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What is a centrifugal pump

What is a centrifugal pump?

Centrifugal pump refers to a pump that transports liquid by the centrifugal force generated by the rotation of the impeller.

Centrifugal pump works by centrifugal movement of water caused by impeller rotation. Before starting the water pump, the pump shell and suction pipe must be filled with water, and then start the motor to make the pump shaft drive the impeller and water to rotate at high speed. The water is centrifugally thrown to the outer edge of the impeller and flows into the water pressure pipeline of the pump through the channel of the volute pump shell.

Structure of centrifugal pump

The basic components of centrifugal pump are high-speed rotating impeller and fixed snail shaped pump shell. Usually, the impeller of centrifugal pump with several (usually 4-12) backward curved blades is fastened on the pump shaft and rotates at high speed driven by motor with the pump shaft. Impeller is the energy supply device of centrifugal pump, which is the component that directly works on the liquid in the pump; The suction inlet in the center of the pump casing is connected with the suction pipeline, and a one-way bottom valve is installed at the bottom of the suction pipeline; The discharge port on the side of the pump casing is connected with the discharge pipeline equipped with a regulating valve.
The basic structure of centrifugal pump is composed of six parts: impeller, pump body, pump shaft, bearing, sealing ring and stuffing box.There are many kinds of centrifugal pumps. Although the structures of various types of pumps are different, the main parts are basically the same.
The main components of centrifugal pump include: impeller, pump shaft, pump housing, pump seat, packing box (shaft seal device), leakage reduction ring, bearing seat, etc.
1. Impeller
Impeller is an important part of centrifugal pump. It depends on its high-speed rotation to do work on liquid to realize liquid transportation. It is an important part of centrifugal pump.
The impeller is generally composed of wheel hub, blade and cover plate. The cover plate of the impeller is divided into front cover plate and rear cover plate. The cover plate on the side of the impeller port is called the front cover plate, and the cover plate on the other side is called the rear cover plate.
When the centrifugal pump is started, the pump shaft drives the impeller to rotate at high speed, forcing the liquid pre filled between the blades to rotate. Under the action of inertial centrifugal force, the liquid moves radially from the center of the impeller to the periphery.
When the liquid flows through the impeller, it obtains energy, the static pressure energy increases and the flow rate increases. When the liquid leaves the impeller and enters the pump housing, it slows down due to the gradual expansion of the flow channel in the housing, part of the kinetic energy is converted into static pressure energy, and finally flows into the discharge pipeline along the tangential direction.
According to the structural form, the impeller can be divided into the following three types.

  • (1) there are cover plates on both sides of the closed impeller, and there are 4-6 blades between the cover plates. The closed impeller has high efficiency and is the most widely used. It is suitable for conveying clean liquid without solid particles and fibers.
  • (2) the open impeller has no cover plate on both sides of the blade, which is suitable for conveying the liquid containing a large amount of suspended solids, with low efficiency and low liquid pressure.
  • (3) semi open impeller this kind of impeller has only rear cover plate. It is suitable for conveying liquids that are easy to precipitate or contain solid suspended solids. Its efficiency is between open and closed impellers.

2. Pump shaft
The main function of the pump shaft of centrifugal pump is to transmit power and support the impeller to keep it in normal operation in the working position. One end is connected with the motor shaft through a coupling, the other end supports the impeller for rotary movement, and the shaft is equipped with bearings, axial seals and other parts.
The common materials of pump shaft are carbon steel and stainless steel.
The impeller and shaft are connected by keys. Because this connection method can only transmit torque and can not fix the axial position of the impeller, the axial position of the impeller should be fixed by shaft sleeve and lock nut in the water pump.
After the impeller is axially positioned with the lock nut and the shaft sleeve, in order to prevent the lock nut from retracting, the reverse rotation of the water pump shall be prevented, especially for the initially installed water pump or the water pump after disassembly and maintenance, the steering inspection shall be carried out according to the regulations to ensure that the steering is consistent with the regulations.
3. Shaft sleeve

20210816102407 70800 - What is a centrifugal pump

The function of the shaft sleeve is to protect the pump shaft and change the friction between the packing and the pump shaft into the friction between the packing and the shaft sleeve, so the shaft sleeve is an easily worn part of the centrifugal pump.

