Water pump plays an important role in modern industrial production, but it will be affected by various problems in use, which will affect its normal operation. This paper discusses the requirements of pier design and pier design from the requirements and size determination of suction pipe, installation mode of water delivery pipe, selection of suction pipe material and water diversion mode, type of pressure pipe, laying mode and supporting mode of pipeline, and briefly analyzes the calculation and protection of water hammer of water pump, so as to further improve the design level of water pumps in China.

1 Factors affecting pump operation efficiency

1. 1 pump selection

During the operation of a pumping station, the operating efficiency of the pump is equal to the product of hydraulic efficiency, pump volumetric efficiency and mechanical efficiency, so the operating efficiency of the pump itself determines the operating efficiency of the whole pumping station. If the quality of the pump selected at the beginning of design is unqualified, the cavitation of the pump impeller will be aggravated. If the clearance of the sealing ring of the pump is too large or too small, it will reduce the working efficiency and service life of the pump.

1.2 vibration of water pump blades

The blades of water pump are generally single-stage blades. In order to better improve the operation characteristics of the pump, the diameter of the rotor part of the pump is generally much smaller than that of the impeller blade of the pump, which leads to the unbalanced mass and inertia moment produced by the variable frequency fan concentrated on the impeller blade. Therefore, when designing, impeller blades are generally designed as symmetrical structures. However, due to the manufacturing error of blades, it is generally difficult to achieve complete symmetry of impeller blades, and sometimes the pump has to run at high speed, which will cause huge moment of inertia. The transfer of moment of inertia to blades and crankshaft will cause excessive vibration of variable frequency fan.

1.3 pump lacks lubrication.

The working characteristics of the pump make the work of the pump not completely fixed, and it is unstable to reduce the design point of the pump as much as possible with only one crankshaft, which may bring energy loss through this unevenness. However, in the long-term operation of the rotating machinery inside the pump, insufficient lubrication will lead to severe friction between the rotating machinery, which will not only damage the mechanical equipment, but also greatly reduce the efficiency of the pump.

2 design requirements of suction pipe

2. 1 Selection of pipeline materials

The material of suction pipe should have the characteristics of good air tightness, strong corrosion resistance, safety and reliability, so its comprehensive performance should be considered when selecting the material of suction pipe. Stainless steel pipe has the advantages of high mechanical strength, thin wall, small specific gravity and low pressure loss, and is easy to install, maintain and replace, so it has been widely used in pumping station engineering. The service life of stainless steel pipes is generally only 20 ~ 30 years. When the service life of the pipeline is about to expire, it should be replaced and repaired in time. Rubber tube is also a common straw material at present. Stainless steel pipes are used for long-term or permanent pumping stations, and rubber pipes are generally used for temporary pumping stations.

2.2 Requirements for inlet pipeline

(1) No gas accumulation. The working principle of the suction pipe is to form a water absorption effect according to the pressure difference (vacuum degree) inside and outside the water pipe. When the pressure difference between the inside and outside of the water pump suction pipe is reduced to a certain extent, the gas dissolved in water is continuously separated because of the small vacuum degree in the pipe. If the influence of this factor on the pipeline is not seriously considered in the design, gas will accumulate in a certain section of the water absorption pipeline, forming an airbag, which will affect the normal water absorption of the water pipe.

(2) No air leakage. The suction pipe circulates the water through the pressure difference inside and outside the water pipe. Once the suction pipe leaks, it will cause great pressure loss in the water pipe, and in serious cases, the pump will not operate normally. At the same time, the water pipe leaks, the water in the pipe flows out, the outside air enters the water pipe, and the water output of the pump will be reduced, or even the water cannot be sucked. In general, the suction pipe adopts high-strength steel pipe with weldable joints, and the steel pipe buried deep in the soil should be coated with anti-corrosion coating.

