Table of Content

What is the centrifugal pump performance curve
Types of pump performance curves
Flat performance curves
Steep performance curve
Performance curve with a hump
How to read centrifugal pump performance curve

What is the centrifugal pump performance curve?

The centrifugal pump performance curve is a graph indicating the value of the centrifugal pump basic performance parameters such as head, power, efficiency, flow rate and their interrelationship when the pump is running at a certain speed, different speed, the graph is not the same

The Centrifugal pump performance curve expresses the trend of the value change of another parameter of the pump under the condition that one parameter of the pump is determined and other working conditions are the same. The shape of the performance curve also reflects the characteristics of the pump, based on the shape of the curve, the pump can be selected to suit the characteristics of the process; the pump performance curve can also be applied to determine the pump's operating point. Flow and head Q an H curve, flow and power Q a P curve, flow, and efficiency Q-η curve, differential pressure and flow ΔP-Q curve, differential pressure and power ΔP-P curve, differential pressure, and efficiency ΔP-η curve, etc. The pump performance curves are generally obtained from the pump performance test. The expected performance curve can be obtained by calculation when the pump is designed, and the pump needs to be verified by a water test after it is made.

Types of pump performance curves

Flat performance curves

This performance curve is suitable for a wide range of flow adjustments, while the pressure requirements of small changes in the system. For example, the need to adjust the flow with a regulating valve, but must maintain a certain liquid level or a certain pressure in the system (such as boiler feed pump), the use of a flat performance curve of the pump can play a role in a certain range of automatic maintenance of the liquid level and pressure

Steep performance curve

This performance curve is suitable for systems that require a large change in the head when the flow rate does not change much, or systems that require a small change in flow rate when the head fluctuates. For example, in the system of transporting fiber slurry, in order to avoid blockage of fiber slurry in the pipeline when the flow rate slows down, that is, we hope that no matter how much the resistance in the pipeline system increases, and the flow rate (flow rate) does not change much, therefore, it is more appropriate to use the pump with steep drop performance.

Performance curve with hump

Pumps with such curves may appear unstable conditions in the process of operation. Pump operating condition point by the pump performance curve and device performance curve intersection to determine, but the pump performance curve with a hump often intersects with the pump device characteristics curve in two points, so that the pump in unstable conditions, affecting the safe operation of the pump. Therefore, the performance curve of the hump, the general provisions of the working point head must be less than the shutdown head (the export valve is closed, the flow rate is equal to zero head), so as to avoid the pump in unstable operating conditions

Commonly used methods for eliminating humps in performance curves

Reducing the blade exit angle, a flat declining performance curve can be obtained, thus eliminating the hump

Make the liquid into the impeller has pre-spin, so that can contribute to obtaining a fully declined performance curve. After the liquid has pre-spin, the performance curve of the pump's large flow area decreases. With a semi-spiral suction chamber pump, the liquid also has pre-spin when entering the impeller, so the pump performance curve also has the same phenomenon. Although there is a pre-spin that can contribute to obtaining a completely declining performance curve, the negative effect is that the pump head is reduced.

The area of the pump pressure chamber (including the inlet of the vortex chamber and the guide vane) not only affects the size of the shut-off head but also affects the shape of the pump performance curve. The reduction in the area of the extrusion chamber can slightly increase the shut-off head of the pump, make the performance curve steeper, and move the optimal operating point to the direction of small flow; increasing the area of the extrusion chamber can slightly reduce the shut-off head. Make the performance curve flat, and move the best operating point to the direction of large flow. However, it should be noted that excessively increasing or reducing the inlet area of the press-out chamber will cause the pump efficiency to decrease;

Eliminate the hump in the curve by using the method of beveling the impeller outer diameter so that the difference between the front and rear flow line lengths is reduced;

How to read centrifugal pump performance curve

Centrifugal Pump curves show 4 important factors that are critical in selecting the right pump for your application

The Pump curve shows the Flowrate range on the x-axis. The first point on the curve at zero flow is referred to as “Shut Off” ( This is the head that occurs when the pump is running with the valve closed) and the last point at maximum flow is “Run Out”

The Pump curve shows the head, power, efficiency, and NPSH(r) range on the y-axis

As shown in the picture

When the flow rate and head are given, the feet of the corresponding values on the x-axis and y-axis are the rated operating points of the pump, and the other corresponding parameters can be determined successively

When choosing the pump model, we should consider all parameters to meet the working conditions, and usually choose to use the flow rate of the centrifugal pump for the best efficiency point corresponding to 70% to 120% of the flow rate, which will make the pump life longer and lower power consumption.

