Effect of impeller width on hydraulic of a pump

[NegNeg]

Hi all

I have a question...if we replace an existing impeller with a wider one, then the side gap between the impeller and the casing decreases (from w1 to w2, see the attached picture). what is the effect of this reduction in the gap size on the hydraulic of the pump?...assume that all the hydraulic of the impellers are the same, just the second one is wider.

 

[LittleInch]

An open impellor?

Any more information or drawings.

But looks to me like a larger impellor so it will impact the hydraulics.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[NegNeg]

The drawing is for a closed, double suction impeller.
However, I am asking generally...i.e., what is the the effect of gap on hydraulic of an open/semi-open or closed impeller...

 

[LittleInch]

Where is your wear ring?

I can only think there will be more flow, but we only have a bit of the picture (literally).

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Artisi]

Probably an increase in flow but governed by the impeller eye hydraulics with a change to NPSHr. Contacting the pump manufacturer is the only way to get the actual data as they can possibly get back to the original hydraulic design.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[Artisi]

LI, wear rings, probably radial will be on either side of the impeller (double suction) at the impeller eye/s.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[NegNeg]

thanks all
The picture is schematic and I do not have the full picture.
So if I understood correctly, less gap=higher Q = More efficiency due to less hydraulic loss...

 

[Artisi]

The gap has little to do with it, it's the width of the impeller vanes from the impeller eye to impeller discharge. Assume the change of width is not just at the impeller outlet but from eye to outlet.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[Artisi]

Not sure about higher efficiency, that would need testing to prove or disprove.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[Artisi]

What is the magnitude of increase you are looking for, there are a number of subtle changes can can increase performance.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[NegNeg]

Thanks Artisi
It is not a real or practical subject, just I was studying about it.
I was thinking if we decrease the gap, will it affect the recirculation flow in the zone between the impeller and the casing that in turn results in higher/lower discharge cavitation?

 

[Artisi]

The area between the impeller and case could be treated as a dead area and not contributing to the discharge flow, if there were "pump-out" vanes on the impeller shroud it could possibly result in some hydraulic effect, however I'm assuming there are no pump out vanes as there is no requirement for such.

I don't understand that you mean by discharge cavitation.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[NegNeg]

Maybe discharge cavitation is not a correct term.
I meant the formation of recirculation flow in the gap area and the effect of such a (strong?) flow on the impeller/casing surfaces.

Thanks for your explanations.

 

[Artisi]

It's all too airy fairy, as I mentioned earlier, you really need to get back to the original data to assertain the effect of changing the hydraulic design, ie. blade shape, width etc, this is quite a complex undertaking.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)