Inspection and maintenance process regulations for mechanical seals of water pumps

To master the repair and maintenance of mechanical seals, one must first know the working principle of mechanical seals. The mechanical seal is a sealing device composed of two sealing elements (stationary ring and moving ring) that are perpendicular to the shaft, smooth and flat surfaces that are attached to each other and rotate relative to each other. It relies on the pressure of the sealing medium to generate an appropriate pressing force on the contact surface (end face) of the rotating dynamic ring and the static ring, so that the two end faces are tightly combined, and a very thin liquid film is maintained between the end faces to achieve sealing. purpose. This layer of liquid film has liquid dynamic pressure and static pressure, and plays the role of lubrication and balance force. The maintenance process of water pump mechanical seal mainly has the following aspects:

one. Cleaning and inspection of mechanical seals

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

1. Whether there are scratches, cracks and other defects on the surface of the dynamic and static rings. The existence of these defects will cause serious leakage of the mechanical seal. If conditions permit, special tools can be used to check whether the sealing surface is smooth. If the sealing surface is not smooth, pressure water will enter the sealing surface of the dynamic and static rings of the assembled mechanical seal, separate the dynamic and static rings, and the mechanical seal will fail. If necessary, tooling can be made for hydraulic test before assembly.

2. Check whether there are defects affecting the sealing of the dynamic and static ring seats. For example, whether there are defects such as scars on the mating surface of the dynamic and static ring seat and the dynamic and static ring sealing rubber ring.

3. Check whether the compensation spring of the mechanical seal is damaged and deformed, and whether the stiffness coefficient changes.

4. Check the sealing shaft sleeve for defects such as burrs and groove marks.

5. Clean and check whether there are cracks, pores and other defects in all sealing rubber rings, and measure whether the diameter of the rubber rings is within the working tolerance range.

6. The mechanical seal with pumping mechanism should also check whether there are cracks, broken wires and other defects in the helix of the screw pump.

two. Dimensional check of mechanical seal assembly technology

The maintenance process of mechanical seals is relatively complicated. To ensure that the assembled mechanical seals have no leakage, it is essential to check the technical dimensions of the mechanical seals.

1. Measure the size of the sealing surface of the moving ring and the static ring. 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 to cause the edges and corners of the end surface of the hard material to be embedded in the soft material. face up.

2. Check the gap between the moving ring, the static ring and the shaft or bushing. The inner diameter of the static ring is generally 1-2mm larger than the shaft diameter. For the moving ring, in order to ensure floating, the inner diameter is 0.5-1mm larger than the shaft diameter to compensate Vibration and deflection of the shaft, but the gap should not be too large, otherwise the moving ring sealing ring will be stuck and the mechanical sealing function will be damaged.

3. Check the tightness of the mechanical seal. The mechanical seal tightness we usually talk about is the specific pressure of the end face. The specific pressure of the end face should be appropriate. If it is too large, the friction surface of the mechanical seal will heat up, accelerate the wear of the end face and increase the friction power; if it is too small, it will easily leak. The specific pressure of the end surface is determined during the design of the mechanical seal, and we can only determine it by measuring the tight force of the mechanical seal during assembly. The usual measurement method is to measure the vertical distance from the end face of the installed static ring to the end face of the gland, and to measure the vertical distance from the end face of the moving ring to the end face of the gland. The difference between the two is the tight force of the mechanical seal.

4. Measure whether the length of the compensation spring changes. The change of the spring performance will directly affect the specific pressure of the mechanical seal end face. Generally, the length of the spring will be shortened after long-term operation, and the mechanical seal of the compensation spring on the moving ring will be deformed 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 cannot be assembled in place. This condition can damage the mechanical seal.