How To Optimize The Design Of Centrifugal Pump Impeller

Jan 21, 2026

If you want to optimize the design of centrifugal pump impellers. Therefore, it is necessary to clarify the purpose of optimization: to improve inhalation performance? Improve the efficiency of the pump? Adjust the rise amplitude of the Q-H curve... and then optimize it according to specific needs. The main hydraulic component that affects the performance of centrifugal pumps is the impeller, in addition to the flow components such as volutes/guide vanes that are matched with it.
Fluid mechanics is a semi theoretical and semi empirical discipline, and there are still many areas that cannot be accurately designed, simulated, and predicted, such as the inability to accurately simulate the true flow state of fluids and their impact on pump performance under different structures, temperatures, and pumping media. Therefore, this article can only briefly explain how to optimize the impeller of a centrifugal pump to improve its suction and hydraulic performance from a qualitative perspective, combined with experience. For reference only.

 

1. Improve inhalation performance

There are two types of bending for impeller blades: forward bending and backward bending. Due to its effectiveness in maximizing power, imparting high rotational force to the fluid, and preventing flow separation, centrifugal pumps typically use rear curved blade impellers.
For the pump body, the cavitation behavior and suction performance of the pump are largely influenced by the geometric shape and area of the impeller inlet. Many geometric factors at the inlet of the impeller can affect cavitation, such as inlet and hub diameter, blade inlet angle and upstream flow incidence angle, blade number and thickness, blade throat area, surface roughness, blade leading edge profile, etc. In addition, it is also related to the outer diameter of the impeller blades and the gap size between the guide vanes (for guide vane pumps) or volutes (for volute pumps).

1) Inlet diameter/inlet area of impeller

In order to improve the suction performance of centrifugal pumps, designers generally achieve this by increasing the inlet diameter of the impeller. Today, this design method is still being used in the engineering design of centrifugal pumps.
When the shaft diameter is the same and the diameter clearance at the impeller mouth ring is the same, the better the suction performance (the larger the impeller inlet area, the higher the suction specific speed value), the larger the clearance area at the impeller mouth ring, which means that the leakage amount is greater and the pump efficiency is lower.
However, for the method of improving suction performance by increasing the inlet diameter of the impeller, special attention must be paid to:
It is not allowed to cause the suction specific speed value to significantly exceed the values specified in relevant standards and specifications, otherwise it will result in a narrow stable operating range of the pump.

2) Blade leading edge shape

Satisfying the mechanical and manufacturing constraints of the leading edge blade thickness, adopting a parabolic profile can improve the suction performance of the impeller. The suction performance of the elliptical contour is second, and this shape is the default contour selection for the leading edge, as it can easily meet the mechanical and manufacturing limitations of the blade leading edge thickness.

 

3) The curvature radius of the inlet part of the impeller cover plate

Due to the centrifugal force acting on the liquid flow at the inlet of the impeller at the turning point, the pressure is low and the flow velocity is high near the front cover plate, resulting in uneven velocity distribution at the inlet of the impeller. Appropriately increasing the curvature radius of the inlet part of the cover plate is beneficial for reducing the absolute velocity at the front cover plate (slightly ahead of the blade inlet) and improving the uniformity of velocity distribution, reducing the pressure drop at the pump inlet part, thereby reducing NPSHR and improving the anti cavitation performance of the pump.

4) Position of blade inlet edge and shape of inlet part

The inlet edge of the blade extends laterally towards the suction port, using a swept back blade inlet edge (the inlet edge is not on the same axis, and the outer edge is offset by a certain angle backwards), which allows the liquid flow on the hub side to receive the action of the blade in advance and increase pressure.
The inlet edge of the blade extends forward and tilts, causing different circumferential velocities at each point. Generally, the axial velocity is distributed approximately uniformly along the inlet edge, resulting in different relative flow angles at each point on the inlet edge. In order to meet this flow situation and reduce impact losses, the blade inlet should be made into a spatially twisted shape, which is why many low-speed impeller blade inlet parts are also made into twisted blades.

5) Blade inlet angle

The design condition adopts a slightly larger positive angle of attack to increase the inlet angle of the blades, reduce the bending at the inlet of the blades, reduce the displacement of the blades, increase the inlet flow area of the blades, and thus improve the suction performance. At the same time, it will also improve the operating environment under high traffic to reduce traffic losses. However, the angle of attack should not be too large, otherwise it will affect efficiency.

6) Blade inlet thickness and smoothness

Reduce the thickness of the blade inlet appropriately and round it to make it closer to a streamlined shape. Reducing blade thickness not only expands the area of the impeller suction channel, reduces flow velocity, and increases pressure (the shape of the blade inlet is highly sensitive to pressure drop), but also improves the surface smoothness of the impeller and blade inlet, reducing resistance losses. These measures are all beneficial for improving the suction performance of the pump.

7) Balance hole

The balance hole on the impeller has a certain destructive effect on the main flow entering the impeller due to leakage (the area of the balance hole should not be less than 5 times the sealing gap area to reduce the leakage flow rate and thus minimize the impact on the main flow). Research has shown that when a balance hole is opened on the impeller, the vortex intensity behind the impeller will decrease, and some vortices may even disappear, improving the suction performance of the pump.

