Multi-stage pump selection method is a very important part in engineering design, it is directly related to the performance and efficiency of the pump. In the selection of multi-stage pump, the need to consider a variety of factors, multi-stage pump selection methods need to consider the flow, head, media properties, operating conditions, economy and reliability and other factors, only in the full analysis and evaluation of various factors, in order to select the most appropriate multi-stage pump, to ensure the smooth progress of the project.

1. Working pressure of water pump.Suction tank pressure, drain tank pressure, pressure drop in piping system (head loss). Piping system data (pipe diameter, length, type and number of pipe accessories, geometric elevation from suction tank to pressure tank, etc.). If necessary, the device characteristic curve should also be made. If necessary, the device characteristic curve should also be made.

2, must meet the use of flow and head requirements.Flow refers to the volume of liquid passing through the pump per unit time, while lift refers to the height difference that the liquid needs to overcome from the inlet to the outlet. After the flow and lift are determined, the appropriate multi-stage pump type can be selected according to the engineering requirements, I .e. the operation time point of the pump (the intersection point of the device characteristic curve and the performance curve of the pump) is required to be kept in the high-efficiency range, thus saving power and not easily damaging the parts, the selected water pump should not only be small in size, light in weight, low in cost, but also have good characteristics and high efficiency.

3. It has good anti-cavitation performance.In this way, the excavation depth of the pump house can be reduced, and the cavitation of the pump is not caused, and the operation is stable and the service life is long. According to the selected pump to build pumping station, the project investment is small, low operating costs.

4, need to consider the nature of the medium.Different media have different density, viscosity and chemical properties. These factors will affect the selection of the pump. For example, for the pump that transports corrosive media, it is necessary to choose the pump body and impeller made of corrosion-resistant materials to ensure the service life and safety of the pump. The particle diameter and content of the body contained in the medium. Characteristics of the medium: medium name, specific gravity, viscosity, corrosion, toxicity, etc. The required flow rate, the transmission medium temperature: (C). General agricultural pumps if the use of open channel water delivery, but also must consider the leakage and evaporation. Industrial pumps can ignore the leakage in the pipeline system in the process, but the impact on the flow rate must be considered when the process changes.

5. Pump operating conditions and environmental factors.Working temperature, medium temperature, altitude and other factors will affect the performance of the pump. Therefore, when selecting the type, it is necessary to refer to the performance curve and technical parameters provided by the manufacturer, and evaluate and select according to the actual situation.

6. The discharge side of the pump must be equipped with valves (ball valves or globe valves, etc.) and check valves.The valve is used to adjust the operating point of the pump. The check valve can prevent the pump from reversing when the liquid flows back, and prevent the pump from being hit by water hammer (when the liquid flows back, huge reverse pressure will be generated, which will damage the pump). The pipe layout should be arranged as straight pipe as much as possible, minimize the accessories in the pipe and minimize the length of the pipe as much as possible. When it is necessary to turn, the bending radius of the elbow should be 3~5 times of the pipe diameter, and the angle should be greater than 90 ℃ as much as possible.

7. Reasonable choice of pipe diameter.The pipe diameter is large, under the same flow rate, the liquid flow speed is small, and the resistance loss is small, but the price is high and the pipe diameter is small, which will lead to a sharp increase in the resistance loss, which will increase the head of the selected pump, increase the power of the belt, and increase the cost and operation cost. Therefore, the discharge pipe and its pipe joints should be considered from the perspective of technology and economy.

8. Economy and reliability.Selection to consider the price of the pump, maintenance costs and energy consumption and other factors to ensure that the selection of both meet the needs of the project and economic and reasonable multi-stage pump.