Generally, the surface of shaft sleeve can also be treated by carburizing, nitriding, chromium plating and spraying. The surface roughness shall generally meet the requirements of Ra3.2 μm—Ra0.8 μm. It can reduce the friction coefficient and improve the service life.
4. Bearing
The bearing supports the weight and bearing force of the rotor. Rolling bearings are mostly used on centrifugal pumps. The outer ring and bearing seat hole are made of base shaft, and the inner ring and rotating shaft are made of base hole. The matching category has recommended values in national standards, which can be selected according to specific conditions. Bearings are generally lubricated with grease and oil.
5. Stuffing box
When the pump shaft passes through the pump housing, there is a gap between the shaft and the housing. In the single suction centrifugal pump, if the shaft seal device is not used in this part, the high-pressure water in the pump shell will leak out. Stuffing box is a common shaft sealing device. The packing box is composed of shaft seal sleeve, packing, water seal pipe, water seal ring and packing gland.
6. Volute
Volute refers to the spiral flow channel with gradually increasing cross-sectional area from the impeller outlet to the inlet of the next stage impeller or to the outlet pipe of the pump. The flow channel is gradually expanded, and the outlet is a diffusion tube. After the liquid flows out of the impeller, its velocity can be gently reduced, so that a large part of the kinetic energy is transformed into static pressure energy.
The advantages of volute are convenient manufacture, wide efficiency area and small change in pump efficiency after turning impeller.
The disadvantage is that the volute shape is asymmetric. When using a single volute, the pressure acting on the radial direction of the rotor is uneven, which is easy to bend the shaft. Therefore, in the multi-stage pump, only the volute is used in the first section and tail section, and the guide wheel device is used in the middle section.
The spiral case is generally made of cast iron. The volute of the anti-corrosion pump is made of stainless steel or other anti-corrosion materials, such as plastic, FRP, etc. The volute of multistage pump is generally made of cast steel because of its high pressure and high requirements for material strength.
7. Guide wheel
The guide wheel is a fixed disc, with forward guide vanes wrapped around the outer edge of the impeller on the front, which form a diffusion channel, and reverse guide vanes to guide the liquid to the next stage impeller on the back. After the liquid is thrown out of the impeller, it gently enters the guide wheel and continues to flow outward along the forward guide vane, the speed gradually decreases, and most of the kinetic energy is transformed into static pressure energy.
The radial unilateral clearance between impeller and guide vane is about 1mm. If the gap is too large, the efficiency will be reduced; If the clearance is too small, it will cause vibration and noise. Compared with the volute, the segmented multistage centrifugal pump with guide wheel is easy to manufacture and has higher energy conversion efficiency. However, installation and maintenance are more difficult than volute.
8. Sealing ring
In order to reduce internal leakage and protect the pump housing, a removable sealing ring is installed on the housing corresponding to the inlet of the impeller. The radial clearance between the inner hole of the sealing ring and the outer circle of the impeller is generally between 0.1-0.2mm. After the seal ring is worn, the radial clearance increases, the discharge volume of the pump decreases and the efficiency decreases. When the seal clearance exceeds the specified value, it shall be replaced in time.
There are three structural forms of sealing ring:

  • Flat ring type, simple structure, convenient manufacture, but poor sealing effect;
  • The right angle sealing ring passes through a 90 ° channel when the liquid leaks. The sealing effect is better than the flat ring type and is widely used;
  • Labyrinth seal ring has good sealing effect, but its structure is complex and difficult to manufacture. It is rarely used in general centrifugal pump.

Types of centrifugal pumps

In the process of fluid flow, some mechanical energy will be lost due to flow resistance. Therefore, according to the flow required for production, it is necessary to provide mechanical energy to the fluid from one place to another, whether it is from the lower part of the total specific energy to the higher part of the total specific energy, or only overcome the flow resistance. The machinery used to transport liquid is called pump.

Classification by impeller number

1. Single stage pump: that is, there is only one impeller on the pump shaft.
2. Multistage pump: that is, there are two or more impellers on the pump shaft. At this time, the total head of the pump is the sum of the heads generated by N impellers.

Classified by working pressure

1. Low pressure pump: the pressure is lower than 100m water column;
2. Medium pressure pump: the pressure is between 100 ~ 650 m water column;
3. High pressure pump: the pressure is higher than 650 m water column.

Classified by impeller suction mode

1. Single side water inlet pump: also known as single suction pump, that is, there is only one water inlet on the impeller;
2. Double side water inlet pump: also known as double suction pump, that is, there is a water inlet on both sides of the impeller. Its flow is twice as large as that of the single suction pump, which can be roughly regarded as two single suction pump impellers placed back-to-back together.

Classified by pump casing combination

1. Horizontal split pump: a joint is opened on the horizontal plane passing through the axis line.
2. Vertical joint surface pump: that is, the joint surface is perpendicular to the axis.

Classified by pump shaft position

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1. Horizontal pump: the pump shaft is in the horizontal position.
2. Vertical pump: the pump shaft is in the vertical position.

Classification by impeller outlet mode

1. Volute pump: after water comes out of the impeller, it directly enters the pump shell with spiral shape.
2. Guide vane pump: after water comes out of the impeller, it enters the guide vane set outside it, and then enters the next stage or flows into the outlet pipe.

Classification by installation height

1. Self filling centrifugal pump: the pump shaft is lower than the surface of the suction tank. It can be started automatically without filling water.
2. Suction centrifugal pump (non self filling centrifugal pump): the pump shaft is higher than the surface of the suction tank. Before start-up, it is necessary to fill the pump casing and suction pipe with water, and then drive the motor to make the impeller rotate at high speed. The water is thrown out of the impeller under the action of centrifugal force, and a negative pressure is formed in the center of the impeller. The water in the suction tank enters the impeller under the action of atmospheric pressure, and is thrown out of the impeller into the pressurized water pipe under the action of high-speed rotating impeller.
In addition, it can also be classified according to the purpose, such as oil pump, water pump, condensate pump, ash discharge pump, circulating water pump, etc.

Working principle of centrifugal pump

working principle of centrifugal pump - What is a centrifugal pump

After the centrifugal pump is started, the pump shaft will drive the impeller to rotate at high speed, forcing the liquid pre filled between the blades to rotate. Under the action of inertial centrifugal force, the liquid will move radially from the center of the impeller to the periphery. The liquid medium will obtain energy during the movement through the impeller, resulting in the increase of static pressure energy and flow velocity. When the liquid leaves the impeller and enters the pump housing, it slows down due to the gradual expansion of the flow channel in the housing, part of the kinetic energy is converted into static pressure energy, and finally flows into the discharge pipeline along the tangential direction. When the liquid is thrown from the center of the impeller to the outside, a low-pressure area will be formed in the center of the impeller. Under the action of the total potential energy difference between the liquid level of the storage tank and the center of the impeller, the liquid will be sucked into the center of the impeller. Depending on the continuous operation of the impeller, the liquid will be continuously inhaled and discharged. The mechanical energy obtained by liquid in centrifugal pump finally shows the improvement of static pressure energy.
Centrifugal pump can send water out because of the action of centrifugal force. Before the pump works, the pump body and water inlet pipe must be filled with water to form a vacuum state. When the impeller rotates rapidly, the blade promotes the water to rotate quickly. The rotating water flies away from the impeller under the action of centrifugal force. After the water in the pump is thrown out, the central part of the impeller forms a vacuum area. Under the action of atmospheric pressure (or water pressure), the water of Shuiyuan is pressed into the inlet pipe through the pipe network. In this way, continuous pumping can be realized. It is worth mentioning here that before starting the centrifugal pump, the pump shell must be filled with water before starting, otherwise the pump body will not be able to complete liquid absorption, causing the pump body to heat, vibrate, no water, produce “idling”, damage the pump (hereinafter referred to as “air binding”) and cause equipment accidents.

