First, what is a pump?
A pump is a machine that transports or supercharges liquids. It transfers the mechanical energy or other external energy of the prime mover to the liquid, increasing the energy of the liquid.
Pumps are mainly used to transport water, oil, acid and alkali liquid, emulsion, suspension, and liquid metals, and other liquids, but also to transport liquids, gas mixtures, and liquids containing suspended solids. Pumps can usually be divided into volume pumps, power pumps, and other types of pumps according to how they work. In addition to classification by how it works, it can be classified and named by other methods. For example, according to the driving method can be divided into electric pumps and water turbine pumps, according to the structure can be divided into single-stage pumps and multi-stage pumps, according to the use can be divided into boiler feed pumps and metering pumps, etc., according to the nature of the liquid can be divided into pumps, oil pumps, and mud pumps.
There are some interdependencies between the performance parameters of the pump, which can be represented by a curve, called the characteristic curve of the pump, each pump has its specific characteristic curve.
Second, the definition of the pump and historical sources
A machine that delivers liquids or supercharges them. Pumps in a broad sense are machinery that transports fluids or supercharges them, including some that transport gases. The pump transmits the mechanical energy of the prime mover or other energy to the liquid, increasing the energy of the liquid.
The improvement of water is very important to human life and production. There were various water-lifting instruments in ancient times, such as chain pumps in Egypt (pre-17th century), oranges in China (17th century), pickaxes (11th century), water tankers (1st century A.D.), and BC Spiral rods invented by Archimedes in ancient Greece in the 3rd century, etc. Around 200 BC, the ancient Greek artisan Ketsybius invented the most primitive piston pump – the fire pump. As early as 1588, there was a record of 4-blade slide pumps, and various other swing pumps have since emerged. In 1689, France’s D. Papin invented the snail shell centrifugal pump of the 4-blade impeller. In 1818, centrifugal pumps with radial straight blades, semi-open double-sucking impellers, and snail shells appeared in the United States. From 1840to1850, H.R. Worthington of the United States invented the piston pump, which directly acts on the steam of the pump and steam cylinder, marking the formation of the modern piston pump. From 1851to1875, multistage centrifugal pumps with guide leaves were invented one after another, making it possible to develop high-head centrifugal pumps. Subsequently, various pumps came out one after another. With the application of various advanced technologies, pump efficiency is gradually improved, the performance range and application is increasing.
Third, the classification basis of the pump
Pumps of a wide variety, according to the principle of operation can be divided into:(1) power pump, also known as impeller pump or blade pump, relying on rotating impeller on the liquid’s dynamic action, the energy continuously passed to the liquid, so that the liquid’s kinetic energy (mainly) and pressure can increase, and then through the pressure chamber to convert kinetic energy into pressure energy, but also can be divided into centrifugal pumps, axial pumps, partial flow pumps, and vortex pumps. (2) Volume pump, relying on the periodic changes of the volume of the sealed working space containing liquid, periodically transfers energy to the liquid, so that the pressure of the liquid is increased to force the liquid out, according to the movement form of the working element can be divided into the reciprocating pump and swing pump. (3) Other types of pumps transmit energy in other forms. Such as jet pump relying on high-speed injection of working fluid will need to be transported after the fluid into the pump mixing, momentum exchange to transfer energy, water hammer pump using the brake flow of some of the water is raised to a certain height to transfer energy, the electromagnetic pump is to make the electrified liquid metal under the electromagnetic force to produce flow and achieve transmission. In addition, the pump can also be classified according to the nature of the liquid transport, driving method, structure, use, etc.
Fourth, the application of pumps in various fields
In terms of pump performance, the flow rate of the giant pump can reach hundreds of thousands of cubic meters per hour, while the flow rate of the micropump is below a few tens of milliliters per hour, the pressure of the pump can be up to 19.61Mpa (200 kg/cm2) or more, and the temperature of the liquid being delivered can be as low as -200 degrees Celsius and up to 800 degrees Celsius. Pumps deliver a wide variety of liquids, such as water (clean water, sewage, etc.), fluids, acids and alkalis, suspensions, and liquid metals.
In the chemical and petroleum sectors, raw materials, semi-finished products, and finished products are mostly liquids, while the production of raw materials into semi-finished and finished products requires a complex process in which pumps act as a pressure flow to transport liquids and provide chemical reactions, in addition to the use of pumps in many devices to regulate temperature.
In agricultural production, pumps are the main drainage and irrigation machinery. China’s rural areas are vast, each year the rural areas need a large number of pumps, in general, agricultural pumps accounted for more than half of the total output of pumps.
