Plumbing – Do I really need this circuit vent if the sink vertical drain segment is 4′ away from the vertical dry vent

plumbing

Here is the layout and I am questioning the need to have the purple segment
the green blue selected segment is already in place, the green segment between the shower vent and the sink is what I am building (still dry fitting the pieces but I did not drill the holes for the studs to the left of the vertical green segment
As mentioned the distance between the two green verticals is 4'

I am also considering an air admittance valve
enter image description here

Update: Here is why I need to go down and not horizontal with the drain
enter image description here

Best Answer

If the slope of the drain is 1/4"-per-foot you can do without the pink vent. Be sure to measure your slope with a level. Don't just measure from the floor.

You don't need an AAV to delete the pink vent.

trap arm size    trap max developed length @ 1/4"-per-foot slope
1 1/4"           5 feet
1 1/2"           6 feet
2"               8 feet

Instead of the green branch drain having a vertical drop, just run it horizontally (with a 1/4"-per-foot slope) over to the corner. That is within the max length before siphoning could occur. edited CAD drawing with red line for branch drain

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