Traditional Culture Encyclopedia - Traditional virtues - What is the physical principle of water pump?

What is the physical principle of water pump?

According to different working principles, it can be divided into positive displacement pump and vane pump. Positive displacement pumps use the change of working chamber volume to transfer energy, mainly including piston pump, piston pump, gear pump, diaphragm pump and screw pump. Vane pumps use the interaction between rotating blades and water to transfer energy, including centrifugal pumps, axial pumps and mixed-flow pumps. The pump body of submersible pump is vane pump. Other types of water pumps include jet pump, water hammer pump and internal combustion pump. It works by jet water hammer and fuel deflagration principle respectively. Hydraulic pump is a combination of hydraulic turbine and vane pump. Among the above pumps, the following are more representative. Centrifugal pump is a kind of pump that uses centrifugal force to increase water pressure and make it flow. It consists of pump shell, impeller, rotating shaft, etc. The power machine drives the rotating shaft, which drives the impeller to rotate at high speed in the pump shell, and the water in the pump is forced to produce centrifugal force with the rotation of the impeller. Centrifugal force forces the liquid to be thrown out from the periphery of the impeller, and merges into a high-speed and high-pressure water flow to be discharged from the pump through the pump casing, forming a low pressure in the center of the impeller, thus sucking in new water flow and forming a continuous water flow conveying function. Impeller has blades bent in the opposite direction of rotation, and its structural types are closed, semi-closed and open. Most agricultural impellers are closed, and both sides of the blades are closed by disks. The pump body gradually expands into a volute shape along the direction of the water outlet pipe. Absorbing water from one side of the impeller is called a single suction centrifugal pump, and absorbing water from both sides of the impeller is called a double suction centrifugal pump. In order to increase the lift, multiple impellers can be installed on the same shaft to form a multistage centrifugal pump. The water discharged from the former impeller enters the water inlet of the latter impeller and is discharged from the latter impeller after being pressurized, so the more impellers, the higher the pressure. Some centrifugal pumps have devices that automatically remove air from the suction pipe and pump body. They are called self-priming centrifugal pumps, and there is no need to inject water into the pump body before starting, but their efficiency is often lower than that of ordinary centrifugal pumps. Centrifugal pumps are widely used in farmland irrigation and drainage and water supply for agriculture and animal husbandry. It is mostly used in occasions with high lift and small flow. The head of single-stage centrifugal pump is 5 ~ 125m, and the discharge flow is uniform, generally 6.3 ~ 400 m3/ hour, and the efficiency can reach about 86 ~ 94%. Axial flow pump consists of pump shell, impeller and rotating shaft. Also known as propeller pump. There are several propeller-shaped blades on the impeller. When the power machine drives the impeller to rotate with the rotating shaft, each blade pushes the water to one end and absorbs water from the water source at the other end, so that the water flows continuously in the direction parallel to the rotating shaft, thus achieving the purpose of continuously conveying water. The rotation of the impeller increases the pressure of the water flow. After the rotating water flow from the impeller passes through the fixed guide vanes, the rotating speed is eliminated, and part of its kinetic energy is converted into pressure energy due to diffusion, which pushes the water flow in the pump casing to rise along the axial direction and flow out of the water outlet pipe. Axial flow pumps are mostly used in situations with low lift and large flow, and the lift range is about 1 ~ 25m. The flow rate is 2.7 ~ 60.0 m3/s and the efficiency can reach 85 ~ 90.5%. There are three installation methods: vertical, horizontal and inclined, among which vertical axial flow pump is widely used (Figure 2). The installation angle of propeller blades on the impeller hub of large-scale axial-flow pump can be adjusted, or it can be adjusted with time by the hydraulic transmission shaft in operation to meet the requirements of the change of head and flow rate and obtain higher productivity, so it is called adjustable axial-flow pump. Tubular pump is a kind of horizontal axial pump. It consists of a motor, a deceleration device and a water pump, and is installed in the machine pit inside the underwater dam. Its water inlet and outlet channel is located in a straight line, which is approximately cylindrical, with small hydraulic loss, high pumping efficiency, compact structure, convenient installation and maintenance, and simple pumping station project. Masonry pump is a low-lift axial-flow pump. Except the impeller and the pump casing around it are made of metal, the water inlet channel and the water outlet channel are of masonry or concrete structure, with a head below 2m, large flow, simple structure, low cost and high efficiency. Suitable for drainage irrigation in low-lying areas. Mixed-flow pump is a kind of water pump with the characteristics of centrifugal pump and axial flow pump in structure and working principle. When the impeller is driven by the power machine to rotate, the blades push the water body on the one hand, and at the same time drive the water body to rotate to produce centrifugal effect. Water flows under the thrust and centrifugal force of blades and increases the pressure. Water flows into the impeller from the axial direction and then flows out obliquely along the blades, which is often used in occasions with large conveying displacement and medium pressure. There are usually two types: volute type and guide vane type. The structure of volute mixed-flow pump is similar to centrifugal pump, and the kinetic energy obtained by water flowing through the impeller is converted into pressure energy by using volute-shaped flow channel. Small and medium-sized mixed-flow pumps generally adopt volute structure. Guide vane mixed-flow pump, also known as diagonal flow pump, is similar to axial flow pump in structure, with the characteristics of small radial size and simple and light structure. Large mixed-flow pumps are mostly guide vanes, and the installation angle of their vanes can generally be adjusted. The lift range of mixed-flow pump is generally 3 ~ 10.5m, the starting power is low, and it can adapt to the change of water level, and the flow rate is 0.1~ 