I. Introduction

 

Centrifugal pumps play a vital role in industrial production. They are widely used in numerous industries such as chemical, petroleum, pharmaceutical, electric power, and metallurgy, serving as the key equipment for fluid transportation. In industrial production lines, centrifugal pumps can ensure the continuity and stability of the technological process, providing a continuous supply of liquid or gas for many production links. Their highly efficient transportation capabilities, enabling the conveyance of a large amount of media with relatively low energy consumption, are of great significance for improving industrial production efficiency and reducing costs. Moreover, in some special environments, centrifugal pumps can effectively prevent leakage and pollution through the selection of sealing structures and materials, thus ensuring production safety.

 

Given the indispensability of centrifugal pumps in industrial production, it is particularly necessary to explore the factors that affect the working efficiency of centrifugal pumps. Only by having a in-depth understanding of these factors can we better optimize the performance of centrifugal pumps and improve their working efficiency, thereby bringing greater benefits to industrial production.

 

II. Factors Affecting the Working Efficiency of Centrifugal Pumps

 

(I) Pump Efficiency Itself

Among the many factors affecting the working efficiency of centrifugal pumps, the efficiency of the pump itself plays a fundamental role. Under the same working conditions, the efficiencies of different centrifugal pumps may vary by more than 15%. This is because different pumps differ in aspects such as design, manufacturing process, and material selection. Some high-quality centrifugal pumps are more reasonably designed and can better adapt to the working environment, thus improving the working efficiency. However, some low-quality pumps may have problems such as unreasonable structures and non-durable materials, resulting in low efficiency.

 

(II) Operating Conditions

The operating conditions of centrifugal pumps also have a significant impact on their working efficiency. When the operating conditions of a centrifugal pump are below the rated conditions, the pump efficiency will decrease and the energy consumption will be high. This is because when operating below the rated conditions, the parameters such as flow rate and head of the pump cannot reach the optimal state, thus leading to a decline in efficiency. For example, in actual production, if the flow rate demand of a centrifugal pump is less than the rated flow rate, the pump may operate in a low-efficiency area, wasting energy.

 

(III) Motor Efficiency

The motor efficiency basically remains unchanged during operation. Therefore, it is crucial to select a high-efficiency motor. A high-efficiency motor can provide stable power for the centrifugal pump, thereby improving the efficiency of the entire pump unit. If the motor efficiency is low, even if the centrifugal pump itself has a high efficiency, the working efficiency will also be affected due to insufficient power.

 

(IV) Mechanical Efficiency

Mechanical efficiency is mainly related to the quality of design and manufacturing. After the pump is selected, the impact of subsequent management on mechanical efficiency is relatively small. High-quality design and manufacturing can ensure close cooperation between the various components of the centrifugal pump, reducing mechanical friction losses and improving mechanical efficiency. However, if there are defects in the design or manufacturing, it may lead to an increase in friction between the components, reducing the mechanical efficiency.

 

(V) Hydraulic Losses

Hydraulic losses include hydraulic friction and local resistance losses. With the increase in the running time of the centrifugal pump, the surfaces of components such as impellers and guide vanes will gradually wear, which will lead to a decrease in hydraulic efficiency. For example, the wear on the surface of the impeller will cause more vortices and resistance in the liquid flow process, thereby increasing hydraulic losses. In addition, local resistance losses will also increase with the unreasonable layout of the pipeline.

 

(VI) Volumetric Losses

Volumetric losses, also known as leakage losses, are related to design, manufacturing, and subsequent management. During the operation of the centrifugal pump, the friction between components will cause the gaps to increase, thereby reducing the volumetric efficiency. For example, the increase in the gaps in areas such as the impeller seal ring, between stages, and the axial force balance mechanism will increase the liquid leakage, reduce the output flow of the pump, and further affect the working efficiency.

