For the attached model, the start pump elevation is 75m, and the other end elevation of this model is 51M. And even compute the initial condition, there will be the message "Pressures below the lowest physically possible pressure in the system at one or more time steps".
If Start the Transient Solver, there will be the message "Initial pressure less than vapor pressure. At the pipe end(s), the elevation(s) or head(s) are incorrect." for nearly all of the pipes.
Have placed some Air valves in the model. So, what should we do to next to modify the model? Could you help to review the attached model and provide some suggestions on it?
Thanks a lot
Jinlong
This can be an issue when you are pumping downhill with an intermediate high point. When the pump turns off, the downhill section of the pipe will drain by gravity. In some cases with a steep slope the downhill section may never flow full.
You should first study the system and calibrate the model with WaterGEMS. Both WaterGEMS and HAMMER are based on full pipe flow. If the steady solution shows the HGL well below the pipe, you may not have full pipe flow. In that case a model like SewerGEMS which can model the draining and filling of the pipe may be more appropriate.
Is this drinking water, raw water or sewage? If it is drinking water, having negative pressure will violate most regulations. You may need to consider something like a pressure sustaining valve or place a storage tank at the high point..
Hi Jinlong,
You can find more information about this particle error here: User Notification "Initial pressure less than vapor pressure. At the pipe end(s), the elevation(s) or head(s) are incorrect"
I do not see any model attached to your forum post, or in our ShareFile system. Here is some information on how to share (zip the .WTG and .SQLITE files before uploading, or go to File > Save to Package): Sharing Hydraulic Model Files on the OpenFlows Forum
If the negative pressure issue occurs at a high point where an air valve would actually keep the pressure set to zero, you would indeed use the air valve as explained in this article: Modeling Air Valves At High Points in WaterCAD or WaterGEMS However, if this is in the context of a transient simulation, see the section "Transient Simulation Implications in HAMMER" in the aforementioned article - you may want to end the system at the high point location and replace the air valve with a Discharge to Atmosphere element.
If the negative pressure is occurring somewhere else, you may want to take a look at a few profile to see if there is a data entry issue, or perhaps the network is unbalanced.
If you need further help, please provide a copy of the model.
Regards,
Jesse DringoliTechnical Support Manager, OpenFlowsBentley Communities Site AdministratorBentley Systems, Inc.
Dear Tom Walski
Thanks for your kind instruction, and the model gets the balance after adding PSV components.
Best regards
Dear Jesse
Thanks for your kind instruction, your information is important for me to get to study the model and the model gets the balance after adding PSV components.