Use of pumps

The test run of the pump shall meet the following requirements:

  • ① The steering of the driving machine shall be the same as that of the pump;
  • ② Find out the steering direction of pipeline pump and coaxial pump;
  • ③ Each fixed connection part shall be free of looseness, and the specification and quantity of lubricant added to each lubricating part shall comply with the provisions of equipment technical documents;
  • ④ The parts with pre lubrication requirements shall be pre lubricated as required;
  • ⑤ All indicating instruments and safety protection devices shall be sensitive, accurate and reliable;
  • ⑥ The turning gear shall be flexible without abnormalities;
  • ⑦ The pump body shall be preheated before the test run of the high-temperature pump, the temperature shall rise evenly, and the temperature rise per hour shall not be greater than 50 ℃; The temperature difference between the pump surface and the process pipeline with working medium inlet shall not be greater than 40 ℃;
  • ⑧ A connecting device is set to eliminate the influence of temperature rise, and a bypass connecting device is set to provide cooling water source.

The following points shall be noted during the operation of centrifugal pump:

  • ① Do not operate without water, do not adjust the suction port to reduce the displacement, and do not operate under too low flow;
  • ② Monitor the operation process, completely prevent the leakage of the stuffing box, and use new packing when replacing the stuffing box;
  • ③ Ensure that the mechanical seal has sufficient flushing water flow, and excessive water flow is prohibited for water-cooled bearings;
  • ④ Do not use too much lubricant;
  • ⑤ Check according to the recommended cycle. Establish operation records, including operation hours, adjustment and replacement of packing, lubricant addition and other maintenance measures and time. The suction and discharge pressure, flow, input power, temperature and vibration of washing solution and bearing of centrifugal pump shall be measured and recorded regularly.
  • ⑥ The main engine of the centrifugal pump depends on atmospheric pressure to pump the water at the low place to the high place, and the atmospheric pressure can only support about 10.3M water column at most, so the main engine of the centrifugal pump cannot work 12 meters away from the water surface.

Maintenance of centrifugal pump

Failure analysis of mechanical seal of centrifugal pump

The shutdown of centrifugal pump is mainly caused by the failure of mechanical seal. Most of the failure manifestations are leakage, and the leakage causes are as follows:

  • ① The main reasons for the leakage of the sealing surface of the dynamic and static ring are: the flatness and roughness of the end face do not meet the requirements, or the surface is scratched; There is particulate matter between the end faces, resulting in the same operation of both ends; The installation is not in place and the method is incorrect.
  • ② The main reasons for the leakage of the compensation ring seal ring are: the gland is deformed and the preload is uneven; Incorrect installation; The quality of sealing ring does not meet the standard; Incorrect seal ring selection.

The actual application results show that the most failed parts of the sealing elements are the end face of the dynamic and static ring, and the cracking of the end face of the static ring of the centrifugal pump is a common failure phenomenon. The main reasons are as follows:

  • ① During installation, the clearance between sealing surfaces is too large, and the flushing fluid has no time to take away the heat generated by the friction pair; The flushing fluid leaked from the gap of the sealing surface, resulting in overheating and damage of the end face.
  • ② The vaporization and expansion of liquid medium makes the two ends separated by the vaporization and expansion force. When the two sealing surfaces are firmly bonded, the lubricating film is damaged, resulting in overheating of the end surface.
  • ③ The lubricity of liquid medium is poor, and the operating pressure is overloaded, so the tracking rotation of the two sealing surfaces is not synchronous. For example, the rotating speed of the high-speed pump is 20445r/min, and the central diameter of the sealing surface is 7cm. After the pump is running, its linear speed is as high as 75m/s. when a sealing surface lags behind and cannot track the rotation, the instantaneous high temperature will cause damage to the sealing surface.
  • ④ The sealing flushing liquid orifice or filter screen is blocked, resulting in insufficient water and failure of the mechanical seal.

In addition, the sliding groove on the surface of the sealing surface and the gap in the fitting of the end face lead to the failure of the sealing element. The main reasons are:

  • ① The liquid medium is not clean and has small hard particles, which slide onto the sealing surface at a high speed and scratch the end surface and become invalid.
  • ② The coaxiality of the pump transmission parts is poor. After the pump is started, the end face is shaken and rubbed once every revolution, and the moving ring running track is not concentric, resulting in end face vaporization, overheating and wear.
  • ③ The frequent occurrence of hydraulic characteristics of liquid medium causes the vibration of pump unit, resulting in the dislocation of sealing surface and failure.

The corrosion of liquid medium to sealing elements, stress concentration, coordination of soft and hard materials, erosion, incompatibility between auxiliary seal 0-ring, V-ring, concave ring and liquid medium, deformation, etc. will cause damage and failure of mechanical seal surface. Therefore, the damage form should be comprehensively analyzed to find out the root cause and ensure the long-term operation of mechanical seal.