 

(VII) Other Factors

In addition to the above factors, there are also some other factors that can affect the working efficiency of centrifugal pumps. For example, the blockage of the filter tank and the entry of air into the pipeline will cause cavitation and idling. Insufficient preparation work before starting will cause the cavitation phenomenon, reducing the pump efficiency. The blockage of the filter tank will lead to a decrease in the liquid flow rate, increasing the load on the pump and reducing the efficiency. The entry of air into the pipeline will cause bubbles to form in the pump, affecting the normal transportation of the liquid and even causing the pump to fail to work. If the basic operating procedures such as warming the pump, turning the pump by hand, and priming the pump are not thoroughly executed before starting, the cavitation phenomenon will occur when the pump is started, causing the pump to produce loud noise and severe vibration, reducing the pump efficiency.

 

III. Strategies for Improving the Working Efficiency of Centrifugal Pumps

 

(I) Selecting Appropriate Centrifugal Pumps

Select centrifugal pumps whose parameters are close to the actual operating conditions to ensure operation in a high-efficiency state.

When selecting a centrifugal pump, the actual operating conditions should be fully considered to ensure that the parameters of the selected pump match the actual requirements. For example, according to the required flow rate, head, and other parameters, referring to the types and selection principles of centrifugal pumps, select from different types such as single-stage centrifugal pumps, multi-stage centrifugal pumps, vertical centrifugal pumps, and submersible centrifugal pumps. If the flow rate demand is large and the head requirement is not high, a single-stage centrifugal pump can be selected; if high heat and high-pressure transportation are required, a multi-stage centrifugal pump is more appropriate. At the same time, the appropriate pump material should be selected according to the characteristics of the liquid. For example, corrosion-resistant materials should be selected for corrosive liquids to ensure the pump's long-term stability.

 

(II) Applying Energy-saving Technologies

The frequency conversion energy-saving technology can make the pump always operate in the high-efficiency area.

The frequency conversion speed regulation technology is one of the important means to improve the efficiency of centrifugal pumps. By adjusting the frequency of the motor, the rotational speed of the pump can be changed according to the actual operating conditions, enabling the pump to maintain high-efficiency operation under different loads. For example, when the production load decreases, the rotational speed of the motor is reduced, thereby reducing the flow rate and head of the pump, avoiding energy waste under low loads. For centrifugal pumps whose design parameters are greater than the actual operating conditions, after installing the frequency conversion speed regulation device, they can always operate in the high-efficiency area, effectively improving the energy utilization efficiency.

Promote the application of new energy-saving products such as permanent magnet speed regulation motors and dual-power motors.

New energy-saving motors such as permanent magnet speed regulation motors and dual-power motors have higher efficiency and stability. They can provide more reliable power for centrifugal pumps and reduce energy losses. Promoting the application of these new energy-saving products on major centrifugal pumps can significantly improve the efficiency of the entire pump unit and reduce running costs.

 

(III) Strictly Following Operating Procedures

Before starting, do a good job of turning the pump by hand, priming the pump, and other preparation work to prevent the cavitation phenomenon.

Strictly follow the operating procedures of the centrifugal pump. Before starting, turn the pump by hand, open the inlet valve, close the outlet valve perform exhaust and venting operations, and check whether the inlet pressure of the pump meets the requirements. This can effectively prevent the cavitation phenomenon caused by low supply liquid pressure and insufficient flow rate. Cavitation will cause the pump to produce loud noise and severe vibration, reducing the pump's efficiency. Therefore, doing a good job of preparation work before starting is crucial.

Regularly clean the filter tank to ensure the smoothness of the inlet liquid pipeline.

Regularly clean the filter tank and check the pipeline connections to avoid problems such as filter tank blockage and pipeline air entry. The blockage of the filter tank will lead to a decrease in the liquid flow rate, increasing the load on the pump and reducing the efficiency; the entry of air into the pipeline will cause bubbles to form in the pump, affecting the normal transportation of the liquid. Ensuring the smoothness of the inlet liquid pipeline can ensure the stable operation of the centrifugal pump and improve the working efficiency.

 

(IV) Regularly Conducting Detection and Maintenance

Regularly conduct pump efficiency detection on centrifugal pumps and promptly find out the reasons and solve the problems.

