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Multistage centrifugal pump common parts failure and solutions

27 Nov 2023Email

        The fault analysis and treatment of multistage centrifugal pump components are as follows:

multistage pump(30)

1. Impeller and mouth ring:

        The blades of an impeller are often damaged by cavitation, inhalation of solid matter, or metal impurities. Wear of the mouth ring (also known as the seal ring) is usually caused by improper installation or loosening of the back cap of the impeller. If the ring is severely worn, the impeller needs to be replaced. If the wear is light, you can try to repair it.

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2. Balancing device:

        When the balance disc and balance ring wear too much (usually more than 2mm) or the surface is not flat, it can be repaired. This includes soldering or grinding the grooves on the pump housing and adding a 3mm thick teflon gasket at the junction of the balance ring and the pump housing. This eliminates unevenness while maintaining the proper hardness of the gasket. If the wear is serious, a new balance ring and balance plate should be replaced.

3. Mechanical seal:

        Mechanical seal is the key pump component, its performance directly affects the normal operation of the pump. Mechanical seal leakage problems account for more than 50% of service pump leaks. Leakage will cause the axial displacement of the pump rotor to increase, so that the interference between the auxiliary seal and the shaft will increase, and the moving ring can not move freely on the shaft. When installing the mechanical seal, it should be ensured that the axial displacement of the shaft is less than 0.1mm, and the interference between the auxiliary seal and the shaft is moderate to ensure the normal operation of the radial seal and the moving ring.

4. Pump shaft:

        The pump shaft is the core component of the pump, which is installed with the impeller and shaft sleeve, and rotates in the pump body at high speed. The bending of the pump shaft and the coaxiality deviation between the bearing seat and the pump shaft will lead to the wear of the impeller, guide impeller, pump housing, sealing ring and shaft sleeve, and increase the vibration and axial thrust of the pump body. As long as the pump shaft is not cracked or severely surface worn or bent, it can be repaired. The bending amount of the shaft should not exceed 0.06mm, otherwise it needs to be straightened.

5. Bearing temperature:

        High bearing temperatures can cause bearing damage. Factors that cause the bearing temperature rise to be too high include poor balance drum effect, excessive residual axial force, unqualified lubricating oil, insufficient oil or impurities in the oil chamber. In addition, excessive bearing Angle error or insufficient bearing clearance may also lead to excessive bearing load.

6. Rotor axial displacement:

        After installation, the axial displacement of the rotor needs to be measured. First of all, before installing the balance disc, install a shaft sleeve in the position of the balance disc, and lock it with all levels of the rotor into a rigid body with a nut. Then, push the rotor in the suction direction and measure the distance a from the shoulder to a plane of the pump body. Next, pull the rotor towards the discharge side, measure the distance b, and the total displacement is a-b. If the measured value is greater than the given value by 1mm, the impeller needs to be replaced. If the axial displacement is too large, a smooth, uniform thickness adjustment pad can be added between the balance disc and the balance ring.

7. Coupling clearance:

         In the process of multistage centrifugal pump operation, with the wear of the balance plate, the rotor will move to the suction side, so it is necessary to adjust the clearance of the coupling properly during maintenance. Taking into account the influence of the thermal expansion of the pump shaft, the clearance of the coupling should be 2-3mm larger than the specified value.

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