Requirements after centrifugal pump stops running

  • ① After the centrifugal pump stops running, close the population valve of the pump, and then close the valves of the auxiliary system after the pump cools down.
  • ② The shutdown of high-temperature pump shall be carried out according to the provisions of equipment technical documents. After shutdown, turn for half a turn every 20-30min until the pump body temperature drops to 50 ℃.
  • ③ When the cryogenic pump is stopped, when there are no special requirements, the pump shall be often filled with liquid; The suction valve and discharge valve shall be kept normally open; For cryogenic pumps with double face mechanical seals, the level controller and the sealing fluid in the pump sealing cavity shall maintain the grouting pressure of the pump.
  • ④ For the pump conveying media easy to crystallize, solidify and precipitate, the pump shall be prevented from blocking after stopping the pump, and the pump and pipeline shall be washed with clean water or other media in time. ⑤ Discharge the liquid accumulated in the pump to prevent corrosion and frost crack.

Storage of centrifugal pump

  • ① The pump that has not been installed shall be coated with a layer of appropriate antirust agent on the unpainted surface, the oil lubricated bearing shall be filled with appropriate oil, and the grease lubricated bearing shall be filled with only one kind of grease instead of mixed grease.
  • ② Pump clean liquid for a short time, flush, suction pipeline, discharge pipeline, pump casing and impeller, and drain the flushing liquid in pump casing, suction pipeline and discharge pipeline.
  • ③ Drain the oil from the bearing box, fill it with clean oil, thoroughly clean the grease and fill it with new grease.
  • ④ Seal the suction port and discharge port, store the pump in a clean and dry place, protect the motor winding from moisture, and spray the inside of the pump shell with antirust fluid and anti-corrosion fluid.
  • ⑤ Rotate the pump shaft once a month to avoid freezing, and lubricate the bearing.

Startup of centrifugal pump

Preparation before starting centrifugal pump

a. Inspection before starting centrifugal pump

  • Whether the name, model, main performance and filling quantity of lubricating oil meet the requirements of technical documents;
  • Whether the bearing lubrication system, sealing system and cooling system are intact, and whether the oil and water circuits of the bearing are unblocked;
  • Turn the rotor of the pump for 1 ~ 2 revolutions to check whether the rotor is rubbed or stuck;
  • Whether there are sundries hindering rotation near the coupling or belt protection device;
  • Whether the foundation anchor bolts of pump, bearing seat and motor are loose;
  • The valve or accessory device of the pump working system shall be at the position with the minimum load during pump operation, and the outlet regulating valve shall be closed;
  • Point pump, to see whether the impeller steering is consistent with the design of steering. If it is not consistent, the impeller must be completely stopped after the adjustment of the motor connection, before it can start again.

b. Water filling of centrifugal pump
Before starting the pump, the pump shell and suction pipe must be filled with water, because the vacuum at the pump suction inlet cannot be formed and maintained in the presence of air.
c. Centrifugal pump warm-up
Multistage centrifugal pumps conveying high-temperature liquid, such as boiler feed pump of power plant, must warm up the pump before startup. This is because when the feed pump is started, the high-temperature feed water flows through the pump, which will quickly increase the temperature of the pump body from normal temperature to 100 ~ 200 ℃, which will cause the temperature difference between the inside and outside of the pump and between various components. If there is no long enough heat transfer time and appropriate temperature rise control measures, the expansion of the pump will be uneven, resulting in deformation, wear, vibration and bearing shaft holding accidents of all parts of the pump body.

Precautions

Centrifugal pump is a vane pump, which relies on the rotating impeller. In the process of rotation, due to the interaction between the blade and the liquid, the blade transmits mechanical energy to the liquid, so that the pressure of the liquid can be increased to achieve the purpose of conveying the liquid. Four points shall be paid attention to when starting the centrifugal pump:

  • ① The head produced by centrifugal pump at a certain speed has a limited value. The operating point flow and shaft power depend on the condition of the device system connected to the pump (level difference, pressure difference and pipeline loss). The head varies with the flow.
  • ② Stable operation, continuous transportation, no pulsation of flow and pressure.
  • ③ Generally, it has no self-priming capacity. It is necessary to fill the pump with liquid or vacuum the pipeline before starting to work.
  • ④ The centrifugal pump is started when the discharge pipeline valve is closed, and the vortex pump and axial flow pump are started when the valve is fully open to reduce the starting power.

Because the centrifugal pump relies on the suction of the vacuum formed by the centrifugal force of the impeller to lift the water, when the centrifugal pump is started, the gate valve must be closed and filled with water. When the water level is above the impeller, discharge the air in the centrifugal pump before starting. After startup, a vacuum is formed around the impeller to suck up the water, and the gate valve can be opened automatically to lift the water. Therefore, the gate valve must be closed first.

Vibration analysis 

  • 1. The rotor of centrifugal pump is unbalanced and misaligned. This problem accounts for a large proportion in the vibration problem of centrifugal pump, which is about 80%. Factors causing the imbalance of centrifugal pump rotor: uneven materials and unqualified part structure, resulting in the non coincidence of rotor mass center line and rotating shaft center line, resulting in the imbalance caused by eccentricity. There are two ways to correct the rotor imbalance of centrifugal pump. Static balance and dynamic balance: also known as single-sided balance and double-sided balance. The difference is that single-sided balance is corrected and balanced on one calibration front, while double-sided balance is corrected and balanced on two calibration front.
  • 2. Installation reason: the foundation bolt is loose and the levelness of calibration is not adjusted well. Before the centrifugal pump works, check whether the foundation bolt is loose and whether the installation of the centrifugal pump is horizontal. These will also cause vibration when the centrifugal pump is working.
  • 3. There are foreign matters in the centrifugal pump. Before the centrifugal pump works, check the inside of the pump. Due to long-term use, there may be some foreign matters such as weeds in the water in the inside of the centrifugal pump.
  • 4. Cavitation perforation inside the centrifugal pump caused by long-term use.
  • 5. There are unreasonable conditions in the design of centrifugal pump, such as the size of parts, etc. However, this situation is relatively rare. Before leaving the factory, the centrifugal pump will be tested many times in the workshop to ensure the qualified rate of the centrifugal pump.

