Decreasing Pumping Flow Rate
Decreasing Pumping Flow Rate
(OP)
Hello,
I am working on the application of an air operated Pacer centrifugal pump for a pumping application. I believe the flow rates we will get using it in our system will be too high. Would the best way to decrease flow rate is to add a Pressure Reducing Valve on the discharge side? Any other methods? Is the PRV is correct sizing would be:
1. Calculate discharge head without PRV.
2. Calculate difference of discharge head needed for the correct flow rate on the curve minus the rate you will get in your system.
3. Find K needed to get pressure drop as high as on the pump curve.
3. Calculate Cv for the pressure reducing valve using Crane manual.
Any other thoughts? Orfice in pipe? Throatting discharge gate valve?
Thanks
I am working on the application of an air operated Pacer centrifugal pump for a pumping application. I believe the flow rates we will get using it in our system will be too high. Would the best way to decrease flow rate is to add a Pressure Reducing Valve on the discharge side? Any other methods? Is the PRV is correct sizing would be:
1. Calculate discharge head without PRV.
2. Calculate difference of discharge head needed for the correct flow rate on the curve minus the rate you will get in your system.
3. Find K needed to get pressure drop as high as on the pump curve.
3. Calculate Cv for the pressure reducing valve using Crane manual.
Any other thoughts? Orfice in pipe? Throatting discharge gate valve?
Thanks





RE: Decreasing Pumping Flow Rate
RE: Decreasing Pumping Flow Rate
It would therefore make some sense to run the pneumatic motor from a pressure regulator to slow it down and move the pump curve in toward the origin. They don't give curves for speeds other than 3450 and 2900 rpm, so you'll have to use affinity laws to estimate what the liquid discharge pressure will be at your desired operating point.
I suppose you could get closed- loop control by running the air motor from a pneumatic relay controlled by the liquid discharge pressure.
Mike Halloran
Pembroke Pines, FL, USA
RE: Decreasing Pumping Flow Rate
Naresuan University
Phitsanulok
Thailand
RE: Decreasing Pumping Flow Rate
From my initial calculations (don't have piping layout yet). I would say that the flow would have to be reduced from 50 GPM to around 10 GPM. Curve speed is at 3450 RPM so I would decrease the speed to around 690 RPM (using Affinity Laws. Don't know if that is possible just by turning down the PSI of air I deliver to it. Looks like it might be possible. Any thoughts?
Looks like the motor curve is horsepower vs. speed with different lines for different PSI of air. Is this horsepower BHP or WHP??
Thanks.
RE: Decreasing Pumping Flow Rate
RE: Decreasing Pumping Flow Rate
Mike Halloran
Pembroke Pines, FL, USA
RE: Decreasing Pumping Flow Rate
Throttling the discharge valve may be the simplest option, but this can be expensive with pneumatic prime movers.
The procedure you mentioned above using a pessure reducing valve works fine but speed control is better.
RE: Decreasing Pumping Flow Rate
Rather than throttling flow or altering impellor, I suggest adding a recycle loop. Makes it easy to fine-tune desired flow, and can easily get more if conditions change.
Ken