Pumps are also the most used equipment in the mining and metallurgical industries. The mine needs to be drained by a pump, and in the process of mineral processing, smelting, and rolling, pumps are used to supply water first.
In the power sector, nuclear power plants need nuclear main pumps, secondary pumps, tertiary pumps, thermal power plants need a large number of boiler feed pumps, condensate pumps, circulating pumps, and ash pumps.
In the national defense construction, the adjustment of aircraft flaps, tail rudders and landing gear, the rotation of warships and tank turrets, the sinking of submarines, etc. all need to use pumps. High pressure and radioactive liquids, some also require the pump without any leakage, etc.
In the shipbuilding industry, the pumps used on each ocean liner are generally more than 100 units, and their types are varied. Other pumps are required, such as urban water supply and drainage, water for steam locomotives, lubrication and cooling in machine tools, drift and dye in the textile industry, pulp in the paper industry, and milk and sugar in the food industry.
In short, whether it’s aircraft, rockets, tanks, submarines, drilling, mining, trains, ships, or everyday life, pumps are needed everywhere, pumps are running everywhere. That’s why pumps are listed as general machinery, a class of raw products in the machinery industry.
V. The basic parameters of the pump
The basic parameters for the main performance of the pump are as follows:
1, Traffic Q
Flow is the amount (volume or mass) of liquid that the pump delivers in a unit of time.
Volume flow is expressedin Q inm3/s,m3/h,l/s, etc.
Mass flow is expressedin Qm int/h,kg/s, etc.
The relationship between mass flow and volume flow is:
Qm=ρQ
Medium-sized – density of liquid(kg/m3,t/m3),room temperatureclear water , ffice:smarttags” />1000kg/m3.
2, Head H
Head is the increase in energy of the unit weight liquid pumped by the pump from the pump inlet (pump inlet flange) to the pump outlet (pump outlet flange). That is, a Newtonian liquid obtains effective energy through the pump. Its unit is N.m/N=m,i.e. the height of the column that pumps the liquid, which is commonly referred to simply as meters.
3, speed n
The speed is the number of revolutions per pump shaft unit of time, expressed by the symbol n, in r/min.
4, cavitation margin NPSH
The cavitation margin, also known as the net positive tip, is the main parameter that indicates the cavitation performance. The cavitation margin has been expressed domestically in the terms of.
5, power and efficiency
The power of the pump usually refers to the input power, that is, the power on the original motive transfer pump shaft, so it is also known as the shaft power, expressed in P;
The effective power of the pump is also known as the output power, expressed in Pe. It is the effective energy obtained by the liquid sent from the pump in a unit of time.
Because head refers to the effective energy obtained from the pump by the pump output unit of heavy liquid, the product of heat and mass flow and gravity acceleration is the effective energy obtained from the liquid output from the pump in a unit of time — that is, the effective power of the pump:
Pe=ρgQH(W)=γQH(W)
medium-sized -the density of the liquid delivered by the pump(kg/m3);
γ- the symgraness of the pump’s liquid delivery(N/m3);
Q – pump flow(m3/s);
H – head of the pump (m);
g – Gravitational acceleration (m/s2).
The difference between shaft power P and effective power Pe is the loss of power in the pump, and its size is measured by the efficiency of the pump. The efficiency of the pump is the ratio of effective power to shaft power, expressed in η.
Six, what is traffic? What letters are used? How do I convert?
The volume of the pump discharge liquid per unit of time is called flow rate, which is expressed in Q and measured in cubic meters/hour (m3 /h), liters/seconds (l/s). ）, L/s=3.6 m3/h=0.06 m3/min=60L/min
G-Q-G is the weight of the liquid
Example: A pump flow rate of 50 m3/h, the weight per hour when pumping? The water weighs 1000 kg/m3.
Solution:Gs50×1000 (m3/h.kg/ m3) s50000kg / h s 50t/h
Seven, what is the head? What letters are used? In what units of measurement? and the conversion and formula of pressure?
The energy obtained by the liquid per unit weight through the pump is called the head. The head of the pump includes the suction range, approximately the difference between the pump outlet and the inlet pressure. The head is expressed in H in meters(m). The pressure of the pump is expressed in P in Mpa(mega pa),H-P/S If P is 1kg/cm2,then H is(kg/ cm2)/(1000kg/m3) H is (1kg/cm2)/(1000 kg). /m3) – (10000 kg /m2)/1000 kg /m3 x 10m
1Mpa=10kg/c m2, H=(P2-P1)/1(P2=Export Pressure P1=Import Pressure).”
Eight, what is the amount of cavitation surplus? What is sucking? Each unit of measure represents a letter?