Main performance of centrifugal pump

Power and efficiency of centrifugal pump

Due to various losses during the operation of the pump, the actual (effective) head and flow of the pump are lower than the theoretical value, and the power of the input pump is higher than the theoretical value

  • H – the effective head of the pump, i.e. the energy obtained from the pump by a unit amount of liquid in the gravity field, m;
  • Q – actual flow of pump, m3/S;
  • ρ- Liquid density, kg/m3;
  • NE – the effective power of the pump, i.e. the mechanical energy obtained by the liquid from the pump per unit time, W.

The effective power can be written as Ne = QHρg
The power input to the centrifugal pump by the motor is called the shaft power of the pump, expressed in n. The ratio of effective power to shaft power is defined as the total efficiency of the pump η, Namely η= Ne/N.

Loss in pump

Various losses in centrifugal pump include:
(1) Volume loss
The loss caused by the leakage of the pump is called volume loss. The ratio of pump power without volume loss to pump power with volume loss is called pump volumetric efficiency η v。
(2) Hydraulic loss
When the fluid flows through the impeller and pump shell, the change of velocity and direction and the existence of inverse pressure gradient cause circulation and vortex, resulting in energy loss, which is called hydraulic loss. Hydraulic efficiency of centrifugal pump at rated flow η H is generally 0.8 to 0.9.
(3) Mechanical loss
The loss caused by the friction between the high-speed rotating impeller and the liquid and the mechanical friction at the bearing and shaft seal is called mechanical loss. Mechanical efficiency η M is generally 0.96 to 0.99.
Be careful:

