Pumps are machines that transport liquid or pressurize liquid. It transfers the mechanical energy of the prime mover or other external energy to the fluid, increasing the fluid's energy. Pumps are mainly used to deliver liquids including water, oils, acids and bases, emulsions, suspoemulsions, and liquid metals, as well as liquids, gas mixtures and liquids containing suspended solids. Water lifting is very important for human life and production. In ancient times there were various kinds of water-lifting appliances such as chain pumps in Egypt (17th century BC), tangerines in China (17th century BC), pots and lanterns (11th century BC) and water tankers (1st century AD). More famous also the third century BC, Archimedes invented the spiral rod, the water can be smooth and continuous to a few meters high, the principle is still used by modern screw pump. Around 200 BC, the fire pump invented by the ancient Greek craftsman Kate Sibius was one of the most primitive piston pumps that already had the main components of a typical piston pump, but the piston pump developed rapidly only after the steam engine appeared . 1840 ~ 1850, the United States invented the Worthington pump and the cylinder opposite the direct effect of steam piston pump, marking the formation of the modern piston pump. The 19th century was the climax of piston pump development, when it was used in hydraulic presses and other machines. However, with the rapid increase in water demand, low-speed, heavily-restricted piston pumps have been gradually replaced by high-speed centrifugal and rotary pumps since the 1920s. However, the reciprocating pump still occupies a major position in the field of high pressure and small flow, especially the diaphragm pump and the plunger pump have their unique advantages and their applications are increasing day by day. The emergence of rotary pumps has been associated with the increasing diversification of industrial requirements for liquid transport. As early as 1588, there was a record about the four-blade vane pump, and various other rotary pumps appeared one after another. However, until the 19th century, the rotary pump still had the disadvantages of large leakage, large wear and low efficiency. At the beginning of the 20th century, people solved the problem of rotor lubrication and sealing, and they were driven by high-speed motors. The rotary pumps suitable for higher pressure, medium and small flow rates and various viscous liquids developed rapidly. Rotary pump type and suitable for the type of liquid as many other types of pumps less than. The idea of ​​using centrifugal force to feed water first appeared in the sketches made by Leonardo da Vinci. In 1689, the French physicist Papan invented a four-bladed impeller volute centrifugal pump. But closer to modern centrifugal pumps are the so-called Massachusetts pumps with radial straight blades, half-open double-suction impellers and volutes appearing in the United States in 1818. From 1851 to 1875, multistage centrifugal pumps with vanes were invented one after the other, making it possible to develop high-lift centrifugal pumps. The basic formula of the impeller hydraulic machinery was put forward and laid the theoretical foundation of centrifugal pump design. However, it was not until the late 19th century that the invention of a high-speed motor made the centrifugal pump obtain the ideal power source and its superiority was fully utilized. Based on the theoretical research and practice of many scholars such as Reynolds in Britain and Pfrederreich in Germany, the efficiency of centrifugal pumps has been greatly improved. Its performance range and application area have also been expanding. It has become the most widely used, The largest pump output. Pumps are usually divided by the principle of positive displacement pumps, power pumps and other types of pumps, such as jet pump, water hammer pump, electromagnetic pump, gas lift pump. In addition to the principle of pump classification, but also by other methods of classification and naming. For example, according to the driving method can be divided into electric pump and water pump; according to the structure can be divided into single-stage pump and multi-stage pump; According to the use can be divided into boiler feed pump and metering pump; According to the nature of liquid can be divided into Pumps, pumps and mud pumps. Positive displacement pump is to rely on working elements in the pump cylinder for reciprocating or rotary motion, so that work volume alternately increase and decrease, in order to achieve liquid inhalation and discharge. The reciprocating motion of the working elements of the positive displacement pump called the reciprocating pump, known as rotary motion rotary pump. The former suction and discharge process alternately in the same pump cylinder, and by the suction valve and the discharge valve to control; the latter through the gears, screws, leaf rotors or vanes and other working elements of the rotation, forcing liquid from the inhalation Side to the discharge side. Volumetric pump at a certain speed or reciprocating frequency of the flow is certain, almost no change with the pressure; reciprocating pump flow and pressure pulsation, the need to take appropriate measures to reduce pulsation; rotary pump generally no pulsation or only a small Pulsation; with self-suction capacity, the pump can be started immediately after the suction of liquid in the suction pipe; start the pump must be completely open the discharge pipe valve; reciprocating pump for high pressure and low flow; rotary pump for small and medium-sized flow And higher pressure; reciprocating pump suitable for conveying clean liquid or gas-liquid mixture. In general, positive displacement pumps are more efficient than power pumps. Powered pumps rely on the impellers' ability to rapidly rotate the impeller to transfer mechanical energy to the fluid to increase its kinetic energy and pressure, and then through the pump cylinder to convert most of the kinetic energy to pressure energy for delivery. Power pump, also known as impeller pump or vane pump. Centrifugal pumps are the most common type of power pump. Power pump head at a certain speed has a limited value, head changes with the flow; work stable, continuous delivery, flow and pressure pulsation; generally no self-absorption capacity, the need to fill the pump first liquid or pipe pumping To work in vacuum; suitable for a wide range of performance; suitable for conveying a very small viscosity of the cleaning liquid, specially designed pump can transport mud, sewage and water transport solids. Power pumps are mainly used for water supply, drainage, irrigation, process liquid delivery, power storage, hydraulic transmission and jet propulsion. Other types of pumps are a class of pumps that deliver energy in other ways. For example, a jet pump relies on a working fluid that is jetted out at a high velocity and draws the fluid to be delivered to the pump and transfers the momentum by exchanging the two fluids for energy transfer; the water hammer pump is generated by sudden braking of flowing water Energy, so that part of the water pressure rose to a certain height; electromagnetic pump is to make the power of the liquid metal under the action of electromagnetic force, to produce flow and delivery; gas lift pump through the catheter to the compressed air or other compressed gas to the liquid The bottom, so that the formation of a lighter liquid gas-liquid mixture of fluid, and then by the pressure of the liquid outside the liquid mixture pressure up. Pump performance parameters are mainly flow and lift, in addition to shaft power, speed and necessary cavitation margin. Flow refers to the unit of time the amount of liquid output through the pump outlet, the general use of volume flow; head is the unit weight of liquid from the pump inlet to outlet of the incremental energy for the positive displacement pump, the energy increment is mainly reflected in the pressure increase , So it is usually expressed as the pressure increment instead of the head. Pump efficiency is not an independent performance parameter, it can be calculated by other performance parameters such as flow, lift and shaft power according to the formula. Conversely, known flow, lift and efficiency, but also find the shaft power. Pump performance parameters exist between a certain interdependence between changes in the pump can be tested, respectively, measured and calculated parameter values, and draw a curve to represent, these curves are called pump characteristic curve. Each pump has a specific characteristic curve provided by the pump manufacturer. The characteristic curves that are usually given at the factory also indicate the recommended performance section, which is called the working range of the pump. The actual operating point of the pump is determined by the intersection of the curve of the pump and the characteristic curve of the pump. Select and use the pump, pump operating point should fall within the scope of work, in order to ensure the operation economy and safety. In addition, the same pump delivers liquids of different viscosities, and their characteristic curves also change. In general, the characteristic curves given by the pump manufacturer mostly refer to the characteristic when conveying clean cold water. For the dynamic pump, as the liquid viscosity increases, reducing the head and efficiency, the shaft power increases, so the industry sometimes the viscosity of the liquid heating the viscosity becomes smaller, in order to improve the delivery efficiency.