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.