  • 1. The main performance parameters indicated on the nameplate of centrifugal pump are the values measured under the condition of maximum efficiency with 20 ℃ clean water.
  • 2. Understand and master the meaning and use conditions of each curve in the characteristic curve, and pay attention to the range of the highest efficiency area(η=92%ηmax) and purpose.
Centrifugal pump parameters
Flow Q
Lift
m
Efficiency
%
Speed
r/min
Motor power
KW
Allowable NPSH
m
m3/h
l/s
15-80
1.5
0.42
8
34
2800
0.18
2.3
20-110
2.5
0.69
15
34
2800
0.37
2.3
20-160
2.5
0.69
32
25
2900
0.75
2.3
25-110
4
1.11
15
42
2900
0.55
2.3
25-125
4
1.11
20
36
2900
0.75
2.3
25-125A
3.6
1.0
16
35
2900
0.55
2.3
25-160
4
1.11
32
32
2900
1.5
2.3
25-160A
3.7
1.03
28
31
2900
1.1
2.3
32-100
4.5
12.5
12.5
44
2900
0.55
2.3
32-100(I)
6.3
1.75
12.5
54
2900
0.75
2.3
32-125
5
1.39
20
44
2900
0.75
2.3
32-125A
4.5
1.25
16
43
2900
0.55
2.3
32-160
6.5
5
32
44
2900
1.5
2.3
32-160A
4
1.1
25
34
2900
1.1
2.0
32-160(I)
6.3
1.75
32
40
2900
2.2
2.0
32-200
4.5
12.5
50
32
2900
3
2.0
32-200(I)
6.3
1.75
50
33
2900
4
2.0
32-200A
4
1.11
44
40
2900
2.2
2.0
40-100
6.3
1.75
12.5
54
2900
0.55
2.3
40100A
5.6
1.56
10
52
2900
0.37
2.3
40-125
6.3
1.75
20
46
2900
1.1
2.3
40-125A
5.6
1.56
16
45
2900
0.75
2.3
40-160
6.3
1.75
32
40
2900
2.2
2.3
40-160A
5.9
1.64
28
39
2900
1.5
2.3
40-160B
5.5
1.53
24
38
2900
1.1
2.3
40-200
6.3
1.75
50
33
2900
4
2.3
40-200A
5.9
1.64
44
31
2900
3
2.3
40-200B
5.3
1.47
36
29
2900
2.2
2.3
40-250
6.3
1.75
80
28
2900
7.5
2.3
40-250A
5.9
1.64
70
28
2900
5.5
2.3
40-250B
5.5
1.53
60
27
2900
4
2.3
40-100(I)
12.5
3.47
12.5
62
2900
1.1
2.3
40-100(I)A
11
3.05
10
60
2900
0.75
2.3
40-125(I)
12.5
3.47
20
58
2900
1.5
2.3
40-125(I)A
11
3.05
16
57
2900
1.1
2.3
40-160(I)
12.5
3.47
32
52
2900
3
2.3
40-160(I)A
11.7
3.25
28
51
2900
2.2
2.3
40-160(I)B
10.4
2.89
22
50
2900
1.5
2.3
40-200(I)
12.5
3.47
50
46
2900
5.5
2.3
40-200(I)A
11.7
3.25
44
45
2900
4
2.3
40-200(I)B
10.6
2.94
36
44
2900
3
2.3
40-250(I)
12.5
3.47
80
38
2900
11
2.3
40-250(I)A
11.6
3.22
70
38
2900
7.5
2.3
40-250(I)B
10.8
3.0
60
37
2900
7.5
2.3
40-250(I)C
10.0
2.78
52
36
2900
5.5
2.3
50-100
12.5
3.47
12.5
62
2900
1.1
2.3
50-100A
11
3.05
10
60
2900
0.75
2.3
50-125
12.5
3.47
20
58
2900
1.5
2.3
Model
Flow Q
Lift
m
Efficiency
%
Speed
r/min
Motor power
KW
Allowable NPSH
m
m/h
l/s
50-125A
11
3.05
16
57
2900
1.1
2.3
50-160
12.5
3.47
32
52
2900
3
2.3
50-160A
11.7
3.25
28
51
2900
2.2
2.3
50-160B
10.4
2.89
22
50
2900
1.5
2.3
50-200
12.5
3.47
50
46
2900
5.5
2.3
50-200A
11.7
3.25
44
45
2900
4
2.3
50-200B
10.6
2.94
36
44
2900
3
2.3
50-250
12.5
3.47
80
38
2900
11
2.3
50-250A
11.6
3.22
70
38
2900
7.5
2.3
50-250B
10.8
3.0
60
37
2900
7.5
2.3
50-250C
10.0
2.78
52
36
2900
5.5
2.3
50-100(I)
25
6.94
12.5
69
2900
1.5
2.5
50-100(I)A
22.3
6.19
10
67
2900
1.1
2.5
50-125(I)
25
6.94
20
68
2900
3
2.5
50-125(I)A
22.3
6.19
16
66
2900
2.2
2.5
50-160(I)
25
6.94
32
63
2900
4
2.5
50-160(I)A
23.4
6.5
28
62
2900
4
2.5
50-160(I)B
21.6
6.0
24
58
2900
3
2.5
50-200(I)
25
6.94
50
58
2900
7.5
2.5
50-200(I)A
23.5
6.53
44
57
2900
7.5
2.5
50-200(I)B
21.8
6.06
38
55
2900
5.5
2.5
50-250(I)
25
6.94
80
50
2900
15
2.5
50-250(I)A
23.4
6.5
70
50
2900
11
2.5
50-250(I)B
21.6
6.0
60
49
2900
11
2.5
50-315(I)
25
6.94
125
40
2900
30
2.5
50-315(I)A
23.7
6.58
113
40
2900
22
2.5
50-315(I)B
22.5
6.25
101
39
2900
18.5
2.5
50-315(I)C
20.6
5.72
85
38
2900
15
2.5
65-100
25
6.94
12.5
69
2900
1.5
2.5
65-100A
22.3
6.19
10
67
2900
1.1
2.5
65-125
25
6.94
20
68
2900
3
2.5
65-125A
22.3
6.19
16
66
2900
2.2
2.5
65-160
25
6.94
32
63
2900
4
2.5
65-160A
23.4
6.5
28
62
2900
4
2.5
65-160B
21.6
6.0
24
58
2900
3
2.5
65-200
25
6.94
50
58
2900
7.5
2.5
65-200A
23.5
6.53
44
57
2900
7.5
2.5
65-200B
21.8
6.06
38
55
2900
5.5
2.5
65-250
25
6.94
80
50
2900
15
2.5
65-250A
23.4
6.5
70
50
2900
11
2.5
65-250B
21.6
6.0
60
49
2900
11
2.5
65-315
25
6.94
125
40
2900
30
2.5
65-315A
