Hi
I am modeling a sewer project and there is only one path for the Sewage Force-main. there is a high point in the middle of the path for direct pumping from Wet Well W-7 to Manhole Su-MH-1354 and there was a negative pressure at the high point , so I suggested to put pressure breaker tank Wet Well "W-20" , to overcome the negative pressures My Questions as follows:-
1- is there any other solution than using W-20 wet well ??
2- How to control the outlet flow from Wet well W-20 (2,915.5 m3/d) to be the same as pumped flow to the wet well W-20 (891.7 m3/d), I know that the outlet flow from wet well is based on static head and downstream forcemain size , but is there any way to control, because actually the flow which will enter to W-20 is 891.7 m3/d not 2,915.5 m3/d
Hydraulic model attached in below link
https://we.tl/t-uISz3GDFVr
Regards
Sayed Ali
Usually it is best to put an air release / Vacuum breaker valve at the high point. You don't want a tank full of sewage sitting at the high point.
Depending on the downhill slope after the peak you may end up with gravity (partly full) flow on the downhill side. How this shows up in the model depends on which solver you use.
If yo don't put a wet well at the high point, the second problem goes away.
Pressure breaker tank will not be filled with sewage and left for along time its volume will be just for 10 minutes storage ( For negative pressure break purpose only), so sewage water in shall be out instant, Moreover I already tried using vacuum valve, but it does not succussed because the negative pressure value is too high about - 7 bar as shown on the attached screen shot , also using gravity pipes after high point will results in manhole depths with 10 m approximately
I am using GVF Solver Sewergems?? What is the best solver to solve this negative Pressure , if there is a way to solve it
Regarding using gravity pipes , there is no residential buildings a long the path of this forcmain and gravity pipes will have deep manholes at some location 8 to 10 m depth.
There is no negative pressure. With the GVF solver, a negative value means that the pipe is not full.
In your case, the downhill pipe would empty when the pump turns off. When it comes back on, it would start to fill but wioudl never reach full pipe flow.
Sayed Elhagr,
You might find the information you are looking for in this Wiki article - Why do I get a negative pressure at a high point in my system? Shouldn't the pump add enough head to push the water over the hill?
Please let us know if it helps answer your question.
Thanks,Larry
I did not get what you mean by there is no negative pressure in GVF solver, can you explain this point more?
What I understand that when pump will start flow will reach the high point and then water column separation will happen and vacuum will happen at these high point and this the reason why we adding double acting air valve so when pipe line is filling accumulated air will be released and a water column separation will happen air will enter the pipeline to overcome vacuum condition
Larry
Thanks for your answer, my question that I provided one air valve and it does not solve the problem completely, so what is the solution rather tan converting the downstream pipe to gravity pipe
Thanks
Sayed
I suspect you are seeing the negative pressure in profile view and are concerned that is predicting column separation. As seen in this article, the negative pressure on the downstream side of an open air valve in profile view with the GVF-Convex solver can be interpreted as the part-full flow.
If by "solve the problem completely" you mean something else, please provide further screenshots and/or a copy of the model.
Regards,
Jesse DringoliTechnical Support Manager, OpenFlowsBentley Communities Site AdministratorBentley Systems, Inc.
Answer Verified By: Sayed Elhagr
Thanks Jesse, the article you mentioned explains the issue well
Many Thanks to all