In the process of industrialization, the role of multistage centrifugal pumps in industrial production has become increasingly prominent. In the industrial production, the multi-stage centrifugal pump has the characteristics of good controllability, high stability, high cost performance and strong input pressure. The application of multi-stage centrifugal pumps in industrial production can significantly improve the production efficiency of various industries, which is one of the reasons that are highly valued by relevant departments and industries. Based on the study of the structural characteristics of multi-stage centrifugal pumps, this paper starts with the failures of multi-stage centrifugal pumps in industrial production and how to maintain them. The detailed analysis and maintenance of the problems in the operation of multi-stage centrifugal pumps are analyzed in detail.
Centrifugal pumps are commonly used in liquid delivery equipment in industrial production. However, due to the harsh working environment of most centrifugal pumps, coupled with the multi-stage centrifugal pump and the single two-stage centrifugal pump, the structure is more complicated, the design is more difficult, the use is more cumbersome, and the later maintenance cost is higher. . If the staff is slightly negligent during use, the failure rate will increase. This will inevitably affect the production efficiency of the enterprise, increase the cost, and may lead to the service life of the multi-stage centrifugal pump, causing serious economic losses. Here we have made a detailed analysis of the routine maintenance and overhaul of multistage centrifugal pumps based on the management of multistage centrifugal pumps and the long-term working experience based on the use of multi-stage centrifugal pumps.
1. How multistage centrifugal pumps work
The components of the multistage centrifugal pump are: pump body, pump core and pump cover. The pump foot is all welded on the horizontal section of the pump body, and the assembled pump core is loaded into the pump body of the centrifugal pump, and the pump cover seals the high pressure liquid on the convex surface of the pump body. The main components of the pump core include: vane, rotor parts, suction body and middle section.
In practical applications, in order to make the multistage centrifugal pump work better, we must first understand the working principle of the multistage centrifugal pump. The liquid delivered by the multistage centrifugal pump will be discharged from the pump body under certain pressure conditions. The suction inlet enters, and then under the action of the impeller, both the kinetic energy and the potential energy of the liquid are increased, so that the liquid enters behind the vane, which promotes the mutual exchange of the potential energy and the kinetic energy of the liquid, thereby making the inner guide vane of the pump core The anti-blade is subjected to hydraulic action and is gradually transported to the impeller inlet of the next stage.
Due to the continuous input of liquid, the blades at all levels are subjected to the same pressure, and the liquid transported through the guide vanes will all reach the annular chamber of the pump body. The final result is that the delivered liquid passes through the impeller outlet and reaches the pipeline. Multi-stage centrifugal pumps have a wide range of applications, and they play an extremely important role in chemical, mineral or petroleum industry multistage centrifugal pumps.
2. Structural features of multistage centrifugal pumps
There are two types of multistage centrifugal pumps that are often used by enterprises or units: volute multistage centrifugal pumps and segmented multistage centrifugal pumps. The volute multi-stage centrifugal pump is a medium-open structure, which is convenient to repair and is quite advantageous for the symmetrical arrangement of the impeller, and the axial force acting on the rotor. However, the multi-stage centrifugal pump of this structure is designed to be inferior in craftsmanship, and the shape of the pump body and the cap will become more and more complicated as the number of stages increases.
When the size of the pump body is increased, it is necessary to configure some interstage flow passages to complete the connection between the stages, which will make the shape of the pump body more complicated. Based on the above characteristics, the application range of the volute multistage centrifugal pump is limited. The structural features of the segmented multistage centrifugal pump are relatively compact and suitable for standardization and generalization. The lift of this type of pump is determined by the number of stages of the pump, so the segmented multistage centrifugal pump has a wide lift range.
3. Analysis and repair of common faults of multistage centrifugal pumps
3.1 Impeller and ring
In most cases, the blades of the pump impeller are inhaled by a large amount of solid or metal impurities, and the impeller is damaged by cavitation. If the pump impeller blades are often subject to cavitation, it is not only necessary to replace the new impeller, but should consider whether the process conditions can not fully meet the needs of the pump. The mouth ring is also the sealing ring of the pump body. Most of its wear is caused by improper control during the installation of the radial and axial runouts.
