Some key points for the installation and removal of mechanical seals

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There should be a thin layer of liquid between the sealing rings of a mechanical seal, which serves several functions: 1. To support most of the hydraulic load acting on the seal. 2. As a lubricant, it reduces the frictional heat generated by the seal ring. 3. Minimize rough contact, thereby reducing the wear rate. 4. As a heat transfer medium, it transfers thermal energy from the immediate area of the sealing ring. Before we disassemble the mechanical seal, we need to consider the following points: 1. Where is the main leak occurring? 2. Are there any debris on the external components? 3. Have any eccentricities been observed in the shaft or rotating sealed components? 4. Are there any system-related vibrations/noises (such as cavitation, misalignment)? 5. Is there localized heat generation in the “pump” or seal? 6. Is the leakage intermittent under different conditions, such as at different temperatures? 7. What type of leakage: spraying, droplets, stream, or flow into a pipe? 8. Is there any axial clearance in the bearing? 9. In the case of double mechanical seals, check whether the barrier fluid supply is functioning properly. 10. Relative position of the seals on the shaft? During the process of removing the seal, we must pay attention to the following points: 1. What is the condition of the gasket and the mating surfaces? 2. What about the condition and dimensions of the shaft? 3. Machine blockage/sealed cavitation? 4. Is it loose or tight when fitted onto the shaft? 5. Corrosion of the machine? 6. Are there any sealed fragments inside the machine? 7. Are there any reference marks at the position where it is sealed and mounted on the shaft? 8. Relative hardness of the shaft at the sealed portion? When removing the seal, we need to pay attention to the following points: 1. During the removal process, it is essential to be extremely careful to avoid any damage that might conceal the true cause of the seal failure ； 3. When removing components, it is necessary to observe carefully and keep records before moving on to the next component ； 4. The observed faults must be classified, such as wear, dry running, and noises from the sealing rings. Installation of mechanical seals: Ensure that the installation cavity is clean and free of any foreign particles. The shaft or sleeve used in conjunction with the mechanical seal must have the correct dimensions, a smooth surface, good straightness, and no burrs, sharp corners, scratches, or deep abrasions. Seal all holes in the sealing chamber that are not in use during the operation of the mechanical seals. The end face of the sealing chamber must be clean, smooth, and perpendicular to the axis. The two casings of a horizontal split-case pump must fit together properly; there are gaskets between the two casings, and all sharp corners and burrs on the surface of the sealing chamber must be removed. 　　Check that the gap between the wear ring and the impeller of the pump is appropriate; the shaft must rotate freely, as vibrations caused by friction or an improper gap can lead to seal damage. When using a shaft sleeve, ensure that it is properly sealed to the shaft to prevent leakage beneath it. 　　Ensure that all mounting screws are tightened. When set screws are used to provide sealing and drive between the shaft, the shaft should have countersunk holes to reinforce the connection. When tightening the gland bolts, do so smoothly and without applying elastic force to the gland. Use equally spaced gland plates with 4 or more screws wherever possible. When tightening the gland bolts, use a feeler gauge to check the gap between the shaft and the gland; this is particularly important when the sealing chamber does not provide guidance for the gland, as the gland must be precisely centered. 　　 Before starting the pump, perform a static test of the seal under pressure; minor adjustments can be made to the gland nuts to prevent leaks that may occur at the gland gaskets. 　　 Do not run the mechanical seal dry. Under specific circumstances, for flushing and cooling connections, the manufacturer’s operating instructions must be followed. Ensure that the pump’s inlet and outlet are open, and that there is a positive liquid level pressure before starting the pump. The same should be done when checking whether the rotation direction is correct and adjusting the motor connections. Check whether the model, specifications, and quantity of the mechanical seals meet the requirements of the design drawings, and inspect all components (especially the sealing surfaces and auxiliary sealing rings) for any signs of damage, deformation, cracks, etc. If any defects are found, they must be replaced or repaired. Check whether the shaft’s runout, swing, and deflection meet the technical requirements, whether the sealing chamber conforms to the installation dimensions, and whether the sealing end cover is perpendicular to the shaft. The general requirement is that the shaft’s runout should not exceed ±0.5 mm ； The shaft swing amount (at the rotating ring seal) shall not exceed 0.06 mm ； The maximum deflection of the shaft shall not exceed 0.05 mm ； The allowable deviation of the non-perpendicularity of the contact plane between the sealed end cover and the gasket relative to the center line is 0.03–0.05 mm. Tightening the gland should be carried out after the coupling has been aligned. The bolts should be tightened evenly to prevent skewing of the gland cross-section; a feeler gauge or special tool should be used to check each point, with the error not exceeding 0.05 millimeters. Check the fit clearance (and concentricity) between the gland and the outer diameter of the shaft or sleeve; it must be even around the perimeter, and a feeler gauge should be used to ensure that the tolerance at each point is no more than 0.10 millimeters. Here are some typical observations regarding wear/damage to the sealing ring: When wide wear tracks appear, it is generally related to the radial vibration of the moving ring, which exacerbates excessive end-face wear ； The wear path is \"off-center,\" which is generally related to the radial offset of the stationary ring/sealing gland, thereby increasing the uneven pressure load on the end face ；