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Centrifugal Pump System Efficiency Optimization

Aug 19,2025

Centrifugal Pump System Efficiency Optimization

Pumps have a wide range of applications and operate in large numbers, so they consume a lot of energy. 20% of the world's electricity consumption is used for pump operation. If the efficiency of each pump is increased by an average of 1%, a significant amount of current and fuel can be saved. Therefore, the efficiency of the water pump should be improved as much as possible.

Centrifugal pump (horizontal end suction centrifugal pump) efficiency is the ratio of the effective power N of the pump to the shaft power N. Due to various losses inside the pump, the effective power of the pump is always less than the shaft power, so the efficiency of the pump is always less than 1. The part of the effective power that is less than the shaft power is the loss inside the pump. Only by minimizing various losses inside the pump as much as possible can the efficiency of the pump be improved.

What are the losses of centrifugal pumps? Generally, it can be divided into mechanical loss, volume loss, and hydraulic loss.

Hydraulic Loss and Hydraulic Efficiency

Hydraulic loss is the more severe of the three types of losses. The hydraulic losses of pumps mainly include hydraulic friction losses and local losses.

Hydraulic friction refers to the loss caused by the friction between the liquid and the pump surface, as well as between liquids, due to viscosity, when liquid flows through a centrifugal pump.
Hydraulic friction increases with the increase of relative roughness. In production, there are often situations where the impeller or pressure chamber flow channel is not smooth, with burrs, burrs, or sand sticking, which reduces the pump's head and efficiency. Therefore, it is recommended to maintain a smooth impeller and pressure chamber flow channel to effectively improve the pump's operating efficiency.
The flow channel of various parts inside the centrifugal pump should not be too long, such as the flow channel formed by the impeller blades, guide vanes, etc. Excessive elongation will not only increase friction losses, but also bring difficulties to sand cleaning during casting.
The cross-section of the twisted blade inlet should not be too narrow. When drawing the blade, attention should be paid to the working surface of the impeller or guide vane inlet edge and the flow cross-section formed by the back of the adjacent impeller, which should not be too narrow, to avoid the relative speed being too fast and reducing the efficiency and suction capacity of the pump.

Local Loss

Local loss mainly refers to the local loss in the pipeline, which occurs in the area where the flow channel rapidly expands, contracts or turns, stagnant water zone, the direction of the flow channel is inconsistent with the direction of the liquid, and the convergence area of the liquid flow with different speeds.

The liquid generates vortices in the above-mentioned area, causing the liquid flow to impact, rotate, form friction, consume the energy of the liquid, and increase hydraulic losses.

Several points should be noted to reduce local losses:

The changes in the magnitude and direction of liquid flow velocity should be gentle to avoid rapid expansion, contraction, or turning of the flow channel.
The impeller blades or guide vanes should not be too thick. After considering the strength, corrosiveness, and possibility of casting, the impeller should be as thin as possible to avoid displacement at the inlet of the booster and expansion at the outlet.
The presence of stagnant water areas should be avoided throughout the entire flow channel.
Carefully select the inlet and outlet angles of the impeller blades and guide vanes.
Select appropriate flow rates for each section of the channel.

Mechanical Loss and Mechanical Efficiency

Mechanical loss refers to the power consumed by the friction loss of the pump's shaft seal, bearings, and impeller disc.

The mechanical losses of centrifugal pumps can also be divided into two types:

One is the mechanical friction loss between the bearings and shaft seals of the pump.
The other is the mechanical friction loss between the liquid and the rotor (i.e., disc friction loss)..

The friction loss in shaft seals and bearings is generally around 1% - 3% of the shaft power (1% for high-power pump areas and 3% for low-power pumps).
When it is necessary to understand the frictional power loss between the shaft seal and the bearing, the pump can be left empty and the power consumed by the pump during idle operation can be measured. This power is the frictional power loss between the shaft seal and the bearing.
At present, many pumps generally use mechanical seal structures, which actually result in much smaller friction losses for shaft seals compared to packing seals.
When using a packing sealing structure, if the packing gland is pressed too tightly, friction loss will increase, and it may become hot and burned out

Disc Friction Loss

When the impeller of a centrifugal pump rotates inside a pump filled with liquid, there is frictional loss between the outer surface of the impeller and the liquid.

Disc friction loss accounts for a relatively large proportion of mechanical losses, especially for centrifugal pumps with medium and low specific speeds, where disc friction loss is more severe. Compared to centrifugal pumps with high specific speeds, disc friction loss accounts for a smaller proportion.

The magnitude of the power loss caused by the friction between the impeller and the disc is proportional to the third power of the rotational speed and the fifth power of the outer diameter of the impeller. The larger the outer diameter of the impeller, the greater the friction loss of the disc. Disc friction loss is the main reason for the decrease in efficiency of low specific speed centrifugal pumps. Therefore, under the condition of constant pump speed and flow rate, increasing the impeller outer diameter to increase the head of a single-stage pump is accompanied by a sharp increase in disc friction loss.