It is also possible that the wear of the impeller’s back cap is loose. In the process of use, if the mouth ring wear is too serious, it must be replaced immediately, otherwise it will cause the pump efficiency to decrease and the output to be insufficient. When a very small number of rings are worn out, it will cause a loop to lock or a larger fault. If the ring wear is lighter, the technician can repair it.
3.2 Pump shaft
The shaft is the most central component in the pump body. If the rigidity and straightness of the shaft cannot fully meet the specified specifications, the pump shaft will cause the rotor to move unbalanced, thereby increasing the vibration of the pump body. In some special cases, it will also cause the friction between the static and dynamic parts to damage the pump body, which will cause an unexpected chain reaction. The taper of the pump journal under normal conditions should also be determined according to the diameter and speed of the pump impeller. Therefore, each time the technician performs maintenance, the pump shaft should be visually inspected. If conditions permit, color inspection can be performed. If cracks or other causes are found, repair or replace it immediately.
3.3 Balance device
The axial force of the multistage centrifugal pump in normal operation far exceeds that of the single stage centrifugal pump. Therefore, when the multistage centrifugal pump is working, it is necessary to use a certain balance tube or balance disc to eliminate excessive axial force. However, the balance tube must be unobstructed. The balance plate should measure the thickness periodically and calculate the amount of wear. In addition, for some large multi-stage centrifugal pumps, in order to improve the working condition of the balancing device, the back-to-back impeller arrangement can be used to offset most of the axial force. Improve the balance device at work.
3.4 Machinery Seal
Mechanical seals are also commonly referred to as end seals under normal conditions. The pump body has a pair of end faces perpendicular to the axis of rotation. Under the action of the liquid inflow to generate pressure and supplement the mechanical external elastic force, the two end faces, that is, the static face and the moving face, will remain relatively sliding and closely fit to prevent liquid leakage. . Mechanical seals are high-precision mechanical components in multistage centrifugal pumps, and their correct installation and operation are directly related to their service life. In the maintenance of the pump body in the later stage, the maintenance of the mechanical seal accounts for more than half of the total maintenance.
4. Multistage centrifugal pump maintenance
4.1 To ensure good lubrication
Regardless of the type of bearing used in the pump body, there are generally two types of bearings, rolling and sliding. Both need to ensure that they are well lubricated. In order to reach the contact parts of the bearing, it can always be in the lubrication of the oil film. The most important thing is that the lubricating oil must be selected according to the requirements of the equipment manufacturer. It is forbidden to be contaminated by water. Finally, it should be noted that during the overhaul process, never add excessive oil to the rolling bearing, which will cause the bearing’s heat dissipation performance to drop significantly, eventually causing the bearing to malfunction. Welcome to pay attention to the public number of the pump circle. For a plain bearing, it must be carefully checked when it is installed. Because it has a mounting requirement in the direction of rotation, it must be aligned with the direction in which the rotor rotates to establish a stable oil film. Otherwise, the wrong installation direction will deteriorate the lubrication condition of the bearing, thus shortening the service life of the bearing.
4.2 Strengthen the maintenance of wearing parts
The wearing parts of the multi-stage centrifugal pump mainly include: sealing ring, oil cup and gaskets of various parts. In the inspection and maintenance of the multi-stage centrifugal pump by the staff, we must not only pay attention to the detection and maintenance of the main parts of the equipment, but ignore the inspection and timely replacement of the vulnerable parts in the equipment. According to the survey, some enterprises have overhauled a multi-stage centrifugal pump. Only the main components are well maintained. The seals at the oil cup interface are not carefully checked, and the pump body is started. As a result, the seal gasket is damaged. The aging of the oil cup gasket gradually leaks outward, eventually causing the lubricating oil to leak out completely, causing the bearings to completely bite together, causing unnecessary economic losses to the enterprise.