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
Lizardo,
The question can be answered generally, but may not necessarily be correct for your specific pump. If only the vane number is reduced from 6 to 5, whether or not the vane design is changed, a reduction in pump head vs. flow can be expected, as well as reduction in torque and power. I might guess a drop of 10% – 15% head at a given rate of flow, but I wouldn’t wager any money on it. NPSHR is likely to improve, but this would be of no consequence if the existing 6-vane impeller already has adequate NPSH margin. The overall effect of this vane number change will also depend on the system characteristics. I hope this helps.
Randal
Dear Randal,
I find interesting your note. I have a question. If a pump is designed with a 6 vanes impeller, and for availability reasons during maintenance the pump is assembled with a 5 vane impeller, what is to expect in performance (flow, head, energy consumption, torque…)?
Thank you in advance for your comments.
Lizardo