Impeller with staggered vanes



Q  -  I noticed that in some large double-suction impellers the center rib (or center
shroud) extends all the way to the impeller outside diameter (OD), and the vanes
on both sides of the outlet do not line up.

In most double suction impellers the center rib extends only to about halfway of
the OD, and the impeller vanes line up at the outlet.

What are the reasons for this difference in impeller design?



A  -  We can give two reasons why some impellers are designed with full center
rib and staggered vanes:

One, a full center rib improves the structural integrity of the impeller vanes in high
speed or high pressure service, or in high specific speed design where the width
of the impeller vanes is wide. Without a full center rib, the vanes are at risk of
developing cracks.

Two, it allows the left hand (LH) vanes to be staggered from the right hand (RH)
vanes so that only half the vane width passes the volute lips at a time. It diffuses
the energy being imparted by the vanes to the volute lips and minimizes the
vibration induced by the impeller vane/volute lip interaction.

The downside to the full center rib design is that the pump efficiency is slightly
reduced to its higher disk friction loss, specially in low specific speed pumps
where the impeller passageway is narrower. For this reason, a full center rib
design is to be used selectively.


Q - In impellers with staggered vanes, how are the vanes spaced apart? Are they
spaced equally, or at some angular distance based on other factors such as vane
number, or discharge angle?

A - The answer to this question is excluded in this article. Read more.



R: 1109- IMWI
C: design
F: impeller staggered


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Example of impeller with full
center rib and staggered vanes
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