New GRAD - Impeller diameter

[abuzent]

I have a vertical turbine pump that will work 24/365 for 15 years, taking water from a river and pumping it to a processing plant.

Bidders for the pumps came back with impeller diameters above 90% of the maximum impeller diameter possible. One bidder claims that the impeller diameter in VTPs have much less room than in horizontal pumps and that it is typical to do have such tight clearances.

Is this true? if you have links that would be appreciated

thanks

 

[rmw]

I think you have mixed two topics in your question.

First thing you say is that they exceed 90% of maximum possible impeller diameter which is their right if you did not specify a specific limit on max. impeller diameters (which could then kick them into a larger frame size in order to meet your requirement for max diameter limitations.)

The impeller and bowl in VTP's are machined to close tolerances, much different to the tip clearances of a volute type pump so your vendor is correct in his statement about the impeller tip to bowl clearances.

If they were to offer maximum impeller diameter, the bowl would be machined out to a larger diameter, and the OD of the impeller would follow, but the clearances between the bowl and the impeller would be the same.

You are confusing how a volute type pump impeller functions within its pump housing and how a axial flow or mixed flow pump impeller works in it's housing which is the bowl.

The volute pump has close clearances at the pump suction (normally) which prevents recirculation in the pump. The only place to seal an axial or mixed flow pump is at the tips of the impeller blading.

rmw

 

[Artisi]

It would be nice to know what size pump unit you are talking about, this will allow for some meaningful discussion regarding your question, and secondly as pointed out by "rmw" what is the problem with an impeller diameter being greater than 90%?

Naresuan University
Phitsanulok
Thailand

 

[pumpkind]

I can answer what is the problem with impellers close to the maximum size allowed.
Particularly when it comes to new applications or extended plant life - the Process Guys are asking for some spare capacity on their pumps - usually 10 % more head available if necessary. Two issues here :
Firstly, this is mainly to allow for further pressure losses in the system as wear and tear appears or extra capacity if some other user require water ( cooling systems)
Secondly - the 10 % extra head (if needed ) will be delivered by fitting the existing pump with new impellers - obviously once cut to size the flow and head are fixed.