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
T looks as if yo are using the GVF solver or WaterGEMS. The way to interpret these values is that the pipe will not be flowing full until you reach the bottom of the hill.
You may even want to make it a gravity sewer so that you can connect customers along the way.
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
If you have an air valve at the high point you will not have column separation. You will get air into the pipe which is different from column separation where the water vaporizes. Air and water vapor are very different.
The GVF solver for pressure pipes assumes the pipe will flow full. When you report negative pressure and you have an air valve, the interpretation is that the flow down the pipe is less that what it would take to fill the pipe.
Answer Verified By: Sayed Elhagr