50m3/s; The efficiency can reach 64 ~ 86%. Since 1970s, large-scale mixed-flow pump has developed rapidly, and it tends to replace large-scale axial-flow pump on many occasions. Long-axis deep well pumps are mostly vertical single-suction centrifugal pumps, and their impellers are installed below the dynamic water level in the well. The power machine is installed on the well and drives the impeller to rotate in the diversion shell by driving the long shaft. Water flows up to the ground through the water pipe along the flow channel between the guide shell and the impeller. When the lift is high, a multi-stage centrifugal pump with multiple impellers in series can be used. Because the manufacturing and installation accuracy of transmission shaft is high, and the efficiency decreases significantly with the increase of well depth, it is generally only used in deep wells with well depth less than 100 meters. The impeller of the submersible pump body and the motor driving the impeller are immersed in the water to work. There are two kinds of pumps, one for deep wells and the other for working faces. Submersible pump for deep well supplies power to motor through cable extending into the well, which saves long shaft drive, so it has compact structure, light weight and convenient installation, use and transfer. It tends to replace long-axis deep well pumps in areas with power supply, but it is not suitable for wells with high sediment concentration and areas without power supply. The motors used in submersible pumps are dry (all motors are sealed), semi-dry (the stator of the motor is sealed and the rotor runs in water), oil-filled (the motor is filled with oil to prevent moisture from invading the windings) and wet (the motor is filled with water and the stator and rotor run in water). The first three types all need to be sealed, which requires high manufacturing and installation accuracy. Therefore, agricultural deep well submersible pump usually adopts wet motor, and its stator winding adopts water-resistant insulated wire or casting synthetic resin at the end and slot of stator winding. The water entering the motor has little influence, and the sealing structure can be greatly simplified, only sand control is needed. Some submersible pumps in deep wells have a lift as high as 65,438+0,400 meters and a maximum flow rate of 65,438+0.4 cubic meters per second. Jet deep well pumps are usually composed of jet pumps, centrifugal pumps and corresponding housings. Used for pumping water from deep wells within 30 meters. The working principle of jet pump is to make the pressure spray to the throat inlet through the nozzle. Due to the lateral turbulent diffusion of the jet, the air in the suction pipe is taken away and a vacuum is formed in the pipe. Well water is sucked up and mixed with the jet water at the throat for energy exchange. At the outlet of the throat, the velocity of the two approaches to the same, and then most of the kinetic energy is converted into pressure energy through the diffusion pipe, which further increases the water pressure and finally discharges it from the drainage pipe. There are two kinds of jet deep well pumps: ① Jet pumps are connected in parallel with centrifugal pumps, which send pressurized water into the jet pumps through pipelines, and the jet pumps lift the water together with the absorbed water, so that low-flow high-pressure water can be converted into high-flow low-pressure water, which is mainly used for ground irrigation and channel dredging; (2) A jet pump and a centrifugal pump are connected in series and parallel, so that the jet pump pressurizes the centrifugal pump to improve its water absorption range. Part of the effluent from the centrifugal pump is provided to the jet pump, and the rest is sent to the pressure tank or pressure pipeline. The effluent pressure is high, and it is mainly used for sprinkler irrigation equipment and water supply for agriculture and animal husbandry. Compared with submersible pump and long shaft deep well pump, jet deep well pump has the characteristics of simple structure, reliable work, convenient manufacture and low cost. But the efficiency is low and the power consumption is high under the same working conditions. Screw pump is a positive displacement pump, which sucks and transports water depending on the change of pump cavity volume when the screw rotates. There are single screw, twin screw and multi-screw types. Single screw pump is used in agriculture, and its pump cavity consists of steel screw and rubber sleeve fixedly installed in the pump shell. The single-pitch screw rotates in the sleeve with double-pitch internal thread, and the cavity formed between them moves from the suction end to the outlet end, thus forming a continuous water flow. Because of its simple structure, small size, convenient disassembly, reliable operation and good self-priming performance, it is mostly used in mobile sprinkler irrigation system. Manual diaphragm pump is used for low-lift and small-flow water lifting operation, which consists of pump body, water inlet and outlet pipes, water inlet and outlet valves, diaphragm and push-pull rod. 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 arranged outside two separate pump chambers. When working, two people operate the push-pull rod connected with the diaphragm by hand to push the diaphragm to do reciprocating motion of squeezing and opening, so that the volumes of the two pump chambers alternately expand and shrink. When the pump cavity expands, the pressure decreases, the water inlet valve opens, the water outlet valve closes, and water flows into the pump cavity from the water inlet pipe; When the pump cavity contracts, the pressure increases, the water inlet valve closes, the water outlet valve opens, and the water in the pump cavity flows out from the drain pipe. The two pump chambers alternately absorb water and drain water, and can lift water 10 ~ 20 tons per hour. Rod piston pump is driven by animal prime mover, wind turbine or internal combustion engine. , often used to pump water from a well in a pasture. It consists of a pump barrel, a piston, a water inlet and outlet pipe, a water inlet and outlet valve, a pull rod and a transmission device. The piston is driven by the pull rod connected with it and reciprocates up and down in the pump cylinder. When the piston moves upward, the water inlet valve opens, and the water in the water inlet pipe enters the pump barrel, while the water outlet valve closes, so that the water on the piston is driven upward; When the piston moves downward, the water inlet valve is closed and the water outlet valve is opened, and the water in the pump cylinder rises from the water outlet valve to the piston, so that the water is continuously discharged from the drain pipe.