(3) Do not inhale. If the inlet depth of the suction pipe is not enough, a large swimming vortex will be generated at the inlet of the suction pipe, which will bring a lot of air into the suction pipe and seriously affect the normal suction of the pump. In order to avoid vortex on the water surface of the suction well (building) and reduce the air intake at the suction port, the submerged depth of the suction pipe should be greater than 0.6m at the lowest water level. If the environmental conditions cannot meet the minimum submerged depth, the air intake can be reduced by installing a horizontal baffle at the inlet end of the suction pipe.

2.3 Selection of water diversion mode

(1) When the pumping station is close to the water source, the sediment concentration of the water source is low and the water level of the water source is basically unchanged, and the diversion flow of the pumping station is not large, the pipeline diversion mode can be selected. When the bank slope of the water source is slow, the inclined rod pipe diversion method is adopted, and when the bank slope of the water source is steep, the straight pipe diversion method is adopted.

(2) When the pumping station is close to the water source, the sediment concentration of the water source is high and the bank slope of the water source is steep, the culvert can be used to divert water.

(3) When the bank slope is slow and the water intake buildings such as pumping stations are far away from the water source, you can dig channels to take water. Trenching can shorten the service length of pressure pipeline and improve the economic benefit of the project.

2.4 Selection of connection forms of through-wall pipes

(1) flexible connection. Flexible installation is to improve the flexibility of installation. In order to reduce the influence of impact stress and temperature stress, flexible connection is generally used to connect through-wall pipelines for pumping stations with pumps and power machines higher than the check flood level. Ensure that the installed through-wall pipeline can freely expand and contract, and effectively resist impact load and temperature stress.

(2) Rigid connection. When connecting pipes, the similarities and differences between threaded connection and flange connection should be fully considered. The threaded connection is relatively simple, and better sealing effect can be achieved through the threaded connection of the pipe and sealing with the raw material belt. When connecting pipe threads, it is necessary to master the tightness of the threads, and when pre-tightening by hand, it is necessary to ensure a certain amount of activity after tightening the pipe threads. When using adjustable wrench for secondary tightening, attention should be paid to the magnitude of pre-tightening force, and thread damage should not be caused by over-tightening. If possible, it can be tightened with a torque wrench, which can ensure that the pre-tightening force meets the requirements. After threaded connection, the exposed oil, hemp and raw material belts should be removed, and the pipeline that is easy to corrode should be treated with anti-corrosion.

3 Design requirements of pressure water pipes

Pressure pipe refers to the outlet pipe between the water pump and the water storage building, which is an important factor to ensure the normal operation of the water pump. Pressurized pumping stations and irrigation high-lift pumping stations generally exceed the scope of normal water pipes, making pressurized water pipes account for a large proportion of the total investment cost of pumping stations. For the normal operation of the pumping station, the length and diameter of the pressure pipeline have great influence on the system, especially the surge pressure in the pressure pipeline will even bring fatal influence to the pumping station, so it is necessary to strengthen the design of the pressure pipeline for high-lift pumping stations and pressure pumping stations.

3. 1 Requirements for pressure water pipeline

(1) Ensure the strength of the pipeline itself and its joints, and ensure reliable sealing performance;

(2) ensure the minimum energy consumption and investment caused by pressure pipeline;

(3) Ensure the stability of the pressure water pipeline during the normal operation of the pumping station;

(4) In the process of filling or emptying the pipeline, ensure that the medium can freely enter and exit the pressure water pipeline;

(5) Ensure the safety of the pump room after the pipeline suddenly breaks;

(6) The pipeline can be emptied during maintenance to ensure the smooth maintenance.

3.2 Material selection of pressure pipeline

(1) The water circulation pressure loss of the pressure pipeline is small and the energy consumption is low, which ensures that the water pump can operate according to the standard working conditions under various working conditions and reduces the maintenance cost of the pressure pipeline;

(2) Meet the different water requirements of the pumping station and ensure that the corresponding design flow can be passed under different water pipe pressures;

(3) Ensure that the pipeline can run independently in harsh environment without displacement change, water hammer damage and slippage;

(4) Water pipe materials should be convenient for transportation, maintenance, installation, maintenance and management to ensure the smooth maintenance of pressure water pipes;

(5) Save steel, cement, wood and other materials to ensure the lowest investment cost of the whole project.

