I need help modeling a Hydropneumatic tank

[AB]

I have to add two tanks to this system and then develop the operation of each pump for each well using the hydro pneumatic tank(s). I don't fully understand what it is that I am trying to accomplish by doing this. That is, after I placed two tanks into the system, I'm not sure what the results mean, so its hard to try and change the design of the tanks for this system?? Does this make sense?? I am mainly looking for input about the tank design but any input about why something in the system is doing what it is would be greatly appreciated!! Thank You

I really struggle with interpreting the results. That is, its hard to find information as to why the system is doing what it is doing. For example, I have no idea why so many pumps shut off or how a node can have a pressure with no demand. These are things that kill me

[Mark Wilson]

Hi AB,

When you edit tank attributes, the levels (e.g. initial level) is measured from the bottom of the tank.  In other words, the elevation that you supply for the tank is usually the bottom of the tank.  Then min., max., and initial levels are measured up from that datum.  It looks like you have interpreted the levels to mean absolute elevation of water surface, thus you are getting very high head in your system and your pumps are not able to function pumping agains such high head.

Also, from the EPANET User Manual:

How do I model a pressurized pneumatic tank?

If the pressure variation in the tank is negligible, use a very short, very wide cylindrical tank whose elevation is set close to the pressure head rating of the tank.  Select the tank dimensions so that changes in volume produce only very small changes in water surface elevation.

If the pressure head developed in the tank ranges between H1 and H2, with corresponding volumes V1 and V2, then use a cylindrical tank whose cross-sectional area equals (V2-V1)/(H2-H1).

Mark

[AB]

Hi  Mark,

Thank you for replying to my post!! At this point I just want to acknowledge that I've read your reply and have taken your information to change some things in my simple system. Ill have a more thorough response in a few days!! Thanks again for taking the time to look at my file. I appreciate it!!

[AB]

Hi Mark,

So what you told me makes sense. What i was doing was setting the elevations in the tank to be total head and not hydraulic head. That is, I had the water surface elevation to be like 820 feet when what i really wanted was for the water surface elevation to be 20 ft. The tank that i need to model is open to atmosphere and uses an equivalent  HGL to mimic that of a pressurized tank, which i believe is the latter part of the EPANET User Manual section that you referenced. Thanks again!!

On Tuesday, October 20, 2015 at 7:43:15 AM UTC-7, Mark Wilson wrote: