Pressure Control Valve in AFT Fathom

[Fooooks]

Hello Eng-Tips,

I am having some issues modeling what I need in AFT Fathom, but this questions can be asked without using the program as well.

We have a pump that needs to maintain a pressure drop of above 30 psi to work properly. (Leistritz L5NG Rotary Screw Pump). It is currently between 12" pipe.
To maintain this pressure drop across the pump, we were going to insert a pressure control valve on the discharge of the pump and control it's open percentage to control the discharge pressure of the pump. We have pressure transmitters on either side of the pump.

In AFT fathom, I am assuming an inlet pressure of 0 psig, which I modeled with an assigned pressure of 0 psig. Then I modeled a short length of 12" pipe. Then I modeled a Pump with a fixed volumetric flow rate of 1530 (max of the pump). Then I inserted a control valve after. Then another section of 12" pipe. And finally, an assigned pressure of 30 psig.

I set the control valve as a pressure sustaining valve for 30 psi. I also input it's % open and cv curve into the table. I am trying to run the program so that it tells me what % open I need the valve in order to maintain the 30 psi differential across the pump. When I run the program, the valve fails to the open position.

I created an excel sheet with the cv valve equation to get a rough estimate. It shows that in order to have a dP of 30 across the valve, the valve needs to be open between 20-30%.

Does anyone have some direction here?

If I need to provide more information or the file itself, please let me know.

 

[btrueblood]

"I modeled a Pump with a fixed volumetric flow rate of 1530 (max of the pump). Then I inserted a control valve after. Then another section of 12" pipe. And finally, an assigned pressure of 30 psig."

So, you fixed the outlet pressure at 30 psig, then asked what control valve setting would give 30 psig, and the code said "full open". Sounds about right.

Try running with no fixed outlet pressure condition.

Are you sure about the fixed volumetric flow condition (does the pump slip at all)?

 

[Fooooks]

It said it failed to fully open position, my mistake. I did not clarify. So I assumed it could not reach the 30 psi dP.

I was going to model different flow rates after I knew I had this simulation correct. If I do not run it with a fixed outlet pressure, what should I do? The program requires that the system have a beginning and end with no open end pipe.