Water is the source of life
The pump brings water to where it is needed
Diesel engine water pumps are ideal for working in situations where electricity is unavailable or may be interrupted
This diesel engine irrigation water pump from An pump machinery, help our customer irrigation their fields.

Although this is a small project for us, we still take the big project as seriously as it is. Irrigation pump system designers still consider many factors, of which 3 main factors are as follows:

  1. Pressure on the irrigation system
    The design purpose of the irrigation system is to provide the correct amount of water to maintain the vitality of the plants, so it is necessary to consider whether the customer's irrigation method is watering or drip irrigation. The two methods have different requirements for the pump outlet pressure. The role of the pump in the irrigation system is very important. , Pressure is an important consideration for pumps
  2. Flow rate and head of irrigation pump
    When calculating the required head, it is necessary to consider the pipe damage to ensure that the pressure at the spray gun of the irrigation system is sufficient. When calculating the flow rate, it is necessary to meet the requirements of the customer and complete the irrigation task within a certain period of time.
  3. Client's budget
    Different budgets will result in different design schemes for the irrigation system. The irrigation system design engineer of Anpun Machinery will design the most reasonable irrigation system according to the customer's budget and irrigation requirements to meet customer needs and save costs for customers .

The basic parameters of a centrifugal pump include the pump
Flow rate
Head
Speed
Shaft power
Efficiency
NPSH

Flow rate

The flow rate of centrifugal pumps is divided into volume flow rate and mass flow rate
Hugh volume flow is the volume of liquid pumped by the pump in a unit of time, that is, the volume of liquid discharged from the pressure outlet section of the pump. Volume flow is expressed in Q, and its unit is cubic meters per hour (m3/h).
Mass flow is the mass of liquid pumped per unit of time, mass flow q, the unit of tons per hour (t / h). Engineering customary use t/h as a unit.
The flow rate of the pump is usually referred to as volume flow, only in rare cases to use the mass flow rate.
The relationship between the volume flow rate of the pump Q mass flow rate q is:

The term head is used instead of pressure in the centrifugal pump business. refers to the energy obtained by the single weight fluid through the pump.

The head of the pump depends on the structure of the pump (such as the diameter of the impeller, the bending of the blades, etc., and the speed. At present, the pressure head of the pump cannot be calculated theoretically. Generally, the experimental method can be used to determine the head of the pump. The experimental measurement is to install a vacuum gauge at the inlet of the pump and a pressure gauge at the outlet. If the kinetic energy difference between the two gauge sections (Δu2/2g=0) is not counted, the energy loss between the two gauge sections (∑f1-2 =0).
Pay attention to the following two points:
(1) where p2 is the reading of the pressure gauge at the outlet of the pump (Pa); p1 is the reading of the vacuum gauge at the inlet of the pump (negative gauge pressure, Pa).
(2) Pay attention to distinguish the two different concepts of centrifugal pump head (pressure head) and lifting height.

Rotating speed

The speed of the pump refers to the number of revolutions of the pump rotor per unit time. The speed of the pump is represented by n, and its unit is revolutions per minute (r/min) or revolutions per second (r/s).
Rotation speed can also be expressed by the rotational angular speed O of the rotor, its unit is per second (1/s), and the relationship between rotation speed and angular speed is

Shaft power

The work given to the pump shaft by the prime mover per unit of time is called shaft power, and the shaft transmits the power (motor power) to the power parts (impeller), and the power value is less than the rated power of the motor.

Efficiency

Pump in the process of transporting liquid, shaft power is greater than the power obtained from the impeller of the liquid discharged to the pipeline, because the volume loss, hydraulic losses mechanical losses are to consume part of the power, and the efficiency of centrifugal pump that reflects the pump to the extent of the use of external energy.
Pump efficiency value and the type of pump, size, structure, manufacturing accuracy, and the nature of the transported liquid related. Large pump efficiency value is higher, small pump efficiency value is lower.