Pumps in the work of liquid in the impeller in the inlet due to a certain vacuum pressure will produce steam, vaporized bubbles in the impact of the liquid mass movement, the impeller and other metal surfaces to produce erosion, thereby destroying the impeller and other metals, at this time vacuum pressure is called vaporization pressure, vaporization margin refers to the pumping inlet unit weight liquid has more than the vaporization pressure of surplus energy. Units are marked with meters and with(NPSH)r. The suction range is the required cavitation margin of 2x h:i.e. the vacuum degree of the pump allows the absorption of liquid, i.e. the mounting height allowed by the pump, in meters.
Suction range – Standard atmospheric pressure(10.33 m)- cavitation margin – safe amount (0.5 m).
The standard atmospheric pressure line vacuum height is 10.33 meters.
For example, a pump must have a corrosion margin of 4.0 meters, the suction range of h?
Solution:hs 10.33-4.0-0.5 s 5.83 m
Nine, what is the phenomenon of cavitation of water pumps and its causes
1, cavitation
When a liquid reduces the pressure to the vaporized pressure at a certain temperature, the liquid produces bubbles. This bubble-producing phenomenon is called vapor erosion.
2, cavitation collapse
Bubbles produced during cavitation are reduced in volume and burst when they flow to high pressure. This phenomenon, in which pressure-rising bubbles disappear into the liquid, is called cavitation and collapse.
3, the cause and harm of cavitation
When the pump is in operation, if the local area of its overflow portion (usually somewhere after the impeller blade is imported) for some reason, the absolute pressure of the pumped liquid is reduced to the liquid vaporization pressure at the prevailing temperature, where the liquid begins to vaporize, producing a large amount of steam, forming bubbles, when the liquid containing a large number of bubbles passes forward through the high-pressure area of the impeller, The high-pressure liquid around the bubble causes the bubble to shrink sharply to rupture. At the same time that the bubble condenses and breaks, the liquid mass fills the hole at a high speed, produces a very strong water shock effect in this instant, and strikes the metal surface impact stress with a high impact frequency of several hundred to thousands of atmospheres, the impact frequency can reach tens of thousands of times per second, in severe cases will break through the wall thickness.
4, cavitation process
The process of creating bubbles and cracking bubbles in the pump to damage the overcurrent components is the process of cavitation in the pump. In addition to the damaging effect on overcurrent components after the water pump has been eroded, it also produces noise and vibration, and causes the performance of the pump to decline, which in severe cases will cause the liquid in the pump to interrupt and not work properly.
Ten, what is the characteristic curve of the pump?
The curve representing the relationship between the main performance parameters is usually referred to as the performance curve or characteristic curve of the centrifugal pump, in essence, the performance curve of a centrifugal pump is an external manifestation of the motion law of liquid in the pump, which is measured by real measurement. Feature curves include: flow – head curve(Q-H), flow – efficiency curve(Q-η), flow – power curve(Q-N), flow – Cavitation margin curve(Q-(NPSH)r), the performance curve action is any flow point of the pump, you can find a set of head, power, efficiency and cavitation margin values relative to the curve, This set of parameters is called the operating state, referred to as the operating condition or operating point, the condition of the highest efficiency point of the centrifugal pump is called the best operating point, the best operating point is generally the design operating point. The rating parameters of the general centrifugal pump are that the design operating point coincides with or is very close to the optimum operating point. In practice, the selection of efficiency interval operation, that is, energy saving, but also to ensure the normal operation of the pump, so it is important to understand the performance parameters of the pump.
Eleven, what is the efficiency of the pump? What is the formula?
Refers to the ratio of the effective power of the pump to the power of the shaft. η=Pe/P
The power of the pump usually refers to the input power, that is, the power that the prime mover transmits to the pump shaft, so it is also called the shaft power, expressed in P.
Effective power is the product of the pump’s head and mass flow and gravity acceleration.
Peg QH (W) or Pe sqm/1000 (KW).
The density of the liquid delivered by the pump(kg/m3).
γ:The pump delivers a liquid with a heavy γof s.g. (N/m3).
g: Gravitational acceleration (m/s).
Mass flow Qms(t/h or kg/s).
Twelve, what is the pump’s full performance test bench?
Equipment capable of accurately testing all the performance parameters of the pump through precision instruments is a full performance test bench. The national standard accuracy is B. Flow is measured by precision worm flow meters and head by precision pressure gauges. The suction process is measured using a precision vacuum meter. Power is measured by precision shaft power machines. The speed is measured by a tachometer. The efficiency is calculated based on the measured value:n-rQ102.
