Air Release Valves - Drainage Force Main

[ar9]

I have a drainage pump station with vertical pumps and wanted your commentary on the placement of Air Release/Vacuum Valves. I have added a quick sketch to better illustrate the situation. Will the air release valve by the pump allow air in as flow goes through the drop? The discharge has variable conditions: 1) open discharge and 2) discharge when TW is at ~El. 7. I'm concerned about the head especially when the discharge end is open to atmosphere; will the FM be pressurized?. Any comments are greatly appreciated.

 

[bimr]

If you an air release valve, air will not re-enter. A combination air release/ vacuum valve will allow air to enter.

The pipe will have some backpressure because of the headloss cause by the high velocity.

You do not need the 2nd air release. Your velocity is relatively high at 10 ft/sec and the velocity will push the air out the end of the pipe.

 

[cvg]

with such a large pipe and steep 45 degree exiting section, it appears that your pipe may not flow full at the end

 

[chocobo1198]

bimr said you don't need the 2nd air release... but I'm not sure. If a vacuum develops in there, you might want a combo valve. This is especially true if you haven't designed your pipeline against a vacuum. Maybe bimr can expand further on the 10 ft/sec being sufficient to push air out so you can have better confidence.

If ultimately you decide to put a combo valve at the second location, I suggest sloping the pipe so you have a high point. This allows air to be trapped at the peak and that is where you would locate your air valve.

 

[bimr]

Pumping Station Design has an extensive discussion of the velocity to flush air bubbles out. With such a short pipe, there should not be any problem with flushing the air out.

See the attachment.

 

[chocobo1198]

Cool man. I'm only familiar with AWWA M51. I learned something haha.
Guess the only consideration left is a vacuum.

 

[ar9]

Thanks to all for the comments, all are very much appreciated.

I will have the first valve be an air release valve only, after all it is a high poiint. My concern was having a combination air release/vacuum, and it allowing air to entrain. For the second valve in the system, closer to the discharge, I will have a combination air release/vacuum valve, as I do need to have a vacuum break to avoid a siphon when pumps turn off, and TW level is high.

Does anyone have any comments/red flags to this setup?

Once again, thank you all!

 

[chocobo1198]

Only reasons I would want air to go back in is to prevent a vacuum collapse and to allow for drainage of a section of main. Your TWL at both ends are lower then the first hump so I think there would be a vacuum there when the pump shuts off. If you don't want air entrained, then just make sure your pipeline is designed to withstand external atmospheric pressure or whatever environment you're in. The last thing you want to see is your pipe collapsing/buckling because of air...