Questions about the closed impeller of centrifugal pumps
Thread Content
I have a question for the more experienced colleagues: 1. On-site, I noticed that the diameter of the impeller blades in a centrifugal pump was different from the diameter of the cover plate; previously, I had seen them to be of the same size. So, if the diameter of the blade decreases while the diameter of the cover plate remains unchanged, how will the flow rate and head under these conditions compare to those when the impeller cover plate had its original size? 2. I heard before that impeller cutting is used; could it be that only the blades are cut while the shroud remains untouched? If that’s the case, then why not cut the cover plate as well? Personally, I think it would be more convenient to machine everything together, including the cover plate. Thirdly, if for impeller A only the blade diameter is reduced while the diameter of the cover plate remains unchanged, compared to impeller B where both the blade diameter and the cover plate diameter are reduced (so that the blade diameters of both impellers are the same), will the flow rate and head be identical?
Blade cutting is done solely to improve efficiency; this cutting method is generally employed for the impellers of multi-stage pumps with radial vanes
The flow rate and head will also change depending on the blade
If the diameter of the cover plate is also cut, it will change the dynamic balance characteristics of the impeller. Another issue is flow guidance; turbulence occurs as water exits the impeller, which affects efficiency.
Thank you all for your replies. I seem to understand a bit now, but I still don’t get questions 1, 2, and 3:(
Won’t the flow rate decrease when the blade is cut smaller? How can we understand that efficiency has improved?
It is mainly the efficiency affected by internal backflow
1. After the blade is cut, the flow rate decreases and the head drops. 2. There are two different cutting methods; cutting only the blades does indeed make the process a bit more complicated, but the reduction in head pressure is less than that resulting from cutting the impeller, and the overall outcome is better. 3. It’s impossible for them to be exactly the same; under identical conditions, the head and flow rate of the blades cut will be slightly higher.