Removal of Impeller

[behar]

In a two stage pump; if the head required can be adequately supplied by one impeller, which impeller should be removed?

 

[pmover]

my swag, the 2nd stage.

thoughts . . .

1) may have rotor imbalance/stability without 2nd stage impeller . . .

2) 1st stage may be design for low npsh - insufficient details provided.

3) you will likely be better off with pump suited for process conditions; than bastardizing existing pump.

frankly, i'd consult with OEM and obtain there opinion or expertise on the matter.

regardless, good luck!
-pmover

 

[sprintcar]

If your system equations equal one pump, then use one pump. Replace the 2nd one with piping and tag it for a spare.

"If A equals success, then the formula is: A = X + Y + Z, X is work. Y is play. Z is keep your mouth shut."
-- by Albert Einstein

 

[Artisi]

I would remove the second impeller, removing the first impeller means the inlet flow to the second impeller will have to travel thru the 1st stage volute discharge opening which leads to the second impeller inlet, this will have the effect of increasing inlet losses.

However, I would check with the manufacturer or agent for their advice on this.

Naresuan University
Phitsanulok
Thailand

 

[whizzz]

agree with artisi

 

[MikeHalloran]

I would slow the motor down some, and wait for demand to go back up.



Mike Halloran
Pembroke Pines, FL, USA

 

[bulkhandling]

An interesting topic.

When you remove either ist or 2nd stage, which curve do you follow? How do you know one stage is enough?

Or you may think to trim the impellers -- at least you have a curve to follow. -- or replace the pump with a single stage one.

 

[vanstoja]

You shouldn't remove either impeller stage if you can avoid it because you may be faced with difficult shaft radial or axial loading and rotordynamics rebalancing problems. The first stage is more important because it is usually designed to meet the cavitation design needs whereas the 2nd stage impeller may not provide features for cavitation control. If you are presently developing twice the needed head, then you are probably operating at a flowrate that is far below the best efficiency point (bep)flowrate but you need to know exactly how far below bep. If operating below manufacturer's recommended minimum flowrate, flow instability is likely to lead to high radial thrust loading and possibly excessive shaft vibrations. If you don't see excessive vibrations then you may be operating below the unstable flow range where continued operation without damage may be possible. Typically, worst instability flowrates are between 30 and 70% of bep flowrate.