Basic knowledge of the pump

First, what is the pump?

A pump is a machine that delivers or pressurizes a liquid. It transfers the mechanical energy of the prime mover or other external energy to the liquid, increasing the liquid energy.

The pump is mainly used to transport liquids such as water, oil, acid and alkali liquids, emulsions, suspoemulsions, and liquid metals, as well as liquids, gas mixtures, and liquids containing suspended solids.

Pumps can be divided into three types according to the working principle of positive displacement pumps, power pumps and other types of pumps. In addition to classification by working principle, it can be classified and named by other methods. For example, according to the driving method can be divided into electric pumps and water wheel 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; according to the nature of the liquid can be divided into Water pump, oil pump and mud pump.

There is a certain interdependence between the various performance parameters of the pump, which can be drawn as a curve, which is called the characteristic curve of the pump. Each pump has its own specific characteristic curve.

Second, the definition of the pump and historical sources

A machine that delivers or pressurizes a liquid. The pump in its broadest sense is a machine that delivers fluid or pressurizes it, including some machinery that delivers gas. The pump transfers the energy of the prime mover's mechanical energy or other energy to the liquid, increasing the energy of the liquid.

The rise 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 (previous 17th century), China's jerusalem (former 17th century), centipede (former 11th century), waterwheel (1st century AD), and 3rd century BC Ancient Greek Archimedes invented the spiral rod and so on. Around 200 BC, the ancient Greek craftsman Cte Sibius invented the most primitive piston pump-fire pump. As early as 1588, there was a record of a 4-blade vane pump. Afterwards, various other rotary pumps appeared one after another. In 1689, France's D. Papin invented a four-blade impeller volute centrifugal pump. In 1818, a centrifugal pump with a radial straight blade, a semi-open double suction impeller and a volute was introduced in the United States. From 1840 to 1850, the HR Worthington of the United States invented the piston pump that directly acted on the opposite steam of the pump cylinder and the steam cylinder, marking the formation of a 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 were introduced one after another. With the application of various advanced technologies, the efficiency of pumps has been gradually increased, and the performance range and applications have also been gradually expanded.

Third, the classification of the pump

There are many kinds of pumps. According to the working principle, they can be divided into: 1 Power type pump, also called impeller type pump or vane type pump, relying on the dynamic effect of the rotating impeller on the liquid to continuously transfer energy to the liquid, making the kinetic energy of the liquid ( Mainly) and pressure energy increase, then the kinetic energy is converted into pressure energy through the extrusion chamber, which can be further divided into centrifugal pumps, axial pumps, partial flow pumps, and vortex pumps. 2 Volumetric pumps, relying on the periodic variation of the volume of sealed working space containing liquid, periodically transfer energy to the liquid, increasing the pressure of the liquid to forcibly discharge the liquid, and can be divided into reciprocating pumps according to the motion of the working element. And rotary pump. 3 Other types of pumps that transmit energy in other forms. If the jet pump relies on the high-speed injection of the working fluid, the fluid to be pumped is sucked into the pump and mixed, and the momentum is exchanged to transfer the energy. When the water hammer pump uses the brake, part of the water in the flow is lifted to a certain height to transfer energy; the electromagnetic pump is Energized liquid metal flows under the influence of electromagnetic force to achieve delivery. In addition, the pump can be classified according to the nature of the liquid to be transported, the driving method, the structure, the use, and the like.

Fourth, the application of pumps in various fields

Judging from the performance range of the pump, the flow of the huge pump can reach hundreds of thousands of cubic meters per hour, while the flow rate of the micropump is less than tens of milliliters per hour; the pressure of the pump can be from atmospheric pressure up to 19.61Mpa (200kgf/ Cm2) Above; The temperature of the liquid to be transported is as low as -200 degrees Celsius or below and up to 800 degrees Celsius or more. The pump transports a wide variety of liquids, such as transport water (clean water, sewage, etc.), oil, acid, alkali, suspension, and liquid metal.

In the chemical and petroleum sector, raw materials, semi-finished products, and finished products are mostly liquids, and the production of semi-finished and finished products from raw materials requires a complicated process in which the pumps act as pressure fluids for transporting liquids and providing chemical reactions. In addition, pumps are used to adjust the temperature in many devices.

In agricultural production, pumps are the main irrigation and drainage machinery. China's rural areas are vast, and a large number of pumps are needed every year in rural areas. In general, agricultural pumps account for more than half of the total pump output.

Pumps are also the most used equipment in the mining and metallurgical industries. The mine needs to use a pump to drain water. In the process of beneficiation, smelting and rolling, it is necessary to use a pump to supply water first.

