Function of the pump:
1. A pump is a device that transports liquid substances from a lower level to a higher level. It has a water suction port and a pressure water port. The water suction port sucks liquid into the pump body, and through the high-speed operation of the impeller, the mechanical energy is converted into kinetic energy and potential energy of the liquid. Press the liquid out from the water pressure port. Therefore, the pump needs to pump the medium first and then provide pressure to the medium. The two are combined into one to form the pump.
2. Lift is the height to which the pump can deliver liquid. Of course, this statement is somewhat one-sided, but it can be understood simply this way. Lift should be the potential energy converted from the mechanical energy of the pump impeller to the liquid.
3. Pumps can be used wherever liquid needs to be transported from a low level to a high level. There are many types of pumps, and there are different pumps for transporting liquids with different media.
The pumps in the power station are mainly used to transport power plant wastewater. To drain away wastewater or perform wastewater treatment, a pump is required.
A pump is a machine that transports liquid or pressurizes liquid. It transfers the mechanical energy of the prime mover or other external energy to the liquid, increasing the energy of the liquid. The pump is mainly used to transport liquids including water, oil, acid and alkali liquids, emulsions, suspoemulsions and liquid metals. It can also transport liquids, gas mixtures and liquids containing suspended solids.
A pump in a broad sense is a machine that transports fluid or pressurizes it, including some machines that transport gas. The pump transfers the mechanical energy of the prime mover or the energy of other energy sources to the liquid, thereby increasing the energy of the liquid.
The improvement of water is very important for human life and production. There were various water-lifting devices in ancient times, such as the Egyptian chain pump (17th century BC), the Chinese tangerine (17th century BC), the windlass (11th century BC), the waterwheel (1st century AD), and the 3rd century BC The screw rod invented by Archimedes in ancient Greece. Around 200 BC, the ancient Greek craftsman Ctesibius invented the most primitive piston pump fire extinguishing pump. As early as 1588, there were records of a 4-blade sliding vane pump, and various other rotary pumps appeared one after another. In 1689, D. Papin of France invented the volute centrifugal pump with a 4-blade impeller. In 1818, a centrifugal pump with radial straight blades, semi-open double-suction impeller and volute appeared in the United States. From 1840 to 1850, H.R. Worthington of the United States invented a piston pump with direct steam action in which the pump cylinder and the steam cylinder faced each other, marking the formation of the modern piston pump. From 1851 to 1875, multi-stage centrifugal pumps with guide vanes were invented one after another, making it possible to develop high-lift centrifugal pumps. Subsequently, various pumps came out one after another. With the application of various advanced technologies, the efficiency of pumps has gradually improved, and the performance range and applications have also expanded.
There are many types of pumps, which can be divided according to their working principles: ① Power pumps, also called impeller pumps or vane pumps, rely on the dynamic effect of the rotating impeller on the liquid to continuously transfer energy to The liquid increases the kinetic energy (mainly) and pressure energy of the liquid, and then converts the kinetic energy into pressure energy through the extrusion chamber. It can be divided into centrifugal pumps, axial flow pumps, partial flow pumps and vortex pumps, etc. ② Positive displacement pumps rely on periodic changes in the volume of the sealed working space containing the liquid to periodically transfer energy to the liquid, increasing the pressure of the liquid to the point where the liquid is forcibly discharged. According to the movement form of the working components, it can be divided into reciprocating pumps and rotary pumps. ③Other types of pumps transmit energy in other forms. For example, a jet pump relies on high-speed injection of working fluid to suck the fluid to be transported into the pump and mix it to exchange momentum to transfer energy; a water hammer pump uses part of the flowing water to be raised to a certain height during braking to transfer energy; an electromagnetic pump uses The energized liquid metal flows under the action of electromagnetic force to achieve transportation. In addition, pumps can also be classified according to the nature of the liquid transported, driving method, structure, use, etc.
The improvement of water is very important for human life and production. There have been various water-lifting devices in ancient times, such as the Egyptian chain pump (17th century BC), the Chinese tangerine (17th century BC), the windlass (11th century BC) and the waterwheel (1st century AD).
