Is there an ideal impeller vane number?
Randal FermanCentrifugal pump design and manufacturing has been around for over 200 years. If there were an ideal impeller vane number, it seems likely someone would have discovered it by now. However, just because an ideal vane number has not yet been established is not sufficient reason to consider it doesn’t exist.
Single stage pump and first stage, high suction performance impellers tend to have fewer vanes – often 3, 4 or 5. Multistage pump series stages, pipeline pumps and large, high efficiency pumps tend to have 7 or more impeller vanes. Vane number might be dictated by special application requirements. Such is the case with solids handling impellers which often have just 2 or 3 vanes and sometimes only 1.
I recall an anecdote I heard decades ago from a senior hydraulic engineer that only 3-vane impellers are found across the entire range of specific speeds. The problem, especially for high speed, high head pumps, is a 3-vane impeller produces significantly less head than, say, a 7-vane impeller. Head rise to shutoff and pressure pulsations are also issues.
But thinking about this quasi-factual anecdote, I’ve occasionally considered that an ideal vane number does indeed exist. If there is a magic vane number, what is it? If there could be only one impeller vane number for all pumps, what would it be? Pump engineers think these kinds of thoughts.
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37 comments
The flow rate demands of our pump have recently changed to a higher capacity. We have also had vibration issues (6x vane frequency). The suggestion on the table is to change the impeller to 7 vanes to help mitigate these issues. Do you feel that this is the right approach?
Thanks
Sofrani,
Good question. To economize on the radial dimensions or diameter of the pump casing, and in the interest of optimal performance, the desired hydraulic geometry of the diffuser typically demands a larger number of passageways compared to that of the mating impeller. To avoid excessive pressure pulsations and acoustic response from the interactions of impeller and diffuser flow fields, particularly with higher energy pumps, matching vane number combinations or their even multiples are definitely to be avoided. Certain even versus odd vane number combinations can also be undesirable depending upon the resulting beat frequencies.
Best regards,
Randal
Dear All,
Why the numbers of vanes in impellers shall be different to the numbers of vanes in diffusers?
Thanks,
Sofrani
Dear Chidi Cub,
The requirements for sand production are satisfied by selecting the appropriate dredge pump and its operating speed. The pump manufacturer chooses impeller vane number based on geometry that will satisfy solids handling requirements. Please refer to my comment reply posted Sept 19, 2014.
Regards,
Randal
Dear Randal
What effect does higher vane pumps has to the lower van pumps with respect to production in sand dredging.