Check valve for gravity hot water re-circulation

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by bhoth, Apr 25, 2016.

  1. bhoth

    bhoth New Member

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    Utah
    Hi All,

    I recently completed a dedicated gravity hot water re-circulation loop in my house. As part of the build I had installed a PVC non spring flapper check valve in the line. It was working perfectly. We went from 3-4 minutes hot water at the kitchen sink to less than 10 seconds.

    Then after a week or so I found out that I should not be using PVC in potable water lines. So I bought a brass flapper check valve at Home Depot and immediately started having cold water in my hot water line. It was most evident while taking a shower. By simply shutting off the loop (inline ball valve right before entering the bottom of the hot water heater) the hot water would return.

    My guess is the brass check valve is staying open and allowing water from the bottom of the hot water heater to be pulled into the hot water line.

    Please help me figure out a check valve that will work. Thank you!

    See pictures below:
    [​IMG]
    [​IMG]
    [​IMG]
     
  2. hj

    hj Master Plumber

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    What is the "horizontal' line that goes into that tee?
     
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  4. Widgit Maker

    Widgit Maker Member

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    Was it PVC or CPVC. You can use PVC on potable lines, you just cannot use on hot water lines. Its a heat thing.
    More likely that there is not enough pressure differential on the re-circulation to open the check valve so the circulation has stopped.

    I had the same problem. When I built my home many years ago I put in a re-circulation line with pump. After a couple years the pump quit. I took the pump out and reconnected the line until I could replace the pump. I found out that I had enough pressure differential that I didn't need the pump. That worked for many years (20) Then circulation stopped again. I concluded that it was the check valve. I have hard copper piping and the check valve was horizontal. I replaced the check valve but still didn't have circulation. I re-plumbed that section of pipe and set the check valve at about a 45 degree angle. Circulation returned. There just wasn't enough pressure to open the check valve.


    Suggest you try a CPVC ball check valve.
    ctubv-epdm.jpg
     
  5. bhoth

    bhoth New Member

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    The horizontal line is simply to bleed the line. It goes over to a floor drain nearby. I added it after realizing I had air in the line and this was my way of purging the air in the line.
     
    Last edited: Apr 25, 2016
  6. bhoth

    bhoth New Member

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    It was a PVC check valve.

    Is the CPVC ball check valve spring loaded? Everything I have read about using a check valve is do not use a spring loaded one.
     
  7. Widgit Maker

    Widgit Maker Member

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    Last edited: Apr 25, 2016
  8. Smooky

    Smooky In the Trades

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    The guy in the video has your same problem. He has a brass swing check but the swing disk is too heavy. He removes the heavy metal disk and creates a new plastic disk. He is better at moulding plastic than explaning the hot water heater.....He creates a mold and makes an exact replica. I think you could create a close match with thick plastic and a grinder.

     
    Last edited: Apr 25, 2016
  9. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    One guy suggested drilling a small hole in the moveable flapper seal. Enough for water to flow via gravity, but not enough to dilute the hot when slammed closed when drawing hot water.
     
  10. bhoth

    bhoth New Member

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  11. bhoth

    bhoth New Member

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    Actually it's the opposite, the recirculation line works great, but when some one is in the shower then it is pulling cold water from the bottom of the hot water heater. As I said in the first post, I have proven that by simply shutting off the recirculation line by the valve.
     
  12. Widgit Maker

    Widgit Maker Member

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    Then check valve must not be closing. Check direction of flow.

    OOPS, I see that it is correct. Perhaps it is defective and leaking slightly.
     
    Last edited: Apr 26, 2016
  13. Widgit Maker

    Widgit Maker Member

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  14. bhoth

    bhoth New Member

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    Ok I just ordered this 3/4 inch CPVC check valve. I hope it works as it was just under $40 with shipping.
     
  15. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Water will take the path of least resistance, and if the line from the bottom of the tank has less resistance than the normal hot, yes, you will need a check valve to prevent diluting the hot with the colder water from the bottom of the tank. Getting it to flow in a convection loop is one thing, keeping it from flowing backwards during hot water use is entirely different. One is pressurized, the other is not.
     
  16. bhoth

    bhoth New Member

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    Ok I have replaced the check valve with the CPVC check valve pictured above and it is doing the same thing again! It's pulling cold water from the bottom of the water heater. I can stop it by simply turning off the ball valve right before it enters the bottom of the water heater.

    I am really stumped at this point!
     
  17. bhoth

    bhoth New Member

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    The hot water heaters are Bradford White and it does look like there are heat traps on both the hot and cold side of both water heaters. (2 40 gallon connected in serial)
    Could this be the problem?
     
  18. Reach4

    Reach4 Well-Known Member

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    1. It would be a problem to have a heat trap on either hot, or cold on the second in series.
    2. It seems to me that two WHs in series would complicate analysis of things, and might confound gravity circulation, presuming they are both at about the same level.
    3. I would be surprised if the lower port on a WH delivered cold water. Less hot, sure. But if water is circulating, I would not expect cold water there.
     
  19. bhoth

    bhoth New Member

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    Can the heat traps on the WH be just unscrewed, or is it not that simple to remove them?
     
    Last edited: May 4, 2016
  20. Reach4

    Reach4 Well-Known Member

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    I have never done it. They differ, but usually I think it is just unscrewing with the right wrench. Your first photo may give enough info, but a closeup might help. Somebody will know I expect.

    http://www.bradfordwhite.com/heat-trap-fitting-vertical-or-horizontal-style seems to suggest that you might be able to remove a plastic cap and suck out the balls. http://www.bradfordwhite.com/important-announcments-18 seems to suggest that the pieces of the heat trap can be removed and/or replaced.

    See https://terrylove.com/forums/index.php?posts/449855/ post #28. You could also look through the first 27 posts on that thread, but #27 has the result.

    After thinking further, if removing the 3 heat traps (not the first cold one) does not do it, I would move the cold recirculation line to the second WH. Alternatively, just remove the hot heat trap on WH#2, and move the recirc line. That would seem to me to offer the best chance of success for your gravity system. I would not use a check valve unless it was something that was specially balanced to be normally open when there is no or little flow. No checkvalve would seem much easier to me, and maybe more effective.
     
    Last edited: May 4, 2016
  21. bhoth

    bhoth New Member

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    See a zoomed out view of both water heaters:
    [​IMG]
    See below a closeup: note the comment about the heat traps on both the hot and cold side

    [​IMG]
     
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