The more famous one is the screw rod invented by Archimedes in the third century BC, which can smoothly and continuously lift water to a height of several meters. Its principle is still used by modern screw pumps.
The fire extinguishing pump invented by the ancient Greek craftsman Ctesibius around 200 BC is the most primitive piston pump. It already has the main components of a typical piston pump, but the piston pump is only emerging. It developed rapidly after the invention of the steam engine.
From 1840 to 1850, Worthington in the United States invented a piston pump in which the pump cylinder and the steam cylinder were opposite and the steam acted directly, marking the formation of the modern piston pump. The 19th century was the climax of the development of piston pumps, which were used in various machinery such as hydraulic presses. However, with the sharp increase in water demand, starting in the 1920s, low-speed piston pumps with greatly restricted flow rates were gradually replaced by high-speed centrifugal pumps and rotary pumps. However, reciprocating pumps still occupy a dominant position in the field of high pressure and small flow. In particular, diaphragm pumps and plunger pumps have unique advantages and are increasingly used.
The emergence of rotary pumps is related to the increasingly diverse industrial requirements for liquid transportation. As early as 1588, there were records of a four-blade sliding vane pump. After that, various other rotary pumps appeared one after another. However, until the 19th century, rotary pumps still had shortcomings such as large leakage, large wear and low efficiency. At the beginning of the 20th century, people solved the problems of rotor lubrication and sealing, and adopted high-speed motor drive. Only then did rotary pumps suitable for higher pressures, small and medium flow rates, and various viscous liquids develop rapidly. The types of rotary pumps and the types of liquids suitable for conveying are unparalleled by other types of pumps.
The idea of ??using centrifugal force to transport water first appeared in sketches by Leonardo da Vinci. In 1689, French physicist Papin invented the four-blade impeller volute centrifugal pump. But what is closer to the modern centrifugal pump is the so-called Massachusetts pump with radial straight blades, semi-open double-suction impeller and volute that appeared in the United States in 1818. From 1851 to 1875, multi-stage centrifugal pumps with guide vanes were invented one after another, making it possible to develop high-lift centrifugal pumps.
Although as early as 1754, Swiss mathematician Euler proposed the basic equation of impeller hydraulic machinery and laid the theoretical foundation for centrifugal pump design, it was not until the end of the 19th century that the invention of high-speed electric motors made centrifugal pumps Only after obtaining the ideal power source can its advantages be fully exerted. On the basis of the theoretical research and practice of many scholars such as Renault in the UK and Pfludreyer in Germany, the efficiency of the centrifugal pump has been greatly improved, and its performance range and application fields have also been increasingly expanded, and it has become the most widely used modern pump. Highest output pump.
Pumps are usually divided into positive displacement pumps, dynamic pumps and other types of pumps according to their working principles, such as jet pumps, water hammer pumps, electromagnetic pumps, and gas lift pumps. In addition to being classified according to their working principles, pumps can also be classified and named according to other methods. For example, according to the driving method, it can be divided into electric pumps and water wheel pumps; according to the structure, it can be divided into single-stage pumps and multi-stage pumps; according to the purpose, it can be divided into boiler feed pumps and metering pumps; according to the properties of the transported liquid, it can be divided into Water pumps, oil pumps and mud pumps, etc.
Positive displacement pumps rely on the reciprocating or rotary motion of the working element in the pump cylinder to alternately increase and decrease the working volume to achieve the suction and discharge of liquid. Positive displacement pumps whose working components make reciprocating motion are called reciprocating pumps, and those which make rotary motion are called rotary pumps. The suction and discharge processes of the former are carried out alternately in the same pump cylinder and are controlled by the suction valve and the discharge valve; the latter forces the liquid from the suction through the rotation of working components such as gears, screws, leaf-shaped rotors or slides. side transferred to the discharge side.