3.3 Installation of pressure pipeline

(1) installation principle. Steel pipes are mostly used in pressure water pipes of pumping stations, and the following points should be paid attention to during installation: (1) When welding steel pipes, pay attention to whether the sealing performance of welding is reliable, and polish the weld with an angle grinder after welding. (2) The gradient setting of the pressure pipeline shall meet the design requirements and national standards, and ensure that the set gradient meets the use requirements. (3) The allowable deviation of coordinates and elevation, verticality error of vertical pipeline and vertical and horizontal bending error of horizontal pipeline shall meet the specification requirements. (4) When the flange is connected, the internal thread and rust on the flange cover should be removed to ensure the smoothness of the flange surface when connecting. Remove the sealing center line on the sealing coil, and adjust the position of the center line of the pipe thread flange and the center line of the pipe to ensure mutual verticality.

(2) Installation method. The installation methods of pressure pipes can be divided into radial installation, parallel installation, series installation and parallel installation. During radial installation, the center line of the pipeline decreases with the gradual deviation from the center. Parallel installation means that the center line of pressure pipeline always keeps a constant value. For the pumping station with short pipeline and low lift, the pressure pipeline is usually arranged along the direction parallel to the longitudinal axis of the pumping station chamber, thus simplifying the pipeline structure and ensuring the reliable operation of the pressure pipeline. Series installation refers to the installation of pressure pipes without buildings between adjacent pumping stations. For high-lift pumping stations, if there is no platform between pumping stations that affects the installation of pumping stations, the pressure pipeline can be connected in series with the next water pipe. Parallel installation means that multiple water pipes use one pressure pipe, which greatly reduces the use of pressure pipes and the construction cost of pumping stations, and is mostly used for the construction of pumping stations with high lift, multiple pump groups and long pipelines. However, parallel installation will increase a lot of supporting construction, and all branch pipelines will stop running when the main pipeline is overhauled.

4 Design requirements of pipeline support mode

4. 1 pier design

Pier is used to fix pressure pipeline, which can be divided into open pier and closed pier according to structural type. Open pier is easy to maintain, but because the open structure is greatly influenced by the outside world, it is easy to cause uneven stress on the pipe wall, so this structure is mostly used to fix low-load penstock. The closed pier structure is relatively simple, less affected by the outside world, but not easy to repair. Pier is a structure that relies on its own gravity to maintain its own stability, so its design requirements and contents are basically the same as other gravity structures, that is, it is necessary to calculate the anti-sliding and anti-overturning stability of pier structure and the stability of foundation in the limit state. In the actual situation, various unfavorable limit conditions generally do not occur at the same time, so the load combination of pier structure should be carried out according to the different operating conditions of the pump to ensure the strength and stability of the pier to cope with the most unfavorable situation. The normal design of the pump is to analyze the load according to the three working conditions of stable operation, normal shutdown and sudden shutdown, taking into account the temperature change and various frictional resistance, so as to ensure that the design can make the pump reach the best operating state.

4.2 Pier design

The pier bears the load in the middle of the pressure pipeline and reduces the buckling deformation of the pressure pipeline under various loads. For the pressure pipeline, in order to adapt to the intensity influence of thermal cycle stress caused by temperature change, the displacement caused by thermal stress can be offset by the free movement of the pressure pipeline on the pier along the pipe axis. The pier only bears the normal force perpendicular to the pipe axis, and the horizontal force is mainly borne by the pier.

5 conclusion

Pump is a very important equipment in the production process, which plays an important role in the development of national science and technology automation and modern industrial level. However, in the process of using the pump, due to the influence of working environment or operators, various failures will occur. When designing the pump, the factors affecting the pump operation should be considered as much as possible to avoid equipment failure and ensure the normal and stable operation of the pump.

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