Regularly conduct pump efficiency detection on centrifugal pumps to be able to promptly discover the problem of pump efficiency decline. When the pump efficiency decreases, the reasons should be promptly found out. It may be due to the wear of components such as impellers and guide vanes, resulting in an increase in hydraulic losses, or the increase in the gaps between components, causing an increase in volumetric losses. Corresponding measures should be taken for different problems, such as repairing or replacing the worn components, adjusting the gaps, etc., to restore the high-efficiency operation of the pump.

 

IV. Conclusion

 

The working efficiency of centrifugal pumps is affected by multiple factors. Through the analysis of these factors and the adoption of corresponding improvement strategies, the working efficiency of centrifugal pumps can be effectively improved, ensuring that they play a greater role in industrial production.

The factors affecting the working efficiency of centrifugal pumps mainly include pump efficiency itself, operating conditions, motor efficiency, mechanical efficiency, hydraulic losses, volumetric losses and other factors. In actual application, it is necessary to comprehensively consider these factors and adopt scientific management and maintenance measures to improve the working efficiency of centrifugal pumps.

To improve the working efficiency of centrifugal pumps, the following strategies can be adopted:

Selecting appropriate centrifugal pumps: Select centrifugal pumps whose parameters are close to the actual operating conditions to ensure operation in a high-efficiency state. At the same time, select the appropriate pump material according to the characteristics of the liquid.

Applying energy-saving technologies: Adopt frequency conversion energy-saving technology to make the pump always operate in the high-efficiency area. Promote the application of new energy-saving products such as permanent magnet speed regulation motors and dual-power motors.

Strictly following operating procedures: Before starting, do a good job of turning the pump by hand, priming the pump, and doing other preparation work to prevent the cavitation phenomenon. Regularly clean the filter tank to ensure the smoothness of the inlet liquid pipeline.

Regularly conducting detection and maintenance: Regularly conduct pump efficiency detection on centrifugal pumps and promptly find out the reasons and solve the problems.

It is of great importance to conduct scientific management and maintenance of centrifugal pumps. This not only can improve the working efficiency of centrifugal pumps, and reduce energy consumption, but also can extend the service life of centrifugal pumps, reduce equipment maintenance costs, and bring greater benefits to industrial production. In actual operation, it is necessary to strictly follow the operating procedures, regularly conduct detection and maintenance, promptly discover and solve problems, and ensure that the centrifugal pump is always in a good working state.

In the world of centrifugal pumps, the impeller is like the heart, and the differences in its types have a crucial impact on the performance and applications of centrifugal pumps. Today, let's take an in-depth look at the wonderful changes brought about by different impellers in centrifugal pumps.

 

I. Open Impeller: The Unrestrained Master of Flow

Flow Characteristics

Centrifugal pumps with open impellers are "giants" in the field of flow. There are no shrouds on either side of its blades, and the liquid flows through it as if on an open road, with minimal restraint. This free-flowing environment enables it to easily handle the demand for large flow rates of liquid transportation. Imagine in the vast farmland irrigation scenario, where clear water is continuously pumped from the water source. Through the centrifugal pump with an open impeller, it's like opening a highway for water, allowing a large amount of water to quickly flow into the fields to satisfy the thirst of crops. In cases where there is an extremely high demand for flow rate and the transported medium is relatively clean and not prone to clogging, the centrifugal pump with an open impeller is undoubtedly the top choice.

 

Head and Efficiency Characteristics

However, everything has two sides. The open impeller is somewhat inferior in terms of head. Due to the relatively dispersed flow of the liquid, when the impeller rotates to transfer energy, it cannot effectively convert the energy into the pressure energy of the liquid as other types of impellers do, so the head is relatively low. Moreover, because there is no restraint from shrouds, more energy is dissipated during the flow of the liquid, and backflow phenomena are likely to occur at the inlet and outlet of the impeller, which makes its efficiency relatively low among several types of impellers. However, in some low-head and large-flow drainage scenarios like temporarily draining rainwater on construction sites, the centrifugal pump with an open impeller can still exert its unique advantages.

