Pump impeller

[sujins]

Is there anybody know how much we can trim the diameter of impeller in percentage(Any limit to the original size)? And can we bring the affinity law to calculate the pump characteristic curve at reduce impeller size? Please suggust!

 

[sunloco]

In my mind I remembered normally the percentage is not more than 5% of original diameter of impeller ,otherwise the efficiency will drop down quicklly .

If you are allowed to trim the impeller ,you can calculate the characteristic curve according to affinity law

 

[checman]

sujins: It depends on the specific speed or type of the impeller. It is pump design specific so your OEM would need to tell you the recommended minimum impeller diameter for your pump. But in some general terms the radial vane impellers in your standard end suction pump are commonly cut approximately 30% If 10” is maximum diameter 7” may be the minimum. On a mixed flow impeller 20% is somewhere around the maximum cut. Again your OEM or the specific curve for your pump can tell you the minimum recommended diameter. Affinity laws work with the radial vane impellers and are more accurate with small changes in diameter where there should not be a big change in pump efficiencies

 

[JJPellin]

I would suggest caution using the affinity laws for more than about a 5% change in impeller diameter. If your required accuracy is not too fine, you can use the affinity laws much further. If it is a standard radial enclosed impeller, the efficiency of the trimmed impeller can be better if you only trim the vanes and leave the shrouds full diameter.

 

[Artisi]

You can put this in the useless information box - but for what it's worth, the minimum impeller trim is at the point where all the flow circulates withing the casing and nothing is discharged, up until this point you still have functioning pump unit.

The information you want is in the hands of the pump manufacturer, they can tell you what the minimum practical diameter is and what diameter to use for any specific duty, otherwise you have no accurate way of predicting other than using the affinity laws.

Naresuan University
Phitsanulok
Thailand