The impeller of the pump body and the motor driving the impeller are submerged into the water to work. There are two kinds of pumps for deep wells and working surfaces. The submersible electric pump for deep well supplies power to the motor through the cable extending into the well, eliminating the need for a long drive shaft, so it is compact in structure, light in weight, easy to install, use and transfer, and has a tendency to replace the long shaft deep well pump in areas with power supply, but It is not suitable for wells with high sand content and areas without power supply. The motors used in submersible pumps are dry type (the motor is completely sealed), semi-dry type (the stator of the motor is sealed, and the rotor runs in water), oil-filled type (the motor is filled with oil to prevent moisture from entering the winding) and wet type (the inside of the motor water-filled, both the stator and the rotor operate in water) and other types. The first three types all need to be sealed and require high manufacturing and installation accuracy. Therefore, the agricultural deep well submersible electric pump usually adopts a wet motor, and its stator winding uses water-resistant insulated wires or pours synthetic resin at the end of the stator winding and in the slot. Small, the sealing structure can be greatly simplified, only sand control is required. Some deep well submersible electric pumps have a lift of up to 1400 meters and a maximum flow of 1.4 m3/s.

　　A centrifugal pump is a pump that uses centrifugal force to increase the pressure of water and make it flow. It consists of pump casing, impeller, shaft and so on. The power machine drives the rotating shaft, and the rotating shaft drives the impeller to rotate at high speed in the pump casing, and the water body in the pump is forced to rotate with the impeller to generate centrifugal force. The centrifugal force forces the liquid to be ejected from the periphery of the impeller, and then merged into high-speed and high-pressure water to flow out of the pump through the pump casing. The center of the impeller forms a low pressure, thereby sucking in new water flow and forming a continuous water flow delivery. The impeller has blades that are curved against the direction of rotation. There are three types of structure: closed, semi-closed and open. Most agricultural impellers are closed impellers, and the blades are closed by discs on both sides. The pump body gradually expands into a volute shape along the direction of the outlet pipe. The water flow sucked from one side of the impeller is called single-suction centrifugal pump, and the water sucked from both sides of the impeller is called double-suction centrifugal pump. In order to increase the head, multiple impellers can be installed on the same shaft to become a multistage centrifugal pump. The water discharged from the previous impeller enters the water inlet of the latter impeller, and is discharged from the latter impeller after being pressurized. Therefore, the more impellers there are, the higher the pressure will be. Some centrifugal pumps are equipped with a device that can automatically remove the suction pipe and the air in the pump body. There is no need to fill the pump body with water before starting. They are called self-priming centrifugal pumps, but their efficiency is often lower than that of ordinary centrifugal pumps.

　　Centrifugal pumps are the most widely used in irrigation and drainage of farmland and water supply for agriculture and animal husbandry. It is mostly used in occasions with high head and small flow. The head of the single-stage centrifugal pump is 5-125 meters, the discharge flow is uniform, generally 6.3-400 m3/hour, and the efficiency can reach about 86-94%.

　　Axial flow pumps consist of pump casings, impellers and shafts. Also called propeller pump. There are several propeller-shaped blades on the impeller. When the impeller is driven and rotated by the power machine together with the rotating shaft, each blade pushes the water to one end, and at the same time absorbs water from the water source at the other end, so that the water generates a continuous flow along the direction parallel to the rotating shaft. Flow, to achieve the purpose of continuously transporting water. The pressure of the water flow increases due to the rotation of the impeller. After the rotating water flow from the impeller passes through the fixed guide vane, the partial velocity of rotation is eliminated, and part of the kinetic energy is converted into pressure energy due to diffusion, which pushes the water flow in the pump casing to rise in the axial direction and flows out from the outlet pipe. Axial flow pumps are mostly used in occasions with low head and large flow, the head range is about 1-25 meters; the flow rate is 2.7-60.0 m3/s, and the efficiency can reach 85-90.5%. There are three types of installation methods: vertical, horizontal and inclined, among which vertical axial flow pumps are used more (Figure 2). The installation angle of the propeller blades on the impeller hub of a large axial flow pump can be adjusted, or the hydraulically driven shaft can be adjusted over time during operation to meet the requirements of head and flow changes and obtain higher productivity, so it is called adjustable shaft. flow pump.

　　Jet-type deep well pumps are usually composed of jet pumps and centrifugal pumps with corresponding casings. Used to extract water from deep wells within 30 meters. The working principle of the jet pump is to make the pressure spray to the entrance of the throat through the nozzle. Due to the lateral turbulent diffusion of the jet, the air in the suction pipe is taken away to form a vacuum in the pipe, and the well water is sucked into the throat with the jet water. Mixing, energy exchange. At the outlet of the throat pipe, the flow velocity of the two approaches the same, and then most of the kinetic energy is converted into pressure energy through the diffusion pipe, so that the water pressure is further increased, and finally discharged from the drain pipe.

　　There are two combination types of jet-type deep well pumps: ①The jet pump is connected in parallel with the centrifugal pump, and the centrifugal pump sends pressure water into the jet pump through the pipeline, and the jet pump lifts this part of water upward together with the absorbed water, so that the small flow High-pressure water is converted into high-flow low-pressure water, which is mainly used for ground irrigation and channel dredging; ②The jet pump and centrifugal pump are connected in series and parallel, so that the jet pump can pressurize the centrifugal pump to increase its suction, and the centrifugal pump Part of the water output is provided to the jet pump, and the rest is sent to the pressure pool or pressure pipeline. The water output pressure is relatively high, and it is mainly used for sprinkler irrigation equipment and water supply for agriculture and animal husbandry. Compared with submersible electric pumps and long-axis deep well pumps, jet-type deep well pumps have the characteristics of simple structure, reliable operation, convenient manufacture, and low cost; but they have lower efficiency and higher power consumption under the same working conditions.