The friction loss of the disc is proportional to the third power of the rotational speed. On the other hand, for a given head, as the pump speed increases, the impeller diameter decreases accordingly (it can be considered that as the pump speed increases, the outer diameter of the impeller decreases by half). However, as the outer diameter of the impeller decreases, the friction loss of the disc decreases proportionally to the fifth power. Therefore, for a given head, as the centrifugal pump speed increases, the friction loss of the disc may not necessarily increase, but may decrease. This is also one of the factors that gradually increase the rotational speed of the pump.

The size of disc friction loss is related to the surface roughness of the impeller cover plate and the inner wall of the pump body. Reducing the surface roughness can reduce the disc friction loss of the impeller.

The experiment shows that:

After spraying the rough surface of the cast iron pump body, the efficiency of the pump can be improved by 2% - 3% compared to before spraying.
After grinding the rough surface of the impeller cover plate and pump body with a grinding wheel, the efficiency of the pump can be improved by 2% - 4%.

The power loss caused by the friction of the impeller disc is also related to the size of the side clearance between the impeller and the pump body. For general centrifugal pumps, the friction loss of the impeller disc is relatively small within the range of 2% - 5%.

Volume Loss and Volume Efficiency

When the pump is running, the pressure of the liquid inside the pump body is uneven, with high and low pressure zones. Due to structural requirements, there are many gaps inside the pump. When the pressure before and after the gaps is uneven, the liquid needs to flow from the high pressure zone to the low pressure zone. This part of the liquid flows back to the low pressure zone from the high pressure zone, which is not effectively utilized by the impeller and circulates inside the pump body. This energy loss is called volume loss.

Due to a portion of the liquid flowing out of the impeller returning to the pump and not being discharged outside, the actual discharge flow rate of the pump is smaller than the flow rate through the impeller.

In general centrifugal pumps, there are mechanisms for balancing axial force, such as balance holes and balance disks. Although some liquid obtains energy from the impeller, it is not effectively utilized and consumed to overcome the resistance of the balance mechanism. These energy losses also belong to volume losses. Generally, the presence of balance holes reduces pump efficiency by 3% - 6%.

For a given pump, to improve volumetric efficiency and reduce leakage, the following measures can be taken:Reduce the annular area of the sealing gap. Under the condition of a direct point at the impeller inlet, the average value of the sealing gap should be minimized as much as possible. On the premise of ensuring safe operation and manufacturing commitments, a smaller gap width should be selected.

Experiments have shown that when the gap width of the sealing ring is reduced from 0.5 millimeters to 0.3 millimeters, the pump efficiency increases by 4% - 4.5%.

Centrifugal Pump Motor Efficiency

The efficiency of centrifugal pump motor is a measure of the effectiveness of the motor in converting input electrical energy into mechanical energy, which directly affects the overall efficiency and energy consumption economy of the water pump system.

The efficiency of ordinary motors is usually 75% - 95%. High efficiency motors (IE4/IE5 standards) can reach 90% - 96%.

Main Factors Affecting Motor Efficiency

Load Matching: The motor has the highest efficiency at 75% to 100% of the rated load, and the efficiency significantly decreases at light loads (<50%).
Motor Type:
- Asynchronous motor: Low efficiency (IE1-IE3 standards).
- Permanent magnet synchronous motor: Higher efficiency (up to IE4/IE5 standards), especially suitable for variable frequency working conditions.
Design and Materials: The high-efficiency motor adopts low loss silicon steel sheets, optimizes winding design, and reduces mechanical friction (such as high-quality bearings).
Operating Environment: High temperature, unbalanced voltage, or frequency fluctuations can reduce efficiency.

System Efficiency

Total pump efficiency = Motor efficiency × Pump hydraulic efficiency × Transmission efficiency (low motor efficiency can lead to increased overall energy consumption).

Variable Frequency Regulation

The frequency converter can optimize the motor speed to match the load, but it has a loss of 2% to 5%, and the energy-saving effect needs to be balanced.

Efficiency Improvement Measures

Selection Optimization: Choose IE3/IE4 high-efficiency motors to avoid "big horses pulling small cars".
Maintenance: Regularly lubricate bearings, check winding insulation, and maintain good heat dissipation.
Intelligent Control: Install a frequency converter (for variable flow conditions) to achieve soft start and dynamic speed regulation.

The price of high-efficiency motors is 10% - 30% higher, but the long-term energy-saving benefits are usually recovered within 1-3 years.

The energy consumption of the motor accounts for more than 60% of the total cost of the pump system, and the efficiency improvement of 1% can save considerable electricity costs annually.

Water pressure efficiency formula:

Hydraulic Efficiency Formula

ρ: Fluid density (kg/m³, water ≈ 1000)
g: Gravity acceleration (9.81m/s²)
Q: Actual flow rate (m³/s)
H: Actual head (m)
P-axis: Pump shaft input power (W)

Calculation example
Transport of fluids:Clear water(P=1000kg/m³)

Head H=30m
Axial power P Axial =15kw=15000w
Input electrical power P Axial=18kw=18000w

Water pump

1.Calculate the water pressure power：

P Waterpressure=pgqh=1000x9.81x0.0277x30=8152.11w
2.Water pressure efficiency：

3.Overall efficiency:

4.Mechanical efficiency:

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