Pump operating above rated head? 1

[CrimsonEngineer]

I am selecting a submersible turbine well pump and am unsure of the definition of "rated head". The pump specifications say that the rated head is 179-ft. My design TDH is 207-ft. Based on the pump curve it looks like this is an efficient operating point for this pump. Is is advisable to operate a pump above the rated head? Is the rated head the maximum head that the manufacturer recommends?

 

[BigInch]

Depends on (1) if you can do it and (2)how you plan to do it (3) if you have the power to do it.

You're going to have to increase the rpm by about 8%, so you have to work out how you'll do that. (1) & (2) above.

In most cases centrifugal pumps can be operated at 8% higher rpm without too much difficulty, but that's not to say you might be able to do it without some shortening of MTBR.

If you're not at maximum impeller diameter for your pump, you might look into going to a larger diameter and keeping the same rpm.

Your discharge pressure will also go up 15%, so pay attention to any pipe pressure limitations there.

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"Pumping systems account for nearly 20% of the world’s energy used by electric motors and 25% to 50% of the total electrical energy usage in certain industrial facilities." - DOE statistic (Note: Make that 99.99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[Artisi]

Is this an existing installation, or are you making a new selection.

What specification are you talking about- Please explain the 179ft - is it?

1. an engineering spec. for the pump requirement / duty,
2. A spec. included with the pump curve / data.

Can you post a copy of the curve and the pump duty you require ie, flow and head, standing water tabe and draw-down in the well - how did you arrive at 207 TDH

At the moment don't really know what info' you have, what the operation is and pump capability to make any recommendations

 

[JJPellin]

I may have misunderstood, but I am reading this question differently. You seem to be asking if you can run the pump at a lower flow than rated. By stating that the head you wish to run seems to be an efficient operating point, I assume you mean you can achieve this head with the existing curve by operating at a lower flow. If the pump has a curve that is continuously rising to shut-off, the operating point at higher head will necessarily mean lower flow. This brings me back to your original question. The "rated" head of a pump is the head that the pump will produce at the "rated" flow. The rated flow is the flow which the purchaser specified as their flow requirement when they purchased the pump. The term "rated" is not usually used to define a fixed property of the pump. A centrifugal pump has a best-efficiency-point flow, a minimum stable continuous flow and an end-of-curve flow that are properties of the selected pump.

If I have interpreted the situation correctly, then you need to verify that the point where you want to operate is above the manufacturer's recommended minimum flow. And you have to have a control system that is capable or controlling the pump to that operating point. If, on the other hand, you want to achieve the higher head while still running at the rated flow, then BigInch has hit the nail on the head. You will need a larger impeller diameter or higher speed.

As Artisi noted, additional information would allow us to give you a more meaningful answer with fewer guesses and assumptions.


Johnny Pellin

 

[CrimsonEngineer]

Thanks everyone for your replies.

Johnny, I think you answered my question. I was just unsure of the significance of the "rated flow" provided by the manufacturer. Based soley on the pump curve this pump will work for me. I will be slightly to the left of the best efficiency point and will be producing less than the "rated flow" at more than the "rated head". At this point I am still at a pump eff=76%.

This is a Grundfos pump and the rated flow and rated head are given in the technical specifications. I started to question the selection because using Grundfos webcaps catalog and selecting my design operating point under the advanced selection graph, Grundfos eliminated this pump.

I will give Grundfos a call to be sure but thanks for the advice.

 

[Artisi]

Giving the lastest info in your original post would more than likely have given you an answer with the first reply from BigInch.

 

[BigInch]

I'll give Pellin the well deserved credit. It really didn't occur to me that someone might be asking about running 10% higher than rated head while STILL ON THE SAME FREEKING CURVE!

**********************
"Pumping systems account for nearly 20% of the world’s energy used by electric motors and 25% to 50% of the total electrical energy usage in certain industrial facilities." - DOE statistic (Note: Make that 99.99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[Artisi]

Maybe Johnny's crystal ball is better than our's and yes, a good call on his part.