Equal water rating in stock pumps

[rkuhn]

Hi,

In a stock pump manufacturers'curve two capacities and corresponding TDH are indicated: The rated one for stock (5675 USGPM @ 73.5ft)and the "equal water rating" (5900 GPM @77 ft).
The fluid is unbleached kraft with 3.5% consistency.

Nevertheless, from Gould pumps' "centrifugal pump fundamentals" web site I got: "Recent testing on various types of stock has indicated that pump performance is the same as on water for stock consistencies up to 6% O.D. In other words, water curves can be used to select stock pumps, as the capacity, head and efficiency are the same as for water."

I would like to obtain the "real" or stock capacity from the water-based curve, for another operational point.

Cheers and thanks for you help,

 

[TenPenny]

In the old days, people used TAPPI-approved correction factors for pumping stock. However, for a long time (20 years +), no factors are used under 6%, because testing has shown that at those consistencies, stock performs the same as water (assuming air entrainment is not an issue) from a pumping point of view.

I'm curious about what year that corrected curve is from, and what air entrainment is there, and a bunch more info about your application. I haven't seen a curve on standard stock corrected for many, many years.

I will do some digging tomorrow when I'm in the office, to see what I can find.

 

[Artisi]

Correct, it has been known for something like 20 years that upto and possibly slightly above 6% paper stock has a friction loss equal to or even below that of water friction loss. Air-entrainment of course is another problem and one of the main factors in poor pump performance when pumping paper stock.

Unfortunatley I don't have the data anymore but I think it is available on the "net" and possibly in the ITT Goulds site.

 

[rkuhn]

Hi,

Thanks TenPenny and Artisi for your help. The curve's issue date is June/89. This pump service is blending tank feed from a Hi-density storage tank. Air-entrainment can be an issue here, but I have no data about this.
I've made some measurements (head, flow and input power) and got an operating point close to the performance curve and to the left of the original design point (due to a lower flow demand).

I'm evaluating to replace the throttle valve control by a VSD drive.

Cheers,

 

[Artisi]

As you are pumping from a blending tank there is a possibility what you could have entrained air in the pumped stock.
But for 3.5% unbleached kraft I would only considser this as a straight water duty.However, you haven't indicated that you actually have a pumping problem, if you have,post more detail and will see if we can help.

 

[TenPenny]

So, it's 3.5% stock, but fed from a high D tower??

Does that mean you've got dilution between the tower and the pump suction? These applications are, as you note, subject to nasty amounts of air. I would have expected the high d tower to be in the 10% range, and that can have a nasty amount of air.