Expansion tank question

Discussion in 'Plumbing Forum, Professional & DIY Advice, Tips & ' started by drvnwell, Oct 29, 2013.

  1. drvnwell

    drvnwell New Member

    Messages:
    8
    Location:
    Albuquerque, NM
    The drain valve from my water heater keeps draining. I replaced the relief valve but that did not remedy the problem. I tapped the expansion tank and it appears to be full of water. It is a watts DET 12 M1 which is no longer produced. What is a good compatible replacement? Any suggestions would be appreciated.
  2. Sean Beck

    Sean Beck Plumber

    Messages:
    68
    Location:
    Toronto, Ontario, Canada
    If the drain valve was leaking, and not the T&P relief valve then would this not be an issue with the actual drain valve. If the expansion tank was water logged and there was no room for expansion, then the first place it would drain should be the relief valve, not the drain valve.
  3. drvnwell

    drvnwell New Member

    Messages:
    8
    Location:
    Albuquerque, NM
    I misspoke, it was the T&P relief valve, sorry.
  4. Gary Swart

    Gary Swart In the Trades

    Messages:
    7,351
    Location:
    Yakima WA
    If the expansion tank is full of water, it is shot and needs to be replaced.
  5. Terry

    Terry Administrator Staff Member

    Messages:
    15,048
    Location:
    Bothell, Washington
    First throw a pressure gauge on the system and find out what your water pressure is.

    If it's over 80 PSI, you need to either fix a PRV Pressure Reducing Valve, or add one.
    I use a 2.1 gallon expansion tank on a 50 gallon water heater.
  6. jm66208

    jm66208 Member

    Messages:
    99
    Location:
    KC
    Remove the valve cap off the schrader valve on the bottom of the tank & press on the valve stem. If water bubbles out, the tank is shot. Seems like every watts tank I check is bad.

    valve.png
  7. Caduceus

    Caduceus Master Plumber

    Messages:
    136
    Location:
    Pittsburgh, PA
    The Watts det 12 is a 4.5 gallon thermal expansion tank. Thermal expansion tanks (TETs) are determined by the size of your water heater, but buying a TET the same size as the bad one should match up. Be sure the tank is for 'Potable Water'. Remember to get a gauge at the store to screw onto a hose connection and check your house water pressure before installing the TET. You will notice there is a thread protector on the connection to the water system and a smaller cap on the schrader valve for pressurizing the TET. You can use a bike pump, but I recommend using a compressor or going to a gas station to pressurize the tank to match the house water pressure. Leave the thread protector on the 3/4" water connection side until you are ready to install the TET to keep from damaging the threads.
    If your water pressure is higher than the precharged pressure and you do not add pressure to the TET to match it, your TET bladder will be destroyed and useless in a matter of weeks or months and you'll be back to square one again.
    Last edited: Oct 29, 2013
  8. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,684
    Location:
    Cave Creek, Arizona
    quote; If your water pressure is higher than the precharged pressure and you do not add pressure to the TET to match it, your TET bladder will be destroyed and useless in a matter of weeks or months and you'll be back to square one again.

    That is hyperbole. All that will happen is that the tank will be slightly less efficient, but not to the extent that anyone would ever know the difference. IF the pressure is higher than the water system pressure, then the tank may NEVER work, but again no one might notice it.
  9. Caduceus

    Caduceus Master Plumber

    Messages:
    136
    Location:
    Pittsburgh, PA
    No, it is not hyperbole. What I'm saying is this, hj; If your house pressure is 60 psi and the precharge pressure is 20 or 40 psi you will be extending the bladder by 40 or 20 psi, respectively, and the acceptance volume that the expansion tank was designed to handle will no longer accommodate the size of the water heater.
    This is why plumbers and DIYers who assume the tank is precharged and needs no adjustment will install them and the TET goes bad shortly afterwards. It is part of the warranty and installation guidelines from the manufacturers.
    I guess I need to explain that if the existing water pressure is less than the precharge of the TET, then you would simply let some pressure out of the tank so that they match up and check it with a tire pressure gauge.
    Now I have a some questions for you, hj. Why would you make a completely unnecessary comment that I'm being dramatic and that the recommendation that I made is not needed when what I have described has been common knowledge among plumbers for years and can be easily confirmed by all manufacturers and other plumbers? Why? Is it a common theme in Terry Love's forum to contradict other plumbers who actually have good advice or make simple comments and additions to posts? Is it? And as a moderator are you an example of what else to expect from this forum? I respected your insight over the past few years even though we haven't always seen eye to eye, but by calling my sound advice 'hyperbole' is very insulting.
  10. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,053
    Location:
    New England
    FWIW, at least from what I've seen, there is little moderation on this site in comparison to many others out there. This has good and bad points. Maybe there's a lot more going on behind the scenes, but I'm here often enough to likely notice if something has been tweaked or is now missing. I see no discernible pattern of that happening.
  11. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,684
    Location:
    Cave Creek, Arizona
    There can be a wide margin between "good practice" and "usable". The precharge SHOULD be at or below the system pressure, but it it is not, the system will compress it to the proper point. it is when it is too high and the air cannot adjust itself to the system pressure that it only works when the pressure rises above that level that it becomes a problem. When the tank is "empty" the bellows is all the way against the "inlet opening". When it is full, but no pressure, it against the Shraeder valve end. Between those two points the bellows folds to accomodate the volume differences. If it were under ANY stress it would be either when it is empty or no pressure, not under any other condition. But I would not be dogmatic and tell the customer to check the pressure every month to make sure it is proper, because he could not do it unless the system was drained. When the system is pressurized the air pressure will ALWAYS be at the system pressure.
    Last edited: Oct 30, 2013
  12. Caduceus

    Caduceus Master Plumber

    Messages:
    136
    Location:
    Pittsburgh, PA
    I never suggested checking the pressure every month. I also understand that the system must be drained to accurately test the TET's pressure. Symptoms and actions of the water system will let you know when there is a thermal expansion issue. But again, somebody on this forum has tried to explain away the simple and practiced advice that I gave when there is nothing wrong or faulted with it. My experience as well as the application of items dictated by the manufacturers have proved that by not following the basic installation methods will cause premature failure of the product. Explaining to me what I already know doesn't change that what I said to the OP was absolutely correct and didn't need any negative or devaluing comments. It's as if you didn't answer my question but just talked in a circle around it while still trying to sound justified.
    This has happened on the posts that I've made regarding vacuum relief valves on hot water tanks and another thread where I recommended not turning down/off water heaters for days so that bacteria and legionella are not an issue when returning home after days away.
    On those threads, as well as this one, somebody jumps into make it sound like I'm giving inaccurate or hack advice when in fact it is part of the basics that licensed plumbers practice when in somebody's home.
    I'm sure you can find the threads from my profile, if you are interested, but doubt that many members here would be willing to say "oops, I was wrong, sorry..."
    It would be explained away again that I must be too sensitive or speaking in hyperbole.
    It's starting to remind me of some egos in the PZ.
  13. Tom Sawyer

    Tom Sawyer In the Trades

    Messages:
    3,184
    Location:
    Maine
    Ah yes, PZ a veritable wasteland of useless advice and pointless argument. If everyone would just open that little piece of paper or the manual that comes with the equipment and then actually read it, far more products would last far longer than they do. 90 plus percent of all returned equipment is due to installation error.
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