PSV Cannot Supply Pressure and Caused ill-conditioning

I have a model setup that has a PRV and PSV in series. The PRV opens only if the pressure on side A of the system drops below 40 psi, otherwise it is closed. The model ran fine with the PRV. I then added a PSV to control the pressure on side B of the system. If the pressure dropped below 100 psi then the valve is to close. When I go to Analysis-> validate, no problems are found. However, when I run the model I get warnings saying PSV cannot supply pressure and PSV caused ill-conditioning. I am using this run to see how much fireflows will be increased on side A of the system, however, due to these warnings all fireflows are calculated at zero. Do you have any advice on how to troubleshoot this?

Thank you!

  • Hello Hannah,

    Try setting the status of the PSV to Inactive and compute the model. That would give you an idea of the pressure you are seeing around there to make certain that data you are entering makes sense for the system.

    You will also want to double-check other input in the model, just to be certain there is not a typo somewhere.

    Another thing that you can consider trying is making some adjustments to the calculations options. There are a new items that can be adjusted that can help with some valve operations. Please see the screenshot below for where these calculation options are.

    First, make sure that you are using "WaterGEMS 2.00.12" for the Engine Compatibility. If you are, the items in red above will all be available. You can try increasing the values for Convergence Check Frequency and Convergence Check Cut Off. For Convergence Check Frequency, try 5. For Convergence Check Cut Off, try 20.

    In addition, set the Damping Limit to 0.01. This assumes that the Accuracy is set at 0.001. You can find out more about what these different calculation properties do by highlighting it. Information on the property is available at the bottom of the dialog.

    If that doesn't help, please let us know. We will likely need to see a copy of the model. There are two options for sharing your model on Communities, whichever you choose please be sure to zip your files first. The first option is to attach the zip file containing your model to your reply on the forum using the Advanced Reply Editor (you'll find the link below and to the right of the reply box). If your data is confidential please use the instructions in the link below to send it via Bentley Sharefile. Files uploaded to Sharefile can only be viewed by Bentley employees. 

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    Regards,
    Scott
  • As Scott mentioned, the valves may be set up such that it is impossible to solve the network. Also, check the orientation of the valves. In some cases, a bypass pipe can be placed around the valves to help with convergence. We have a wiki article that explains this a bit more, which I just expanded to include a small example model:

    Ill-conditioning User Notification


    Regards,

    Jesse Dringoli

    Technical Support Manager, Haestad Products
    Bentley Communities Site Administrator
    Bentley Systems, Inc.

  • Hello Scott and Jesse.

    I wanted to write this comment 3 years ago, but forgot, and now while working on one model, searched again and found this post

    As a addition to your suggested process, I noticed that biggest problems is when PSV is controlling downstream demand nodes. To avoid that, while simulating big consumers for which I need to reduce flow due to pressure drops, most beneficiary method was to introduce a water tank, empty one, and add demand to that water tank. Tank needs to be dimensioned so that available flow is not filling it, rather used only for satisfying added demand. In this way, PSV works great with no ill-conditioning.

    Hope you can try this method and add it to Wiki as an option.

    TANK (base elevation as node elevation, maximum little bit higher and initial level is 0) --> add demand with demand curve to that water tank, the same one that was on demand node --> set PSV as you want