Impeller trimed and Flow increased 4

[MIANCH]

Hi,
We have trimed the impeller of a centrifugal pump and after triming the impeller this pump flow has increased and load has reduced.
I'm confused with this as I know by triming the impeller will reduce flow and reduce load on motor.
Could any one share his experience with me if have this type of problem.
thanks

 

[BigInch]

Since a good part of BEP efficiency is caused by matching incoming flowrate to impeller bite, if they were operating near BEP previously, but then trimmed the impeller, they may have managed to match bite more effectively and increased efficiency as well. Hard to say without the spec sheet and the operating logs to go along with it, but I don't have time for that anyway.

 

[Artisi]

A typical "my pump doesn't work, why not?" posting in which it is the pump at fault (as usual), nothing to do with the overall system, the operators, or changes made to the system,information which has to be squeezed out of the OP as if it were gold.
Guess it keeps us occupied and exercise the old brain.

 

[MIANCH]

Hi,
I got information on impeller triming,'ie' oreginal impeller dia meter was 366mm and 10mm is trimed.
Now the question is why manufacturers are not consulting with process engineers and validating the design parameters before for manufacturing the pump or any another equipments.
Thanks
MIANCH

 

[Artisi]

Seems someone is not listening, it now the manufacturer at fault.

 

[rmw]

Is there any kind of pressure regulator out there in the system downstream of the pump. Not a flow regulator, a pressure regulator. If there is a back pressure regulator that is throttling the pump to prevent overpressure downstream, its influence would be reduced upon trimming the pump impeller which resulted in a lower discharge head.

How about a by-pass or minimum flow regulator?

However, 10mm in 336 isn't a huge reduction.

rmw

 

[MIANCH]

Hi,
No presure regulator on this pump, this kero/ gas oil fractionator bottom pump for the bottom side pump. After triming the pump,the only change is control of FV increased around OP 2%.
Only apparent change is only FV out put and no other change.
Hope you will make some more assumption about this meyth.
Thanks
MIANCH

 

[ione]

Any info about total differential head?

 

[ccfowler]

Artisi,

It seems that we misunderstand everything. The pump manufacturers and others are expected to provide the proper pump and advice based on inadequate and misleading information. I'm sure that a variation of this philosophy is behind the attraction of VSD's to pretend to compensate for the effects of misinformation while providing assurance of optimal pump performance and dramatic energy savings (reality being both insignificant and unimportant).

Valuable advice from a professor many years ago: First, design for graceful failure. Everything we build will eventually fail, so we must strive to avoid injuries or secondary damage when that failure occurs. Only then can practicality and economics be properly considered.

 

[Artisi]

After 30 odd years in the pump business I have come to realise that;
1. it is nearly always the pump at fault.
2. if not the pump, then it's entirely the manufacturers fault.
3. there are no other causes which can affect pump performance as the pump should always fit the application perfectly.

 

[MIANCH]

ione,
There is no difference found in differential head.
Thanks
MIANCH

 

[Artisi]

MIANCH, it is about time you realised that it is unlikely the increased flow is the result of the impeller diameter change, the cause is external to the pump.

 

[ione]

1. Flow rate increased after impeller trimming
2. No change in total differential head
3. Brake horse power decreased.

BHP = Q*Ht*SG/(3960*pump efficiency)

The pump efficiency has changed, so the operating point is not on the same system curve as that it was before trimming

 

[MIANCH]

ione,
my pump head is 179m and differential head is 3.7m. Deisgn flow is 60m^3/hr and efficiency is 43%.
After triming why BHP increased and remaining power where is getting utilized.
Thanks
MIANCH

 

[QualityTime]

Why don't you plot the before and after pump curve so we can see what you are talking about. Put the numbers on a spreadsheet and draw where EXACTLY the pressure gauges are located with respect to the centerline of the pump and the pump nozzles.

1. Show us exactly how you did the head calculation in your spreadsheet
2. Is your flow meter calibrated
3. Are your pressure gauges calibrated
4. Send a picture of your installation showing the pressure gauges

What you are saying is occurring is impossible. To engineers, who understand pumps, you are not providing much information for anyone to comment on