23.7
6.58
113
40
2900
22
2.5
65-315B
22.5
6.25
101
39
2900
18.5
2.5
65-315C
20.6
5.72
85
38
2900
15
2.5
65-100(I)
50
13.9
12.5
73
2900
3
3.0
65-100(I)A
44.7
12.4
10
72
2900
2.2
3.0
65-125(I)
50
13.9
20
72.5
2900
5.5
3.0
Model
Flow Q
Lift
m
Efficiency
%
Speed
r/min
Motor power
KW
Allowable NPSH
m
m/h
l/s
65-125(I)A
45
12.5
16
71
2900
4
3.0
65-160(I)
50
13.9
32
71
2900
7.5
3.0
65-160(I)A
46.7
13.0
28
70
2900
7.5
3.0
65-160(I)B
43.3
12.0
24
69
2900
5.5
3.0
65-200(I)
50
13.9
50
67
2900
15
3.0
65-200(I)A
47
13.1
44
66
2900
11
3.0
65-200(I)B
43.5
12.1
38
65
2900
7.5
3.0
65-250(I)
50
13.9
80
59
2900
22
3.0
65-250(I)A
46.7
13.0
70
59
2900
18.5
3.0
65-250(I)B
43.3
12.0
60
58
2900
15
3.0
65-315(I)
50
13.9
125
54
2900
37
3.0
65-315(I)A
46.5
12.9
110
54
2900
30
3.0
65-315(I)B
44.5
12.4
100
53
2900
30
3.0
65-315(I)C
41
11.4
85
51
2900
22
3.0
80-100
50
13.9
12.5
73
2900
3
3.0
80-100A
44.7
12.5
10
72
2900
2.2
3.0
80-125
50
13.9
20
72.5
2900
5.5
3.0
80-125A
45
12.5
16
71
2900
4
3.0
80-160
50
13.9
32
71
2900
7.5
3.0
80-160A
46.7
13.0
28
70
2900
7.5
3.0
80-160B
43.3
12.0
24
69
2900
5.5
3.0
80-200
50
13.9
50
67
2900
15
3.0
80-200A
47
13.1
44
66
2900
11
3.0
80-200B
43.5
12.1
38
65
2900
7.5
3.0
80-250
50
13.9
80
59
2900
22
3.0
80-250A
46.7
13.0
70
59
2900
18.5
3.0
80-250B
43.3
12.0
60
58
2900
15
3.0
80-315
50
13.9
125
54
2900
37
3.0
80-315A
46.5
12.9
110
54
2900
30
3.0
80-315B
44.5
12.4
100
53
2900
30
3.0
80-315C
41
11.4
85
51
2900
22
3.0
80-350
50
13.9
150
66
2900
55
3.0
80-350A
44.5
12.4
142
65
2900
45
3.0
80-350B
41
11.4
135
62
2900
37
3.0
80-100(I)
100
27.8
12.5
76
2900
5.5
4.5
80-100(I)A
89
24.7
10
74
2900
4
4.5
80-125(I)
100
27.8
20
76
2900
11
4.5
80-125(I)A
89
24.7
16
74
2900
7.5
4.5
80-160(I)
100
27.8
32
76
2900
15
4.5
80-160(I)A
93.5
26.0
28
74
2900
11
4.5
80-160(I)B
86.6
24.1
24
72
2900
11
4.5
80-200(I)
100
27.8
50
74
2900
2
4.5
80-200(I)A
93.5
26.0
44
73
2900
18.5
4.5
80-200(I)B
87
24.2
38
71
2900
15
4.5
80-250(I)
100
27.8
80
69
2900
37
4.5
80-250(I)A
93.5
26.0
70
68
2900
30
4.5
80-250(I)B
87
24.2
60
66
2900
30
4.5
80-315(I)
100
27.8
125
66
2900
75
4.5
Model
Flow Q
Lift
m
Efficiency
%
Speed
r/min
Motor power
KW
Allowable NPSH
m
m/h
l/s
80-315(I)A
95
26.4
113
66
2900
55
4.0
80-315(I)B
90
25
101
65
2900
45
4.0
80-315(I)C
82
22.8
85
63
2900
37
4.0
100-100
100
27.8
12.5
76
2900
5.5
4.5
100-100A
89
47
10
74
2900
4
4.5
100-125
100
27.8
20
76
2900
11
4.5
100-125A
89
24.7
16
74
2900
7.5
4.5
100-160
100
27.8
32
76
2900
15
4.5
100-160A
93.5
26.0
28
74
2900
11
4.5
100-160B
86.6
24.1
24
72
2900
11
4.5
100-200
100
27.8
50
74
2900
22
4.0
100-200A
93.5
26.0
44
73
2900
18.5
4.0
100-200B
87
24.2
38
71
2900
15
4.0
100-250
100
27.8
80
69
2900
37
4.0
100-250A
93.5
26.0
70
68
2900
30
4.0
100-250B
87
24.2
60
66
2900
30
4.0
100-315
100
27.8
125
66
2900
75
4.0
100-315A
95
26.4
113
66
2900
55
4.0
100-315B
90
25
101
65
2900
45
4.0
100-315C
82
22.8
85
63
2900
37
4.0
100-100(I)
160
44.4
12.5
73
2900
11
4.5
100-125(I)
160
44.4
20
74
2900
15
4.5
100-125(I)A
140
39
17
72
2900
11
4.5
100-160(I)
160
44.4
32
32
2900
22
5.6
100-160(I)A
140
39
28
28
2900
18.5
5.0
100-200(I)
100
44.4
50
50
2900
37
5.2
100-200(I)A
140
39
45
45
2900
30
4.5
100-200(I)B
100
27.8
40
40
2900
22
4.5
100-250(I)
160
44.4
80
80
2900
55
4.8
100-250(I)A
140
39
72
72
2900
45
4.5
100-250(I)B
100
27.8
65
65
2900
37
4.5
100-350
100
27.8
150
150
2900
90
4.0
100-350A
87
24.2
142
142
2900
75
4.0
100-350B
82
22.8
135
135
2900
55
4.0
125-100
160
44.4
12.5
12.5
2900
11
4.0
125-100A
143
39.7
10
10
2900
7.5
4.0
125-125
160
44.4
20
20
2900
15
4.0
125-125A
143
39.7
16
16
2900
11
4.0
125-160
160
44.4
32
32
2900
22
4.0
125-160A
150
41.7
28
28
2900
18.5
4.0
125-160B
138
38.3
24
24
2900
15
4.0
125-200
160
44.4
50
50
2900
37
5.5
125-200A
150
41.7
44
44
2900
30
5.5
125-200B
138
38.3
37.5
37.5
2900
22
5.5
125-250
160
44.4
80
80
2900
55
5.0
125-250A
150
41.7
70
70
2900
45
5.5