　　The screw pump is a volumetric pump that sucks and delivers water by changing the volume of the pump cavity when the screw rotates. There are single-screw, twin-screw and multi-screw types. What is used in agriculture is a single screw pump, the pump chamber of which is composed of a steel screw and a rubber sleeve fixedly installed in the pump casing. The single-pitch screw rotates in the double-pitch inner helix casing, and the cavity formed between the two moves from the suction end to the outlet end, thereby forming a continuous water flow. Because of its simple structure, small size, easy disassembly, reliable operation, and good self-priming performance, it is mostly used in mobile sprinkler irrigation systems.

　　The manual diaphragm pump is used for low-lift and small-flow water lifting operations. It consists of a pump body, water inlet and outlet pipes, water inlet and outlet valves, diaphragms, and push-pull rods. The pump body can be composed of one or two pump chambers. For a diaphragm pump with two pump chambers, the diaphragm is arranged in the center of the pump body, or the two diaphragms are respectively installed outside the two separated pump chambers. When working, two people operate the push-pull rod connected with the diaphragm by hand, and push the diaphragm to make a reciprocating movement of pressing and opening, so that the volume of the two pump chambers expands and shrinks alternately. When the pump chamber expands, the pressure decreases, the water inlet valve opens and the outlet valve closes, and water flows into the pump chamber from the inlet pipe; when the pump chamber shrinks, the pressure increases, the water inlet valve closes, the outlet valve opens, and the water in the pump chamber The water flows out from the drainage pipe, and the two pump chambers absorb and drain water alternately, and can lift 10-20 tons of water per hour.

　　The matching power of the water pump The reasonable matching of the water pump and the power is of great significance to ensure the normal operation of the water pump to obtain high efficiency and low energy consumption. The power of the supporting power machine is calculated according to the head H (m) and flow Q (m3/s) of the pump according to the following formula: (kW). Head H is composed of geometric head Hj and pipeline loss HS, which can be estimated according to HS=(0.1～0.2)Hj during preliminary selection. After the pipeline is determined, according to the type or size of the pipeline and joints, it is calculated by the method of fluid mechanics or obtained by looking up the table. In the formula, K is the power reserve coefficient, commonly used K=1.05～1.3, take a small value when the power is large; η1 is the transmission efficiency, when the power machine is directly connected with the water pump, η1=1; η2 is the efficiency of the water pump, determined according to the pump type and working conditions .

　　The diameter D of the water inlet and outlet pipes matching the pool water pump is selected according to the following formula: D=1.13Q1/2V-1/2 (m), where V is the flow rate in the pipe, and the general water inlet pipe V ≤ 2 m/s, the outlet pipe V ≤ 3 m/s. If a gradient tube with varying diameter is used, the length of the gradient part should be 5 to 7 times greater than the average diameter. The water inlet of the centrifugal pump and the axial flow pump is set at a distance h1 below the water surface of the water inlet pool, h1=(1.4～1.6)D1, and D1 is the diameter of the water inlet pipe. The centerline of the impeller of the axial flow pump is set at a distance h3 below the water surface of the inlet pool, h2≥(0.75～D)D0, where D0 is the diameter of the impeller. The height h0=(0.5～1)D0 of the inlet pipe from the bottom of the pool. The width of the inlet pool of a single water pump is (2~3)D1. In the water inlet pool where multiple water pumps are installed, the distance between adjacent water inlet pipes is (3~3.5)D1. The distance from the water inlet pipe to the rear wall of the water inlet pool is (1~1.5)D1. In order to avoid wasting head, the outlet pipe is usually installed below the water surface of the outlet pool. The distance from the lower edge of the outlet pipe of the small and medium-sized water pump to the bottom of the pool is about 10-20 cm; the vertical distance from the upper edge of the outlet pipe to the water surface is (1-2) V?/2g, and v2 is the outlet flow rate (m/s); The length of the pool is (6～12)D2. D2 is the diameter of the outlet pipe; the distance between the outlet pipe and the pool wall is 0.2 to 0.5 meters.

　　Development trend The requirements for the development of agricultural water pumps are to improve efficiency, reduce energy consumption and make full use of natural energy. Replacing many small pumps with one large pump can improve unit efficiency, save materials, reduce energy consumption and project cost, and facilitate automatic management. Therefore, various large-scale axial flow pumps and mixed flow pumps have developed rapidly, with the largest impeller diameters reaching 4.6 meters and 6.2 meters respectively, and the maximum supporting power reaching 12,500 kilowatts. Mixed flow pumps have replaced some high-lift axial flow pumps and low-lift centrifugal pumps. trend. In terms of deep well water extraction, submersible electric pumps are mainly developed, and their diameters have reached 1 meter. Some use 6000-volt high-voltage motors with a maximum power of 2500 kilowatts. Water wheel pumps, wind rod pumps, screw pumps, diaphragm pumps driven by various human and animal power, piston pumps and water pumps specially used for supporting sprinkler irrigation equipment have also received varying degrees of attention in China and some other countries.