NPSH

When the pump is working, the liquid will generate the gas at the inlet of the impeller due to certain vacuum pressure. The vaporized bubbles will degrade the impeller and other metal surfaces under the impact movement of the liquid particles, thereby destroying the impeller and other metals. At this time, the vacuum pressure is called vaporization. Pressure, net positive suction head refers to the excess energy that exceeds the vaporization pressure per unit weight of liquid at the suction port of the pump

Each centrifugal pump is composed of hundreds of parts, and the basic structure of the centrifugal pump is composed of six parts.
Impeller
Volute Casing
Shaft
Bearing
Seal ring
Stuffing box
These components can be subdivided into the wet end and mechanical end.

Impeller

The impeller is the core part of the centrifugal pump, it has high speed and high output, the impeller on the blade and plays a major role, the impeller should pass the static balance test before assembly. The inner and outer surfaces on the impeller are required to be smooth to reduce the friction loss of water flow.

The impeller can be generally divided into single-suction and double-suction two kinds, single-suction impeller for single-sided suction, small flow pump impeller is mostly this type. Double-suction impeller is two-sided suction, large flow pump impeller are used double-suction impeller

Impeller design is the most important factor in determining the performance of a centrifugal pump. A properly designed impeller optimizes the flow rate. Centrifugal pump type water pump impeller mainly has the following 3 forms, closed type, semi-open type, open type

Closed impeller: It consists of blades and front and rear cover plates. The closed impeller is more efficient and more difficult to manufacture. It is the most used in centrifugal pumps. Suitable for conveying clean water, solutions, and other clean liquids with small viscosity and no particles.

Semi-open impeller: there are two general structures one is the front semi-open, by the back cover and blade composition, this structure impeller efficiency is low, in order to improve efficiency need to be equipped with adjustable gap sealing ring another for the back semi-open, by the front cover and blade composition, because can be applied with the closed pump impeller the same sealing ring? Efficiency and closed impeller are basically the same, and the blade in addition to conveying liquid, but also has: back blade or vice impeller sealing role. The semi-open impeller is suitable for conveying liquids containing solid particles, fibers, and other suspended matters. The semi-open impeller is less difficult to manufacture, lower cost, and is adaptable, in recent years in the refinery chemical centrifugal pump application gradually increased, and used to transport clear water and near clearwater liquid

Open impeller: only the blade and blade reinforcement, no front and rear cover impeller. The number of open impeller blades is less than 2-5 pieces. Water pump impeller efficiency is low, the application is less, mainly used for conveying high viscosity liquid and slurry liquid.

Volute Casing

Acts as a support fixation and is connected to the bracket where the bearing is mounted

Shaft

The impeller mounted on the shaft, the pump shaft is connected to the motor by coupling and transmits the torque of the motor to the impeller, so it is the main part for transmitting mechanical energy.

Bearing

Bearings constrain the relative motion of the shaft (rotor) and reduce friction between the rotating shaft and the stator

Seal ring

Sealing rings are also known as leak reduction rings prevent the leakage of the pumped liquid

Stuffing box

The stuffing box is mainly composed of packing, water seal ring, packing cylinder, packing gland and water seal tube. The function of the stuffing box is mainly to close the gap between the pump casing and the pump shaft, so that the water inside the pump will not flow outside and the air outside will not enter the pump. Always keep the vacuum inside the pump! When the pump shaft and the packing friction heat will rely on the water seal tube water to the water seal ring to make the packing cool! Keep the normal operation of the pump. Therefore, we should pay special attention to the checking of the stuffing box during the operation tour of the pump! The packing should be replaced in about 600 hours of operation.

Table of Content

Centrifugal pump definition
Centrifugal pump basic structure
The working principle of centrifugal pump
Working process of centrifugal pump
Classification of centrifugal pumps
Centrifugal pump technical parameters
Centrifugal Pump Benefits

Centrifugal pump definition

Centrifugal pumps refer to pumps that rely on the centrifugal force generated when the impeller rotates to transport liquids, and the energy for impeller rotation usually comes from diesel engines or electric motors. Applicable to various industries, such as industrial applications agricultural irrigation, municipal water supply, power station circulation water supply, urban pollution treatment, etc.

