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 are in contact with 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.

1. Cleaning and inspection of mechanical seals

1) 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.

2) Check 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.

3) Check for any defects in the dynamic and static ring seats that may affect the sealing. Whether there are defects on the mating surface between the dynamic and static ring seat and the dynamic and static ring sealing ring.

4) Check whether the mechanical seal compensation spring is damaged or deformed, and whether the resistance coefficient has changed.

5) Check the sealing shaft sleeve for defects such as burrs and grooves.

6) 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.

7) 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.

2. Dimensional verification of mechanical seal assembly technology

1) Measure the size of the sealing surface 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 and static rings and the shaft or shaft 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 ring 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 is to measure the vertical distance from the installed static ring end face to the cover end face, and then measure the vertical distance from the dynamic ring end face to the cover end face. The difference between the two is the tightening force of the mechanical seal.

4) Measure whether the length of the compensating spring has changed. Changes 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.

3. Grinding of the end faces of the moving and stationary rings

1) After disassembling the moving ring, it is ground and processed by rough grinding first, followed by fine grinding. If conditions permit, it can be polished.

2) When rough grinding, use abrasive with a particle size of 80-160 # to first remove the machining marks. Then, 160 # or higher abrasives can be used for precision grinding to achieve the design requirements for smoothness. Hard alloy or ceramic dynamic rings need to be polished with a polishing machine after precision grinding. The force of the polishing machine can be selected from M28 to M5 boron carbide. Polish to achieve a mirror finish. Ceramic rings can be finely ground with M5 agate powder and polished with chromium oxide.

3) The static ring filled with graphite and polytetrafluoroethylene can be finely ground with kerosene, gasoline, or water due to its soft material, without the need for grinding agents. During the running in process, it can also be self-developed, so the requirement for smoothness is not too high.

4) The grinding method can be carried out on a grinder if there is one, and on flat glass if there is no grinder, a manual grinding method with an 8-shaped shape can be used.

4. Shaft sleeve inspection

1) After disassembling the shaft sleeve for maintenance, check for rust and wear. If the rust or wear is relatively minor, use fine sandpaper to polish it before use. If the rust or wear is severe, use electroplating after processing or replace the shaft sleeve with a new one.

5. Sealing ring

1) After a period of use, the sealing ring often loses its elasticity or ages, and generally needs to be replaced with a new ring.

6. Spring

1) If the spring is not severely corroded and can maintain its original elasticity, it does not need to be replaced. If the corrosion is severe or the elasticity decreases significantly, a new spring needs to be replaced.

2) For mechanical seals with assembly boxes, the boxes should be cleaned thoroughly and the grooves checked for wear or deformation for calibration and repair, re slotting or replacement.

3) After repairing the mechanical seal, it should be reassembled and subjected to pressure testing before being put back into normal operation.