Application of centrifugal pump

  • Liquid transportation
  • Cooling system
  • Industrial cleaning system
  • Aquaculture farms
  • Fertilization system
  • Metering system 
  • Industrial equipment 

Centrifugal pump can be widely used in power, metallurgy, coal, building materials and other industries to transport slurry containing solid particles. Such as hydraulic ash removal in thermal power plant, slurry transportation in metallurgical concentrator, coal slurry and heavy medium transportation in coal washing plant, etc. When the centrifugal pump works, the pump needs to be placed on land, the suction pipe needs to be placed in water, and the pump needs to be filled and started. Due to the structural limitations of mud pump and submerged centrifugal pump, the motor needs to be placed on the water surface during operation, and the pump must be fixed, otherwise the motor will be scrapped if it falls into the water. Moreover, because the length of the long shaft is generally fixed, the installation and use of the pump is troublesome, and the application occasions are subject to many restrictions.

Working flow of centrifugal pump

Working point
The characteristic curve of centrifugal pump is the inherent characteristic of the pump itself, which has nothing to do with the external use. However, once the pump is arranged to work in a certain pipeline system, its actual working condition is not only related to the characteristics of the centrifugal pump itself, but also depends on the working characteristics of the pipeline. Therefore, to select and use the centrifugal pump well, we should also consider the characteristics of the pipeline at the same time.
When conveying liquid in a specific pipeline, the pressure head he required by the pipeline changes with the square of the flow QE. Drawing this relationship on the coordinate paper is the corresponding pipeline characteristic curve.
If the characteristic curve of the centrifugal pump and the characteristic curve of its pipeline are drawn on the same coordinate paper, as shown in the above figure, the intersection m of the two lines is called the working point of the pump. When selecting the pump, it is required that the flow and pressure head corresponding to the working point can not only meet the requirements of the pipeline system, but also be provided by the centrifugal pump, i.e. Q = Qe, H = He.
Flow regulation
(1) Change the opening of the valve
The essence of changing the valve switch on the outlet pipeline of centrifugal pump is to change the pipeline characteristic curve. As shown in the figure below, when the valve is closed, the local resistance of the pipeline increases, the pipeline characteristic curve becomes steeper, the working point moves from m to M1, and the flow decreases from QM to QM1. When the valve is opened, the pipeline resistance decreases, the pipeline characteristic curve becomes flat, the working point moves to M2, and the flow increases to QM2.
It is fast and convenient to adjust the flow with the valve, and the flow can change continuously, which is suitable for the characteristics of continuous chemical production. Therefore, it is widely used. The disadvantage is that when the valve is closed, the resistance loss increases and the energy consumption increases, which is very uneconomical.
(2) Change the speed of the pump
Changing the speed of the pump is essentially changing the characteristic curve of the pump. The original rotating speed of the pump is n and the working point is m, as shown in the figure below. If the rotating speed of the pump is increased to N1, the pump characteristic curve H-Q moves upward, the working point moves from m to M1, and the flow increases from QM to QM1. If the speed of the pump is reduced to N2, the working point is moved to M2 and the flow is reduced to QM2.
This regulation method requires variable speed device or expensive variable speed prime mover, and it is difficult to continuously regulate the flow, so it is rarely used in chemical production.

Standard for centrifugal pumps

In the field of petroleum and chemical industry, the international standards of centrifugal pumps most used are API610, ISO5199 and ANSI B73.1M/B73.2M, and the domestic standards are GB3215 and GB5656/T.
API610
API is the abbreviation of American Petroleum Institute. The purpose of API 610 standard is to provide a procurement specification for the manufacture and procurement of centrifugal pumps.
ISO5199
ISO is the abbreviation of the international organization for standardization. ISO5199 technical specification for centrifugal pumps, class II, mainly based on German DIN standards.
ASMEB73.1M/B73.2M
ASME is the abbreviation of American Society of mechanical engineers.

Cavitation and gas binding of centrifugal pump

Cavitation phenomenon

According to the working principle of centrifugal pump, when the liquid between blades is thrown out from the high-speed rotating impeller, a low-pressure area is formed near the impeller inlet. When the pressure at the inlet of the impeller is equal to or lower than the saturated vapor pressure PV of the transported liquid at the operating temperature, the liquid there will vaporize and produce bubbles. When the bubble flows to the high-pressure area with the liquid, the bubble condenses rapidly due to pressure.
At the moment of bubble condensation, a local vacuum will be generated, and the surrounding liquid will rush to the space originally occupied by the bubble at a high speed, causing impact and vibration, resulting in great impact force. Especially when the condensation point of bubbles is near the blade surface, many liquid particles impact the blade with high frequency and pressure; At the same time, a small amount of oxygen may be entrained in the bubble to chemically corrode the metal materials. Under the combined action of continuous impact and chemical corrosion, the surface of the blade is damaged and there are spots and cracks, which will lead to premature damage of the blade. This phenomenon is called cavitation of centrifugal pump.

cavitation phenomenon - What is a centrifugal pump

Gas binding phenomenon

When the centrifugal pump is started, if there is air in the pump, because the air density is very small and the centrifugal force generated after rotation is small, the low pressure formed in the central area of the impeller is not enough to suck in the liquid. In this way, although the centrifugal pump is started, it can not complete the transportation task. This phenomenon is called air binding.
This means that the centrifugal pump has no self-priming capacity, so the centrifugal pump must be filled with delivered liquid before starting. Of course, if the suction port of the centrifugal pump is placed below the liquid level of the transported liquid, the liquid will automatically flow into the pump, which is a special case. The suction pipeline of the centrifugal pump is equipped with a bottom valve to prevent the liquid filled before startup from flowing out of the pump. The filter screen can block the solid suction in the liquid and block the pipeline and the pump shell. The regulating valve installed in the discharge pipeline is used for starting the pump, stopping the pump and regulating the flow.
From the different causes of cavitation and gas binding:
Air binding is that there is air in the pump body, which generally occurs when the pump is started, mainly because the air in the pump body is not discharged completely; Cavitation is due to the vaporization pressure of the liquid at a certain temperature. It can be seen that it is closely related to the conveying medium and working conditions.
There are the following methods to prevent air binding:

  • 1. Fill the shell with liquid before startup. Do a good job in the sealing of the shell, the water filling valve and shower head shall not leak, and the sealing performance shall be good.
  • 2. The suction pipeline of the centrifugal pump is equipped with a bottom valve to prevent the liquid injected from flowing from the pump before startup. The screen prevents the suction of solids in the liquid. The discharge pipeline is equipped with a regulating valve, which is used for starting and stopping the pump and regulating the flow.
  • 3. Place the suction port of the centrifugal pump below the liquid level to be transported, and the liquid will automatically flow into the pump.

Causes and solutions of cavitation

The main causes of cavitation are:

  • 1. The resistance of inlet pipeline is too large or the pipeline is too thin
  • 2. The temperature of conveying medium is too high;
  • 3. The flow is too large, that is, the outlet valve is opened too much;
  • 4. The installation height is too high, which affects the liquid absorption of the pump;
  • 5. Selection, including pump selection, pump material selection, etc

Terms of settlement:

  • 1. Clean the foreign matters in the inlet pipeline to make the inlet unblocked, or increase the pipe diameter;
  • 2. Reduce the temperature of conveying medium;
  • 3. Reduce the installation height;
  • 4. Re select the pump, or improve some parts of the pump, such as selecting cavitation resistant materials.

Source: Network Arrangement – China Pipe Fitting Manufacturer – Yaang Pipe Industry (www.epowermetals.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

If you want to have more information about the article or you want to share your opinion with us, contact us at sales@epowermetals.com

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