Centrifugal pump basic structure

The basic components of a centrifugal pump are a high-speed rotating impeller and a fixed worm-shaped pump casing. The impeller is fastened to the pump shaft and driven by the pump shaft with the motor or diesel engine for high-speed rotation (also see centrifugal pump parts)
The impeller is the part that does work directly on the liquid in the pump and is the energy supply device of the centrifugal pump. The suction port in the center of the pump casing is connected with the suction pipeline, and the bottom of the suction pipeline is equipped with a one-way bottom valve. The discharge port at the side of the pump casing is connected to the discharge pipeline with a regulating valve.

The working principle of centrifugal pump

Centrifugal pump in the work, relying on high-speed rotation of the impeller, the liquid in the role of inertial centrifugal force gained energy to improve the pressure. Centrifugal pump in the work before the pump body and inlet pipeline must be full of liquid media, to prevent cavitation phenomenon. When the impeller rotates rapidly, the vane prompts the medium to rotate quickly, and the rotating medium flies out of the impeller under the action of centrifugal force, and the water inside the pump is thrown out after the central part of the impeller forms a vacuum area. One side constantly inhales the liquid, and the other side constantly gives a certain amount of energy to the inhaled liquid and discharges the liquid

Working process of centrifugal pump

Before starting the pump, fill the pump with the liquid to be delivered
After the pump is turned on, the pump shaft drives the impeller to rotate at a high speed to generate centrifugal force. Under this action, the liquid is thrown from the center of the impeller to the outer periphery of the impeller, the pressure increases, and flows into the pump casing at a very high speed.
Due to the continuous expansion of the flow channel in the volute pump casing, the flow rate of the liquid slows down, so that most of the kinetic energy is converted into pressure energy. Finally, the liquid flows into the discharge pipe from the discharge port with a higher static pressure
After the liquid in the pump is thrown out, a vacuum is formed in the center of the impeller. Under the action of the pressure difference between the liquid surface pressure (atmospheric pressure) and the pressure in the pump (negative pressure), the liquid enters the pump through the suction pipe to fill the gap. Where to drain the liquid

Classification of centrifugal pumps

Centrifugal pumps are classified in various ways, including by working pressure, by a number of working impellers, by way of impeller intake, etc.

According to working pressure

Low-pressure pumps: pressures below 100 m water column
Medium pressure pump: pressure between 100 and 650 m water column
High-pressure pump: pressure higher than 650 m water column

By number of working impeller

Single-stage pumps: only one impeller on the pump shaft
Multi-stage pump: There are two or more impellers on the pump shaft when the total head of the pump is the sum of the heads produced by n impellers

By impeller inlet method

Single side inlet pump: also called single suction pump, there is only one inlet on the impeller
Double-side inlet pump: also called double-suction pump, that is, there is a water inlet on both sides of the impeller. Its flow rate is twice as large as that of single suction pumps, which can be approximated as two single suction pump impellers placed back to back.

By pump shaft position

Horizontal pumps: pump shaft in a horizontal position
Vertical pump: the pump shaft is located in a vertical position

According to the medium conveyed by the centrifugal pump

Clean water pumps
Sewage pumps
Slurry pumps

By installation height

Self-priming centrifugal pump: the pump shaft is lower than the surface of the suction pool, no need to irrigate when starting, it can start automatically
Suction centrifugal pump (non-self-irrigating centrifugal pump): the pump shaft is higher than the surface of the suction pool. Before starting, it is necessary to fill the pump casing and suction pipe with water, then drive the motor to make the impeller rotate at high speed, the water is thrown out of the impeller by the centrifugal force, the negative pressure is formed in the center of the impeller, the water in the suction pool enters the impeller under the action of atmospheric pressure, and is thrown out of the impeller into the water pressure pipe by the action of the impeller rotating at high speed.

Special construction

The pipeline pump is installed as part of the pipeline without changing the pipeline
Submersible pump and motor are submerged in water as one unit
The submerged pump body is immersed in liquid

Centrifugal pump technical parameters

Pump Terms Glossary

Flow Rate
Head
Pumping liquid temperature range
System pressure
Shaft Power

Centrifugal Pump Benefits

Compact construction
Wide range of flow and head
Suitable for mildly corrosive liquids
Multiple control options
Uniform flow rate, smooth operation, and low vibration No special vibration-damping foundation is required
Low equipment installation, maintenance, and overhaul costs

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