Combination Air Vac Valve (CAV) Relocation

[Lan123]

Due to a potential conflict with a another utility provider I have to relocate an existing CAV and the vault. The CAV is at high point of a 16" ductile Iron water transmission pipeline. Can I relocate the CAV by installating a 16" "Tee" at the high point and then extending the branch of the tee horizontally for about 20' upto the proposed CAV location. Anyone has any prior experience with this type of an issue. Like to hear your experience.

Thanks.

 

[bimr]

The air release will not work unless you connect to the top side of the transmission main and have upward slope on the air release take off pipe all of the way to the air release valve.

You also run a risk of stagnant water in the dead leg created by remotely locating the combinatin air release valve. This stagnant water may be pulled back into the transmission main with vacuum.

Is it possible to eliminate the valve?

Have you considered moving the valve downstream? The air will be pushed down stream by the fluid. It may be acceptable if you install the valve at the location where the transmission line starts to slope downward.

 

[waterpipe]

Doing a vertical branching over the valve location is fine but I haven't seen the horizontal displacing.
20' is not a long displacement. Take a look to the pipeline gradient line and check whether it's a critical point or not (too close to gradient line, risk of major negative pressures). You should also try to re-place the valve so that it is being heat by the negative surge sooner than the main pipe.
Anyhow, If you provide a suitable slope toward your new location (let's say minimum 2.5% to be on the safe side) and try to get the connecting pipe with a diameter as close to the main pipe as possible, then it should be fine.
Please note the function during the negative pressure is more important. Under normal pressure, the trapped air would go forward to you detour branch and thus out of the main pipe.

 

[bimr]

Would have to disagree regarding the air bubbles moving forward. The air bubbles will not be carried downstream in the pipeline unless the velocity is greater than 3.5 to 4 ft/sec.

The air release is probably more important unless the vacuum release is installed to protect the pipe. Sometimes thin walled pipes are installed that can not withstand the maximum vacuum created by the water as it drops in elevation. Probably not a good design practice if that is the case.

Not that the outlet of the air release needs to be above grade and out of the vault.

 

[cvg]

horizontal displacement of 20 feet or more is very commonly done in urban transmission mains. Most cities do not want air release vaults or manholes located in the middle of busy streets which makes them extremely difficult to inspect or maintain. as a result, they are commonly tee'd and run to the side of the road, behind the curb and sidewalk. Regardless if this is the best installation method, it is generally done anyway. A tangential outlet is preferred over a standard tee and should be oriented at a slight upward slope as recommended previously.

 

[greggy]

In situations like this we tap the top of the main at the highpoint with a 1 inch corporation, then run a copper line to the location we wish and install a curb stop and copper riser in a valve box or meter box. This allows us to manually bleed the air off the main for operations and filling.

 

[Lan123]

OK folks. Thanks for providing me these comments. These comments will be extremely useful for me to decide on a feasible option.