IMPELLER CLEARANCES IN CENTRIFUGAL PUMPS

[kpandit1]

Dear All,

I want know about

1) what is clearance between impeller and back plate in non-metallic pumps
2) what is clearance between impeller and casing face in non-metallic pumps- axial
2) what is clearance between impeller and back plate in metallic pumps
4) what is clearance between impeller and casing face in metallic pumps- axial

how to adjust this clearances?

how does this affect pump performances??

 

[GPRnD]

Your best resource for a lot of those questions is to refer to the IOM of your pump supplier.

If you don't have a specific supplier you could refer to manufacturers who provide their IOMs for download. For example at the link below you can find IOMs for many different pump models. Most of these IOMs will state state design clearances in them as well as how to adjust if them.

http://www.gouldspumps.com/Tools-and-Resources/Literature/Posters/

How much they affect the pump performance depends on the impeller design and in particular the specific speed of the pump. Low specific speed pumps are much more sensitive to clearance (with some exceptions like barske impellers). Both efficiency and axial thrust can be affected. Hydraulic Institute standard 1.3 can probably give you some background on this. If you have a specific pump example and want to post the details here I can comment on the effect of clearances on that pump.

 

[HPost]

Any gaps between the impeller vanes and the housing will decrease the performance of the pump both in terms of head and volumetric efficiency.

Gaps of approximately 1mm - 2mm are most common and are usually a result of a trade off between performance and manufacturing cost.

The actual values you are after will depend on the fluid and its operating temperature as the material selected for the impeller and housing will have different CoLE figures and will expand at different rates, giving different clearances at different temperatures.