In the power sector, nuclear power plants require nuclear main pumps, secondary pumps, tertiary pumps, and thermal power plants that require a large number of boiler feed pumps, condensate pumps, circulating water pumps, and ash slag pumps.

In national defense construction, the use of pumps is required for the adjustment of aircraft flaps, rudder and landing gear, the rotation of warships and tank turrets, and the subsidence of submarines. High pressure and radioactive liquids, and some also require no leakage from the pump.

In the shipbuilding industry, the number of pumps used on each ocean-going wheel is generally more than one hundred, and its type is also varied. Others such as water supply and drainage in cities, water for steam locomotives, lubrication and cooling in machine tools, transport of bleaching fluids and dyes in the textile industry, transport of pulp in the paper industry, and transportation of milk and sugar in the food industry, etc. The pump.

In short, whether it is an airplane, a rocket, a tank, a submarine, or a well, a mining, a train, a ship, or a daily life, pumps are needed everywhere and there are pumps everywhere. It is this way that the pump is classified as a general-purpose machine, which is a type of raw product in the machinery industry.

Fifth, the basic parameters of the pump

The basic parameters that characterize the main performance of the pump are the following:

1, traffic Q

Flow is the amount of liquid (volume or mass) pumped out in a unit of time.

The volumetric flow is represented by Q in units of m3/s, m3/h, l/s, and so on.

Mass flow is represented by Qm in units of t/h, kg/s, and so on.

The relationship between mass flow and volume flow is:

Qm=ρQ

Where ρ - the density of the liquid (kg/m3, t/m3), normal temperature water ρ = 1000kg/m3.

2, head H

The lift is the increase in the energy of the unit weight pumped by the pump from the pump inlet (pump inlet flange) to the pump outlet (pump outlet flange). That is, the effective energy of a Newtonian liquid through the pump. The unit is N·m/N=m, which is the height of the liquid column pumped by the pump. It is customarily referred to as meter.

3, speed n

The rotation speed is the number of revolutions per unit time of the pump shaft and is denoted by the symbol n. The unit is r/min.

4, NPSH NPSH

The NPSH, also known as net positive suction, is the main parameter for cavitation performance. The NPSH was once expressed in Δh.

5, power and efficiency

Pump power usually refers to the input power, which is the power of the prime mover transmission pump shaft, it is also known as the shaft power, represented by P;

The effective power of the pump, also known as output power, is represented by Pe. It is the effective energy obtained in the pump by the liquid delivered from the pump per unit of time.

Because the head is the effective energy that the pump outputs per unit weight of liquid obtained from the pump, the product of head and mass flow and gravitational acceleration is the effective energy obtained from the liquid output from the pump in unit time—that is, the pump The effective power:

Pe=ρgQH(W)=γQH(W)

In the formula, ρ——density of the pumping liquid (kg/m3);

γ - the severity of the pump delivery fluid (N/m3);

Q - pump flow rate (m3/s);

H - Head of the pump (m);

g - Gravity acceleration (m/s2).

The difference between the shaft power P and the effective power Pe is the loss power in the pump, the size of which is measured by the efficiency of the pump. The efficiency of the pump is the ratio of effective power to shaft power, denoted by η.

What is flow? What letter? How to convert?

The volume of liquid discharged by the pump per unit time is called flow rate, and the flow rate is represented by Q. The unit of measurement is: cubic meters/hour (m3/h), liters/second (l/s), L/s=3.6 m3/h=0.06 m3/ Min=60L/min

G=Qρ G is the weight ρ is the proportion of the liquid

Example: The flow rate of a pump is 50 m3/h. How about the hourly weight for pumping? The specific gravity of water is 1000 kg/m3.

Solution: G=Qρ=50×1000(m3/h·kg/m3)=50000kg/h=50t/h

7. What is the lift? What letter? What unit of measurement? And pressure conversion and formula?

The energy gained per unit weight of liquid through the pump is called lift. The head of the pump, including the suction stroke, is approximately the pump outlet and inlet pressure difference. The head is represented by H and the unit is meter (m). The pressure of the pump is expressed by P in units of Mpa (megapascals) and H=P/ρ. If P is 1 kg/cm2, H=(lkg/cm2)/(1000kg/m3) H=(1kg/cm2)/ (1000 kg/m3)=(10000 kg/m2)/1000 kg/m3=10m

1Mpa=10kg/c m2, H=(P2-P1)/ρ (P2=outlet pressure P1=inlet pressure)

What is NPSH? What is a suction process? The respective unit of measurement represents the letter?