 

Anti-Clogging and Wear Resistance Characteristics

When it comes to anti-clogging, the open impeller is a champion. It is like a large inclusive pocket, allowing certain-sized solid particles or impurities to pass through the impeller along with the liquid. This is especially outstanding when transporting liquids containing more impurities, such as river water with sediment or wastewater with fibers. However, this inclusiveness comes at a cost. Solid particles are likely to come into direct contact with the impeller blades, and after long-term operation, the blade wear problem will be quite prominent, and the wear resistance is relatively poor.

 

II. Semi-Closed Impeller: The Practitioner of the Balance Principle

Flow and Head Characteristics

The semi-closed impeller has a shroud on one side and none on the other, as if finding a balance point between the open and closed impellers. In terms of flow rate, it is between the two, with a larger flow rate than the closed impeller and a smaller one than the open impeller. Its unique structure makes the flow path of the liquid relatively more regular, which to some extent increases the liquid flow velocity. In terms of head, it also shows a moderate level. In the multi-story building water supply system, when the floor is not particularly high, the centrifugal pump with a semi-closed impeller is like a precise "water transporter", able to provide residents with an appropriate amount of water and water pressure just right to meet the domestic water demand.

 

Efficiency and Applicable Medium

The efficiency of the centrifugal pump with a semi-closed impeller is also between that of the open and closed impellers. The shroud on one side reduces the dissipation of liquid energy, making its running efficiency higher than that of the open impeller. In some simple industrial processes, such as general material transportation systems, it can maintain a certain running efficiency while meeting the requirements of flow rate and head. In terms of applicable medium, it can handle liquids containing a small amount of impurities. For example, in the food processing industry, when transporting fruit juice with a small amount of pulp particles, the centrifugal pump with a semi-closed impeller can ensure a certain flow rate and head without being easily affected by impurities.

 

III. Closed Impeller: The Elite of Head and Efficiency

Head and Efficiency Characteristics

The centrifugal pump with a closed impeller is an "excellent student" in both head and efficiency. The design with shrouds on both sides allows the liquid to flow orderly in the flow channels inside the impeller, just like a train running on rails. When the impeller rotates, it can efficiently transfer mechanical energy to the liquid, enabling the liquid to obtain higher pressure energy and thus generate a higher head. In the chemical process, when it is necessary to transport the liquid to a higher position or overcome a large resistance, the centrifugal pump with a closed impeller is like a powerful "power amplifier", playing a crucial role. Meanwhile, this precise flow channel design and good sealing performance result in less energy loss during the flow of the liquid, and the gap between the impeller and the pump shell can also be precisely controlled, further reducing leakage losses and thus ensuring a higher efficiency. In the long-term operation and in large urban water supply systems that are sensitive to energy consumption, the centrifugal pump with a closed impeller, relying on its high-efficiency and energy-saving characteristics, safeguards the urban water supply.

 

Anti-Clogging, Wear Resistance and Applicable Medium

However, the closed impeller also has its "temper". Due to the relatively small and closed flow channels, it is very sensitive to solid particles and is prone to clogging the flow channels. However, its wear resistance is quite good. Under reasonable design conditions, the liquid mainly flows inside the flow channels, and the impeller blades have few opportunities to come into contact with solid particles. Moreover, we can choose wear-resistant materials to make the impeller to further improve its wear resistance. Therefore, it is mainly used to transport pure liquids, such as clear water, various oils, chemical solutions, etc. In the pharmaceutical industry for transporting liquid medicine, in the electronic industry for transporting ultrapure water and other occasions where the purity requirement of the medium is extremely high, the centrifugal pump with a closed impeller is irreplaceable.

 

In conclusion, centrifugal pumps with different impellers are like craftsmen with different skills, shining brightly in different fields and working conditions. Understanding their characteristics can help us make more informed choices when selecting centrifugal pumps, allowing these "water spirits" to better serve our production and life.

Lubrication: During the operation of a slurry pump, the possible intrusion of the conveyed medium, water, and other substances into the oil tank may affect the pump's normal operation. Therefore, it is necessary to check the quality and oil level of the lubricant frequently. The quality of the lubricant can be observed with the naked eye and analyzed by regular sampling. The amount of lubricating oil can be seen from the oil level mark.

