the assembled mechanical seal, separating the dynamic and static rings and causing the mechanical seal to fail. When necessary, tooling can be made for a hydrostatic test before assembly.

2. Check whether there are any defects affecting the sealing of the dynamic and static ring seats (2). Whether there are any 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 (7) is damaged or deformed, and whether the elasticity coefficient has changed.

4. Check whether the sealing shaft sleeve (8) has any defects such as burrs and grooves.

5. Clean and inspect all sealing rubber rings for any cracks, pores or other defects, and measure whether the diameter of the rubber rings is within the working tolerance range.

6. For mechanical seals with pumping mechanisms, it is also necessary to check whether the screw line of the screw pump has defects such as cracks and broken lines.

two Dimensional verification of mechanical seal assembly technology

The maintenance process of mechanical seals is rather complex. To ensure that the assembled mechanical seals have no leakage, the verification of the technical dimensions of the mechanical seals is indispensable.

Measure the dimensions of the sealing surfaces of the dynamic ring and the static ring (5, 6). 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 friction surface of the hard material should be 1-3mm larger than that of the soft material; otherwise, it is easy for the sharp corners of the end face of the hard material to embed into the end face of the soft material.

2. Check the clearance between the moving ring, the stationary ring (5, 6) and the shaft or the shaft sleeve (8). The inner diameter of the stationary ring is generally 1-2mm larger than the shaft diameter. For the moving ring, to ensure buoyancy, the inner diameter is 0.5-1mm larger than the shaft diameter to compensate for the vibration and deviation of the shaft. However, the clearance should not be too large; otherwise, the sealing ring of the moving ring may get stuck, causing damage to the mechanical seal function.

3. Verification of the tightness of mechanical seals. The mechanical seal clamping force we usually refer to is the end face specific pressure. The end face specific pressure should be appropriate. If it is too large, it will cause the friction surface of the mechanical seal to heat up, accelerate the wear of the end face, and increase the friction power. It's too small and prone to leakage. The end face specific pressure is determined during the design of the mechanical seal. During assembly, we can only determine it by measuring the tightness of the mechanical seal. The common measurement method is to measure the vertical distance from the end face of the installed static ring to the end face of the cover (2), and then measure the vertical distance from the end face of the dynamic ring to the end face of the cover. The difference between the two is the tightness of the mechanical seal.

4. Measure whether the length of the compensation spring (7) has changed.

The change in the performance of the spring will directly affect the end face specific pressure of the mechanical seal. Under normal circumstances, the length of a spring will shorten after long-term operation, and the mechanical seal that compensates the spring on the moving ring will also deform due to centrifugal force.

5. Measure the length of the anti-rotation pin of the static ring and the depth of the pin hole to prevent the pin from being too long and the static ring from not being assembled properly. This situation will damage the mechanical seal.

Three Assembly of mechanical seals

After cleaning, inspection and technical dimension verification, the mechanical seal can be reinstalled. During this process, the following points should be noted:

When assembling, all sealing rings should be coated with soapy water or other lubricants to prevent damage to the rubber rings during the assembly process. Grease is applied between the sealing surfaces of the moving and stationary rings to prevent the sealing surfaces of the moving and stationary rings from wearing out before the water pump is started.

When assembling the floating ring, be extremely careful not to knock over the floating ring spring, as it may affect the floating performance of the floating ring if the spring is knocked over. After the floating ring is assembled, you can gently press it to determine if it has good floating performance.

3. When installing the seal, handle it with care to prevent damage to the seal parts. During installation, clean the seal and the cavity thoroughly.

When tightening the mechanical seal cover, the tightening bolts should be evenly stressed to prevent uneven force from damaging the mechanical seal. For quick-installation mechanical seals, after the overall assembly is completed, do not forget to move the positioning plate radially to a position far from the shaft and fix it.

The mechanical seal of the water pump can be assembled in accordance with the above three steps, which can ensure that the assembled mechanical seal has no leakage or other problems. However, during the maintenance of mechanical seals, it is also necessary to analyze specific problems specifically. This is because the media sealed by mechanical seals are different, such as the temperature of cold water and hot water, whether the sealed medium is corrosive, and the pressure inside the chamber. All these factors will lead to different designs of mechanical seals and different maintenance processes. Therefore, we need to be flexible and adaptable in the maintenance work. Only in this way can the quality of maintenance be guaranteed.

Over the years of mechanical seal maintenance, some experiences have been summarized:

Mechanical seals need to be assembled. Do not forget to clean and inspect them.

First, check the two rings and then the shaft. Do not miss any scratches or cracks.

Finally, take a look at the rubber ring. Make sure the diameter of the air holes is clear.

All dimensions need to be measured, and the gap between the two rings should be adjusted properly.

The tension must be checked. The small spring is the key.

The force on the bolts should be evenly distributed. It is a good habit to handle them gently.