Pump maintenance: matters needing attention in mechanical seal disassembly and assembly

Mechanical seal is one of the most effective ways to seal the body of a rotating machine. Its machining accuracy is relatively high, especially for the dynamic and static rings. If the disassembly and assembly method is not suitable or used improperly, the assembled mechanical seal will not only fail to meet the For the purpose of sealing, it will damage the assembled sealing elements.

1. Precautions when disassembling

1) When disassembling the mechanical seal, it is strictly forbidden to use a hand hammer and a flat shovel to avoid damage to the sealing element.

2) If there are mechanical seals at both ends of the pump, care must be taken during the disassembly process to prevent one from neglecting the other.

3) For the mechanical seal that has been used, if the sealing surface moves when the gland is loose, the dynamic and static ring parts should be replaced, and should not be re-tightened for continued use. Because after loosening, the original running track of the friction pair will change, and the sealing of the contact surface will be easily damaged.

4) If the sealing element is adhered by dirt or condensate, remove the condensate before disassembling the mechanical seal.

2. Precautions during installation

1) Before installation, carefully check whether the number of assembled sealing parts is sufficient and whether each component is damaged, especially whether the dynamic and static rings have defects such as bumps, cracks and deformation. If there is a problem, it needs to be repaired or replaced with a new spare part.

2) Check whether the chamfer of the shaft sleeve or gland is appropriate, if it does not meet the requirements, it must be trimmed.

3) The components of the mechanical seal and their related assembly contact surfaces must be cleaned with acetone or anhydrous alcohol before installation. It should be kept clean during installation, especially the dynamic and static rings and auxiliary sealing elements should be free of impurities and dust. Apply a layer of clean engine oil or turbine oil to the surfaces of the dynamic and static rings.

4) Tightening the gland should be done after the coupling is aligned. The bolts should be tightened evenly to prevent the section of the gland from being skewed. Check each point with a feeler gauge or a special tool, and the error should not be greater than 0.05 mm.

5) Check the matching clearance (and concentricity) between the gland and the outer diameter of the shaft or bushing. It must be uniform around it. Use a feeler gauge to check that the tolerance at each point is not greater than 0.10 mm.

6) The amount of spring compression should be carried out according to the regulations. It is not allowed to be too large or too small. The required error is ±2.00 mm. If it is too large, it will increase the specific pressure of the section and accelerate the wear of the section. If it is too small, it will cause insufficient specific pressure and cannot play a sealing role. After the spring is installed, it must move flexibly in the spring seat. When using a single spring, pay attention to the direction of rotation of the spring. The direction of rotation of the spring should be opposite to the direction of rotation of the shaft.

7) After the moving ring is installed, it must keep moving flexibly. After pressing the moving ring against the spring, it should spring back automatically.

8) Put the static ring sealing ring on the back of the static ring first, and then put it into the sealing end cover. Pay attention to protect the static ring section, ensure the verticality of the static ring section and the center line of the end cover, and align the anti-rotation groove on the back of the static ring with the anti-rotation pin, but do not make them touch each other.

9) During the installation process, it is not allowed to directly hit the sealing element with tools. When it is necessary to hit, it must be hit with a special tool to prevent the damage of the sealing element.