8) Impeller outlet diameter

A small decrease in impeller diameter will only slightly increase NPSHR. But when the diameter decreases by 5% to 10%, NPSHR will significantly increase, because the reduction in blade length will increase specific blade loads, thereby affecting the velocity distribution at the inlet of the impeller.

Notes:

1) Try to avoid using the method of increasing the inlet area of the impeller to improve the suction performance, and avoid severely exceeding the suction specific speed, otherwise it is easy to cause inlet reflux and expand the unstable operating area of the pump.
2) The occurrence of blade channel syndrome cavitation should be avoided. This type of cavitation damage is caused by the small gap between the guide vanes (for guide vane pumps) or volutes (for volute pumps) and the outer diameter of the impeller blades. When the liquid flows through the small channel, the increase in liquid velocity causes a decrease in liquid pressure, local vaporization, and the generation of bubbles, which then rupture at higher pressures, leading to cavitation.

 

2. Improve hydraulic performance

There are many factors that affect the hydraulic performance of pumps, and the main factors that affect the hydraulic efficiency of impellers are various losses. Specifically, there are:
 

1) Number of leaves

For centrifugal pumps, increasing the number of blades can generally improve the flow of liquid and increase the pump head appropriately. However, increasing the number of blades will reduce the flow area of the channel, leading to an increase in flow velocity and friction loss of the blades.

 

 

Therefore, excessive increase in the number of blades not only reduces efficiency and deteriorates the cavitation performance of the impeller, but may also cause a hump in the pump performance curve. In addition, an increase in the number of blades will flatten the upward trend of the head characteristic curve (from the rated point) to the critical dead point; On the contrary, as the number of blades decreases, the head characteristic curve becomes steeper. Usually, 5-7 blades are selected for centrifugal pump impellers with a large number of blades.
 

2) Long and short leaves

Research has shown that any combination of short and long blades in a pump impeller will be beneficial for improving pump efficiency, as it can effectively prevent any development of wake flow caused by uneven velocity distribution near the impeller inlet.
 

3) Twisted blades

Experiments have shown that pumps with twisted blades have higher efficiency near the design operating point and in high flow areas compared to pumps with curved blades. At the same time, pumps with twisted blades have a higher head at the critical point than those with curved blades (which can change the upward trend of the head characteristic curve at the critical point, especially for low specific speed centrifugal pumps, which can effectively improve/eliminate humps).

4) Impeller outlet diameter

The API 610 standard does not allow pumps to reach the maximum impeller diameter and requires cutting the impeller to meet the required performance of the pump. If the pump selection is too large, cutting the impeller is a relatively economical and effective method to reduce the pressure and flow generated. Although cutting the impeller is more efficient than using a throttle valve to meet the required operating conditions, its efficiency is usually lower than that of a full-size impeller because the impeller blades are shortened and the gap between the impeller blades and the pump housing increases.
For radial flow impellers, their diameter should not be reduced to more than 70% of the maximum design diameter. The reduction of pump impeller diameter will also change the outlet channel width, blade outlet angle, and blade length. The more the impeller diameter decreases from the maximum diameter, the more the pump efficiency will decrease with the cutting of the impeller, and the highest efficiency point will shift towards lower flow rates.

3. The influence of other parameters on pump performance

 

1) Blade width of impeller

As the blade width increases, the liquid pressure decreases, so the head will decrease with the increase of impeller blade width; The effect of blade width on the efficiency of the optimal efficiency point is usually not significant (as the blade width increases, the efficiency of the optimal efficiency point may slightly increase), but the high-efficiency zone will shift towards lower flow rates as the blade width decreases. The impact of efficiency is more significant at larger volumetric flow rates, in other words, as the blade width increases, the efficiency curve rapidly decreases to the right of the optimal efficiency point.
 

2) Impeller outlet blade angle

The larger the outlet blade angle, the higher the head at a given speed, but at the cost of lower efficiency and wear performance. The lower outlet blade angle increases efficiency and blade length, but at the cost of reducing head. Therefore, the export blade angle usually needs to be optimized to achieve a balance of these factors. The head increases with the increase of outlet blade angle, which can be explained by the increase in outlet cross-sectional size relative to the increased outlet blade angle, resulting in a decrease in liquid pressure drop in the flow channel between the blades.

 

 

The study suggests that the maximum efficiency value decreases with the increase of the outlet blade angle. When the outlet blade angle is small, the efficiency of the pump on the right side of the highest efficiency point will rapidly decrease.

3) Impeller outlet splitter blade

Adding splitter blades on the outlet side of the impeller will increase the pump's head and hydraulic efficiency, and the increase in head and efficiency will be greater as the length of the splitter blades increases. The length of the splitter blades usually does not exceed 0.5 times the original blade length, depending on the size of the impeller, the shape of the blades, and the number of blades.

4) Trimming of impeller blade outlet edge

Grinding the back of the impeller outlet blades expands the flow channel area of the impeller outlet, thereby increasing the flow rate of the impeller. As the outlet channel area expands, the head will also increase, and the optimal efficiency point of the pump will shift towards the high flow side.