HOW TO INSTALL AND DISASSEMBLE MECHANICAL SEALS IN CENTRIFUGAL PUMPS

The liquid in the centrifugal pump and the pressure outside the pump are different, and leakage will occur along the shaft. For this purpose, a sealing device needs to be set, which is called a shaft seal. There are three types of pump seals: gland packings, mechanical seals, floating seals. The mechanical seal has the advantages of minimal leakage, long life, no adjustment, and minimal shaft wear. It is widely used in various types of centrifugal pumps, especially for pumps with high head (pressure), the role of mechanical seals is more important.

The precision requirements for the manufacture and installation of mechanical seal components are strict. Improper installation will affect the performance of the machine's seal, and severely cause the seal to fail or make the pump unable to work properly. Therefore, the mechanical seal must be installed correctly.

1. Preparation and Precautions of Installation

1) Check whether the model and specifications of the installed mechanical seal are correct and whether the quality meets the standard.

2) Before installing the impregnated graphite ring, a hydrostatic test should be carried out. The hydrostatic pressure is not less than 1.5 to 2.5 times the working pressure. Water droplets and sweating should not appear on the outer surface of the graphite ring. If the above experimental conditions are not available, the assembly static pressure test can be carried out after the installation of the seal and before the pump is started. This is to identify the pressure resistance of the graphite ring.

3) The end of the anti-rotation groove and the top of the anti-rotation pin should maintain an axial gap of 1 ~ 2mm to avoid buffer failure.

4) The spring seals should note that the rotation direction of the spring should be the same as the rotation direction of the shaft. If the direction is wrong, the seal will fail. If the rotation direction of the shaft is ignored during installation , the mechanical seal is likely to be reversed, then the front and rear mechanical seals do not work.

5) Check whether the mechanical sealing component is damaged, especially whether the end face of the dynamic and static ring is damaged. If damage is found, it must be repaired or replaced. Each component must be cleaned with gasoline to keep the surface (especially the friction end surface) free of dust, iron filings or foreign objects.

2. Installation of the Mechanical Seal and Its Precautions

The installation position of the mechanical seal must be determined after the relative position of the rotor and the pump body is fixed. The positioning dimension can be measured according to the installation size of the seal and the position of the static ring in the gland. The accuracy of the positioning size is an important indicator to measure whether the mechanical seal installation is successful and the pump sealing effect is good. Pay attention to the following precautions during installation.

1) Avoid installation deviation during installation. The tightening of the gland should be carried out after the coupling is aligned. The tightening screw should be tightened evenly to prevent the flange surface from tilting. Check the points with a feeler, and the error is not greater than 0.05mm. At the same time, check the outer diameter matching clearance and concentricity of the gland and shaft. The four sides should be even.

2) The amount of spring compression.It must be carried out in accordance with the regulations, not allowed to be too large or too small, the error is ≤ + 2mm. If the compression is too large, it will increase the specific pressure of the cross section, thereby accelerating the wear of the end face. If the compression is too small, the specific pressure of the end face of the dynamic and static ring will be insufficient, making the sealing effect poor or completely unable to play a sealing role.

3) After the moving ring is installed, it must be ensured that it can move flexibly on the shaft.

4) After the mechanical seal and other parts of the pump are all installed, the hand truck and the pump shaft should rotate more easily and evenly.

3. Disassembly of the Mechanical Seal and Its Precautions

The disassembly order of the mechanical seal is the reverse of the installation. Take care of the process of disassembling the mechanical seal. Do not use a hammer or a flat shovel to avoid damaging the sealing components. It cannot be forcibly disassembled if there is dirt, it should be cleaned and then disassembling it.