For a new pump, the oil should be changed once after one week of operation. For a pump with replaced bearings during overhaul, the oil should also be changed. Because foreign substances enter the oil during the running-in of the new bearings and shafts, the oil must be changed. Thereafter, the oil should be changed once every quarter. The lubricating grease and lubricating oil used for chemical pumps should meet quality requirements. Tables 2-8 and 2-9 show the commonly used lubricating grease and lubricating oil for slurry pumps.

Vibration: During the operation of the pump, due to reasons such as poor quality of spare parts and maintenance, improper operation, or pipeline vibration, vibration often occurs. If the vibration exceeds the allowable value, the pump should be shut down for maintenance to prevent damage to the machine. Table 2-10 shows the allowable range of vibration values for slurry pumps.

Bearing temperature rise: During the operation of the pump, if the bearing temperature rises rapidly and after the temperature rise stabilizes, the bearing temperature is too high, which indicates that there are problems in the manufacturing or installation quality of the bearing; or the quality, quantity, or lubrication method of the bearing lubricating oil (grease) does not meet the requirements. If not dealt with in time, the bearing is in danger of being burned out. The allowable temperature for slurry pump bearings is <65°C for sliding bearings; and <70°C for rolling bearings. This allowable value refers to the allowable range of bearing temperature after running for a period of time. For a newly replaced bearing, at the initial stage of operation, the bearing temperature will rise relatively high. After running for a period of time, the temperature will drop somewhat and stabilize at a certain value.

The operating performance of slurry pump: During the operation of the pump, if there is no change in the liquid source and the opening degree of the valves on the inlet and outlet pipelines remains unchanged, but the flow rate or inlet and outlet pressure changes, it indicates that there is a fault in the pump or pipeline. The cause should be quickly identified and eliminated in time, otherwise, adverse consequences will be caused.

The size of the system resistance can be achieved by adjusting the opening degree of the inlet and outlet valves of the pump. For a determined pump system, when the outlet valve is fully opened, the system resistance is the smallest, and the corresponding flow rate is the largest, the head is the smallest, and the power is the largest. When the outlet valve is completely closed, the system resistance reaches a maximum value. At this time, the flow rate is zero, the head is the largest (a finite value), and the power is the smallest.

From this, the following points can be summarized:

When starting a slurry pump, in order to avoid overloading the prime mover, the outlet valve should be closed first and then opened slowly after the pump is started. In this way, it can avoid the superposition of the large starting load of the prime mover and the high power required by the pump when the outlet valve is fully opened, which may cause overloading of the prime mover.

As long as the pump chamber is filled with liquid (to avoid dry friction of the sealing ring, shaft seal, etc.), the slurry pump is allowed to operate for a short time when the outlet valve is closed. Except for the rapid temperature rise of the limited liquid in the pump chamber under the action of the rotating impeller, which has some adverse effects on the pump, there is no adverse effect on the prime mover. At this time, the load on the prime mover is the lightest.

During operation, any set of flow rates and heads within the performance range of the slurry pump can be obtained by adjusting the opening degree of the outlet valve. However, when the pump operates at the design operating point, its efficiency is the highest; the farther away from the design operating point, the lower the efficiency.

Unit sound: The sounds emitted by the pump during operation are some normal and some abnormal. For abnormal sounds, find out the cause and eliminate it in time. The following are roughly the reasons for the abnormal sounds of the pump.

Reasons on the fluid side: For example, insufficient inlet flow of the slurry pump causes cavitation and emits noise; air accumulation in the pump outlet pipeline causes water hammer and emits an impact sound.

Reasons on the mechanical side: The bearing quality does not meet the requirements or is damaged; the clearance between the moving and stationary parts of the pump is inappropriate, causing friction; shaft bending causes internal friction; parts are damaged and fall off; foreign objects fall into the pump, etc.

 

For details of the first part, please refer to the previous blog post.