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Thread: Air Gap Overflows?

  1. #1
    DIY Junior Member RRGuy's Avatar
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    Default Air Gap Overflows?

    After months of intermittent stink in our new house, we finally discovered a untrapped, uncapped 1-1/2-inch drain in the ceiling above our mechanical room. (Behind drywall) It is a 2 x 10 joist bay. It was obviously intended as the discharge for the water softener. At the time we added the softener, the installer ran the discharge line up to the kitchen island and drained into a tapped fitting in the 2" PVC sink drain. (Illegal, I know)

    Now that we found the proper drain, I had a plumber install a trap and air gap for the softener. But when the softener backwashes, the air gap overflows and spills water all over the floor. Our first solution was to tie in roughly 18" of 2" PVC along with a 2" trap to create more space for the water volume/rush. Same problem. The air gap overflows. There is no room for a taller stand pipe because of the floor above.

    So now, we have the trap capped with a threaded fitting into the top of the cap. There is a check valve in line on the softener discharge.

    I know this is not ideal, but I don't have many options at this point. The entire basement is finished.

    Has anyone else come across this problem and what was the solution?

    Thanks.

  2. #2
    In the Trades Tom Sawyer's Avatar
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    Have the drain rodded out.
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

  3. #3
    Water systems designer, R&D ditttohead's Avatar
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    The drain should easily accomodate the flow from a standard softener. Even a large residential softener should not exceed 3-5 GPM flow. The most common drain flow rate is between 2.4 and 2.7 GPM. Have your drain line inspected for obstructions.

  4. #4
    DIY Junior Member RRGuy's Avatar
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    It's new construction and new PVC. There are no obstructions. It has proper fall. It runs about 15 ft and ties into a 3" main line that then ties into the 4" out of the house. The softener has a 2.7 GPM orifice on the backwash, but it still splashes out of the air gap due to lack of stand pipe height.

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    Water systems designer, R&D ditttohead's Avatar
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    Which air gap are you using? Depending on your water temperature, you could drop the DLFC button to 2.2 assuming the 2.7 is a clack button. The 2.2 will still give you approximately 4 gpm per sq. foot backwash rates. This is adequate for most standard softener resins assuming the water temperature is consistently cold. I dont have my charts near me now to give you the actual temperature/expansion... but this may reduce the flow enough to correct the problem. I am also assuming you have a 10" diameter mineral tank.

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    DIY Junior Member RRGuy's Avatar
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    Not sure which brand the plumber had on him. It was solvent welded to the PVC. It's not installed anymore... I've been looking online at some alternatives, but don't want to spend a bunch of energy swapping out different types only to get the same results.

    According to the softener company, if I reduce flow the resin won't flush/backflow properly. That was my first thought, to simply swap out the orifice. So that's out, unfortunately. Not sure what diameter tank I have, it's covered with a plastic sleeve that goes down to the floor.

    If you have any recommendations for air gaps that won't suffer the splash/overflow problems, I'd like to hear about them.

  7. #7
    Water systems designer, R&D ditttohead's Avatar
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    I have tried many. Most splash above 2.0 gpm. The "Gap-it" has a flow straightener, I have not tried that one yet but it makes sense if the water is coming straight off of a 90, the straightener should help. If you try it, let us know if it worked. I am really interested in this air gap but I rarely do installs anymore. It also has some nicely design splash guards. What is your water temperature? The backwash rate of the media is generically set at 2.7 for a 10" tank, but Fleck recommends 2.4 gpm. the manufacturers recommend approximately 5 gpm per sq. ft of bed area but this is dependent on water temperature. Lower temperature would require lower water flow rates. I have extensive charts detailing this but I wont be at my office for a few days to go over them and I do not recall the correct fomula for figuring it out. Basically, the flow rates recommended by the manufacturers assume a set water temperature. You will typically get nearly double the expansion of media from 40 degrees to 90 degrees water.

  8. #8
    That's all folks! Gary Slusser's Avatar
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    Disregard.
    Gary Slusser Retired (= out of business)
    Click Here to learn how to correctly size or program a water softener.
    CAUTION, as of Nov 12 2013 all YouTube videos showing how to rebuild a Clack valve have an error in them that can cause damage.

  9. #9
    In the Trades Tom Sawyer's Avatar
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    You need about 18" of stand pipe for the air gap to be effective and not splash. Without a picture I can only assume that the drain line is discharging into the bottom of the trap and without a stand pipe it is going to splash back some. Can the trap be lowered to accommodate a longer stand pipe
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

  10. #10
    That's all folks! Gary Slusser's Avatar
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    The 1.5" pipe is up in the ceiling in a 10" bay with the pipe horizontal or slightly downhill.

    There is no way to get any air gap to work on that pipe in less than 10" of vertical space.

    IMO following the pipe to where it goes vertical/down inside a wall is about the only choice.

    I do not like check valves in softener drain lines and having one will not provide for backflow protection or prevent cross contamination.

    If this were my house, I would have left the drain line alone and capped this 1.5" pipe when I found it. I wouldn't want a an air gap hidden in the ceiling or in a wall in my finished basement. But that's just me and yes I know that isn't to code.
    Gary Slusser Retired (= out of business)
    Click Here to learn how to correctly size or program a water softener.
    CAUTION, as of Nov 12 2013 all YouTube videos showing how to rebuild a Clack valve have an error in them that can cause damage.

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