Common Parts Failure and Maintenance of Multi-stage Centrifugal Pump

Category: Water pump knowledge

2024-05-22

Multi-stage centrifugal pump pump shaft is equipped with two or more impellers in series, it is relative to the general single-stage centrifugal pump, can achieve higher head; relative to the piston pump, diaphragm pump and other reciprocating pump, can pump a larger flow. Multi-stage centrifugal pump has high efficiency and can meet the needs of high lift and high flow conditions. It has been widely used in petrochemical, chemical, electric power, construction, fire protection and other industries.

Because of its particularity, compared with single-stage centrifugal pump, multi-stage centrifugal pump has different and higher technical requirements in design, use, maintenance and repair. It is often people's negligence or thoughtlessness in some details, which makes the multi-stage centrifugal pump frequently abnormal wear, vibration, shaft holding and other failures after it is put into use, and also causes downtime.

Multi-stage centrifugal pump parts fault analysis and treatment are as follows:

1. Rotor axial displacement:

After installation, the axial displacement of the rotor needs to be measured. First, before installing the balance disc, install a shaft sleeve at the position of the balance disc, and lock it with the rotor at all levels into a rigid body with a nut. Then, push the rotor in the suction direction and measure the distance a from the shaft shoulder to a certain plane of the pump body. Next, the rotor is pulled to the discharge side, the distance B is measured, and the total displacement is a-b. If the measured value is greater than the given value of 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 plate and the balance ring.

2. Coupling clearance:

During the operation of the multi-stage centrifugal pump, with the wear of the balance disc, the rotor will move to the suction port side, so the gap of the coupling needs to be properly adjusted during maintenance. Taking into account the thermal expansion of the pump shaft, the gap of the coupling should be 2-3mm larger than the specified value.

3. Bearing temperature:

High bearing temperatures may cause bearing damage. The 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 cavity. In addition, excessive bearing angle error or insufficient bearing clearance may also cause excessive bearing load.

4. Pump shaft:

The pump shaft is the core component of the pump, which is equipped with the impeller and the shaft sleeve and rotates at high speed in the pump body. The bending of the pump shaft and the deviation of the coaxiality between the bearing seat and the pump shaft will cause the wear of the impeller, the guide impeller, the pump casing, the sealing ring and the shaft sleeve, and increase the vibration of the pump body and the axial thrust. As long as the pump shaft has no cracks or severe surface wear or bending, it can be repaired. The bending of the shaft should not exceed 0.06mm, otherwise it needs to be straightened.

5. Mechanical seal:

Mechanical seal is a key pump component, and its performance directly affects the normal operation of the pump. The leakage of mechanical seal accounts for more than 50% of the leakage of maintenance pump. Leakage will cause the axial displacement of the pump rotor to increase, so that the interference between the auxiliary seal and the shaft increases, and the moving ring cannot move freely on the shaft. When installing the mechanical seal, ensure 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.

6. Impeller and mouth ring:

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

7. Balancing device:

When the balance disc and balance ring are worn too much (usually more than 2mm) or the surface is uneven, it can be repaired. This includes welding or grinding the groove on the pump casing, and adding 3mm thick PTFE gasket at the junction of the balance ring and the pump casing. This eliminates irregularities while maintaining moderate hardness of the gasket. If the wear is serious, replace the new balance ring and balance plate.

Repair and maintenance of multistage pump

First of all, the daily maintenance of multi-stage pump is very necessary. Maintenance includes cleaning, inspection, lubrication and tightening. During use, some impurities and dirt will inevitably be produced in the pump body. If it is not cleaned in time, it will cause the inlet and outlet of the pump to be blocked and affect the normal operation of the pump. Therefore, we should regularly clean the pump body. At the same time, we also need to check whether the rotor and bearings in the pump body are worn or malfunctioning, and if so, they need to be replaced in time. In addition, the lubricating oil in the pump body also needs to be replaced regularly to ensure the lubrication effect inside the pump body.

Secondly, the troubleshooting of multi-stage pumps also requires professionals. In the process of using multi-stage pumps, various failures may be encountered, such as water leakage of the pump body, excessive noise, and unstable operation. If we encounter a failure, we need to find the cause of the failure and repair or replace it accordingly. However, due to the complex structure of the multi-stage pump, it is difficult to accurately diagnose and solve the problem without professional maintenance technology. Therefore, we recommend that in the event of a failure, it is best to find professional maintenance personnel to repair it.

Finally, we need to pay attention to the safe use of multi-stage pumps. When using a multi-stage pump, you need to pay attention to comply with relevant operating procedures, such as the need to heat the liquid in a low temperature environment, and must not be forced to start. In addition, it is necessary to pay attention to whether the operation of the pump is abnormal. If any abnormality is found, it should be stopped in time for inspection to avoid safety accidents.

To sum up, the repair and maintenance of multi-stage pump is very important, only regular maintenance and inspection, and in the event of failure to seek professional maintenance personnel to repair, in order to ensure the normal operation of multi-stage pump, but also to protect the safety of users.

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