The flow rate of a positive displacement pump is constant at a certain speed or number of reciprocations and hardly changes with the pressure; the flow rate and pressure of a reciprocating pump have large pulsations, and corresponding pulsation reduction measures need to be taken; rotary pumps Generally there is no pulsation or only small pulsation; it has self-priming ability, and it can remove the air in the pipeline and suck in the liquid after the pump is started; the discharge pipeline valve must be fully opened when starting the pump; the reciprocating pump is suitable for high pressure and small flow rate ; Rotary pumps are suitable for small and medium flow rates and higher pressures; reciprocating pumps are suitable for transporting clean liquids or gas-liquid mixtures. In general, positive displacement pumps are more efficient than dynamic pumps.
⑦Suitable for transporting clean liquids with very low viscosity (such as clean water). Specially designed pumps can transport mud, sewage, etc. or solid objects through water. Power pumps are mainly used for water supply, drainage, irrigation, process liquid transportation, power station energy storage, hydraulic transmission and ship jet propulsion.
The main characteristics of positive displacement pumps are: ① The flow rate of a certain pump at a certain rotation speed or number of reciprocations is certain, and it hardly changes with the pressure. The operating point pressure and shaft power depend on the conditions of the device system connected to the pump. Therefore, when the pump operates with a blocked discharge pipe (equivalent to infinite system resistance), its pressure and shaft power will increase to the point where the pump Or the prime mover is damaged, so a safety valve must be installed to protect the pump (except for pumps driven by steam directly or compressed air). ② The flow and pressure of the reciprocating pump have large pulsations, and corresponding pulsation reduction measures need to be taken; rotary pumps generally have no pulsation or only small pulsations. ③ It has self-priming ability. After the pump is started, it can remove the air in the pipeline and suck in the liquid. ④When starting the pump, the discharge pipe valve must be fully opened. ⑤ The reciprocating pump is a low-speed machine with large size and high manufacturing and installation costs; the rotary pump has a higher speed, up to 3000 rpm. ⑥Reciprocating pumps are suitable for high pressures (up to 350 MPa) and small flows (below 100 m3/h); rotary pumps are suitable for small and medium flow rates (below 400 m3/h) and high pressures (below 35 MPa). ). Generally speaking, the efficiency of positive displacement pumps is higher than that of dynamic pumps, and the high efficiency area of ??the efficiency curve is wider. The efficiency of reciprocating pumps is generally 70 to 85%, and can reach more than 90%. ⑦Reciprocating pumps are suitable for transporting clean liquid or gas-liquid mixtures. Some pumps such as diaphragm pumps can transport mud, sewage, etc. They are mainly used for water supply, high-pressure liquid source and metering transportation. Rotary pumps are suitable for transporting lubricating clean liquids and liquid-gas mixtures, especially liquids with high viscosity. They are mainly used for the transportation of oil and food liquids and hydraulic transmission.
The working principle of the centrifugal pump
The impeller is installed in the pump casing and fastened to the pump shaft 3. The pump shaft is directly driven by the motor. There is a liquid suction 4 connected to the suction pipe 5 in the center of the pump casing. The liquid enters the pump through the bottom valve 6 and the suction pipe. The liquid discharge port 8 on the pump housing is connected to the discharge pipe 9.
Before the pump starts, the pump casing is filled with the liquid to be transported; after starting, the impeller is driven by the shaft to rotate at high speed, and the liquid between the blades must also rotate with it. Under the action of centrifugal force, the liquid is thrown from the center of the impeller to the outer edge and gains energy, leaving the outer edge of the impeller at high speed and entering the volute pump casing. In the volute, the liquid decelerates due to the gradual expansion of the flow channel, and converts part of the kinetic energy into static pressure energy. Finally, it flows into the discharge pipe at a higher pressure and is sent to the required location. When the liquid flows from the center of the impeller to the outer edge, a certain vacuum is formed in the center of the impeller. Since the pressure above the liquid level in the storage tank is greater than the pressure at the pump inlet, the liquid is continuously pressed into the impeller. It can be seen that as long as the impeller continues to rotate, liquid will continue to be sucked in and discharged.