When the pump is working, the liquid will generate vapor under the vacuum pressure at the inlet of the impeller. Vaporized bubbles will erode the metal surface of the impeller under the impact motion of the liquid particle, thus destroying the impeller and other metals. At this time, the vacuum pressure is called Vaporization pressure and NPSH are the surplus energy of the unit weight of liquid at the pump inlet that exceeds the vaporization pressure. Units are marked with meters, using (NPSH)r. The suction process is the necessary NPSH Δh: the degree of vacuum allowed by the pump, ie the allowable installation height of the pump, in meters.

Suction stroke = standard atmospheric pressure (10.33 meters) - NPSH - safe amount (0.5 meters)

Standard atmospheric pressure pressure pipeline vacuum height of 10.33 meters.

For example: A pump must have a NPSH of 4.0 meters, and find a suction range of Δh?

Solution: Δh=10.33-4.0-0.5=5.83 meters
 

Nine, what is the cavitation phenomenon of the water pump and its cause

1, cavitation

At a certain temperature of the liquid, when the pressure is reduced to the vaporization pressure at that temperature, bubbles are generated in the liquid. This phenomenon of generating bubbles is called cavitation.

2, cavitation collapse

Bubbles generated during cavitation decrease in volume when they flow to a high pressure. This phenomenon of bubbles disappearing in the liquid due to pressure rise is called cavitation collapse.

3. Causes and hazards of cavitation

In the operation of the pump, if the partial area of ​​the overcurrent part (usually somewhere behind the inlet of the impeller blade) for some reason, the absolute pressure of the pumped liquid is reduced to the vaporization pressure of the liquid at the current temperature, the liquid will be At the beginning of the vaporization, a large amount of steam is generated and bubbles are formed. When the liquid containing a large number of bubbles passes forward through the high pressure area in the impeller, the high-pressure liquid around the bubbles causes the bubbles to drastically shrink and break. At the same time as the bubbles condense and burst, the liquid particles fill the cavities at a very high speed, creating a strong water hammer effect at this moment, and hitting the metal surface with a high impact frequency. The impact stress can reach several hundred to several thousand atmospheres. The impact frequency can reach tens of thousands of times per second, and in severe cases, the wall thickness will breakdown.

4, cavitation process

The process of generating bubbles and bursting bubbles in the pump and damaging the overflow components is the process of cavitation in the pump. After the cavitation of the water pump, in addition to damaging the flow components, noise and vibration are also generated, and the performance of the pump is reduced. In severe cases, the liquid in the pump is interrupted and cannot work normally.

X. 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. Essentially, the performance curve of the centrifugal pump is an external representation of the movement law of the liquid in the pump, and is obtained through actual measurement. Characteristic curves include: flow-head curve (QH), flow-efficiency curve (Q-η), flow-power curve (QN), flow- NPSH curve (Q-(NPSH)r), and the performance curve is Any flow point of the pump can find a set of head, power, efficiency and NPSH values ​​on the curve. This group of parameters is called the working state, referred to as the working condition or operating point, and the centrifugal pump. The conditions of the highest efficiency point are called the most processing conditions, and the most processing points are generally the design condition points. The general centrifugal pump's rated parameters are the design operating point and operating point coincide or very close. In the practice of choosing the efficiency range to run, that is to save energy, but also to ensure the normal operation of the pump, so understand the performance parameters of the pump is very important.

XI. What is the efficiency of the pump? How is the formula?

Refers to the pump's effective power and shaft power ratio. η=Pe/P

The power of the pump usually refers to the input power, that is, the power transmitted from the prime mover to the pump shaft. It is also referred to as shaft power and denoted by P.

The effective power is the product of the pump head and mass flow and gravitational acceleration.

Pe=ρg QH (W) or Pe=γQH/1000 (KW)

ρ: Density of pumping liquid (kg/m3)

γ: Severity of the pump conveying liquid γ=ρg (N/m3)

g: Gravitational acceleration (m/s)

Mass flow Qm=ρQ (t/h or kg/s)
 

Twelve, what is the pump's full performance test bench?

The equipment that can accurately test all the performance parameters of the pump through precision instruments is a full performance test bench. The national standard accuracy is Class B. The flow was measured with a precision worm gear flow meter and the head was measured with a precision pressure gauge. The suction range is measured with a precision vacuum gauge. Power is measured with a precision shaft power machine. The rotation speed was measured with a tachometer. The efficiency is calculated based on the measured value: n=rQ102.