There are multiple causes of cavitation in split case pumps, and there are also many corresponding treatment methods. The following will introduce two solutions to this problem based on fundamental design concepts. In fact, as long as the cavitation problem is properly addressed, the performance of the split case pump will already reach half of its ideal state.
The area where the inlet edge of the impeller blade is in close proximity to the front cover plate is the region where cavitation bubbles first form. This is mainly because the flow velocity in this area is relatively high, and the size of the turning radius directly affects the cavitation resistance of the centrifugal pump. Specifically:
When the turning radius is small, the flow velocity in the area where the inlet edge of the blade is close to the cover plate will increase accordingly, which accelerates the formation of cavitation bubbles;
When the turning radius of the front cover plate is large, the flow velocity of the blade in this area will decrease, thereby preventing the formation of cavitation bubbles.
Therefore, effectively increasing the turning radius of the front cover plate can significantly improve the cavitation resistance of the pump. At the same time, during the process of increasing the turning radius, the inlet width of the pump will also change accordingly, and this change also helps to further optimize the cavitation resistance of the centrifugal pump.
On the premise of keeping the inlet diameter of the impeller unchanged, the area of the inlet region can be adjusted by changing the size of the hub, thereby changing the flow velocity at the inlet and ultimately improving the cavitation performance. The specific optimization methods are as follows:
If design conditions permit, the hub diameter can be reduced during the design phase of the pump. This can effectively increase the inlet area of the liquid flow, thereby directly promoting the improvement of the cavitation resistance of the centrifugal pump;
Compared with the optimization method of increasing the inlet diameter of the impeller, reducing the hub diameter has a more significant effect on improving cavitation performance. It can more effectively reduce the occurrence rate of cavitation bubbles in the region with the largest inlet diameter of the impeller.
However, when adopting this solution, there is one point that requires special attention: the strength of the rotating shaft must be strictly controlled. Since the strength of the rotating shaft is directly related to its own diameter, when determining the reduction range of the hub diameter, the strength requirements of the shaft must be fully considered, and the value of the diameter reduction must be set reasonably to avoid affecting the overall operational stability of the pump due to insufficient shaft strength.
3.Glossary of Key Terms (for Clarity in Engineering Context)
Split Case Pump: A type of centrifugal pump with a horizontally split casing, widely used in industrial water supply, HVAC, and irrigation systems.
Cavitation: A phenomenon where low pressure in the pump causes liquid to vaporize (form bubbles); when bubbles collapse, they generate shockwaves that damage impeller surfaces and reduce pump efficiency.
Impeller: The rotating component that transfers energy to the liquid, consisting of blades, a front cover plate, and a hub.
Hub: The central part of the impeller that connects to the rotating shaft, through which the shaft drives the impeller.