Water Heater Expansion Tank Revisited

Discussion in 'Plumbing Forum, Professional & DIY Advice, Tips & ' started by themp, Jan 22, 2011.

  1. themp

    themp New Member

    Messages:
    73
    Location:
    NC
    So, decided to install an expansion tank today and it completely removes the pressure spike I was having and the release of this pressure through the toilet around 80 PSI. So you could say I am a fan at this point, but you will have to maintain it. It said it was pre-charged to 20 PSI but it really was 15 PSI, could be it was cold. But in any event this is like keeping your tires inflated to the correct pressure.

    Now the most interesting thing that happened in all this expansion tank discussion is that I visited my son over Christmas and his new house. It is over ten years old and when I went into the garage where the gas water heater was I noticed right away that his TP valve was dripping. He had a bucket under it. He said it only drips a little. Any way we took the time to replace this and in the process decided to survey his whole house plumbing for expansion tank and pressure reducing valve. What we found and this house was inspected when he bought it was:

    1.) No pressure reducing valve as the previous owner had removed it. You can see where it was hanging near the expansion tank. The house pressure is 90 PSI.
    2.) The expansion tank is toast, totally filled with water.
    3.) The water heater is plumbed backwards the hot water is exiting the cold side of the water heater and a shut off valve is on the hot side not cold. Someone had painted on the ceiling where the copper pipes enter a red ring around the hot side. The water heater does seem to work correctly so the plumber must have switch the drip tube.

    My son was not into going into any expense as this point and since the pressure reducing valve was removed he does not have a closed system, so the expansion tank is useless anyway. So, he decided to think about it.

    So, he has 90 PSI open system, house is plumbed with some kind of white translucent plastic pipe. I never thought of looking at what it was.
  2. Terry

    Terry Administrator Staff Member

    Messages:
    14,776
    Location:
    Bothell, Washington
    Not closed? If there is a check valve on the water meter, it could be.
    Call them and ask. In many areas, they are changing out old meters for those with check valves, creating closed systems problems with expansion.
    I know that much of Redmond and Sammamish are like that.
    Pressure Reducing valves sometimes need repair (rebuild) or replacement after ten years.
  3. shacko

    shacko Master Plumber-Gas Fitter

    Messages:
    561
    Location:
    Rosedale, Md
    You should not be running anything over 80 lbs without a PRV and an expansion tank, CODE plus it keeps wear and tear down on your system (normal system in a house is 60-65lb.).

    >>>So you could say I am a fan at this point, but you will have to maintain it. It said it was pre-charged to 20 PSI but it really was 15 PSI, could be it was cold. But in any event this is like keeping your tires inflated to the correct pressure<<<

    Expansion tank need to be set to the INCOMMING WATER PRESSURE with the water disconnected from the tank. :confused:
  4. Gary Swart

    Gary Swart In the Trades

    Messages:
    7,308
    Location:
    Yakima WA
    80 psi may be code, but it is way higher than necessary. I set my PRV and expansion tank to 50 psi and it is just fine. When I first installed the PRV, I knew nothing about expansion tanks, but I soon learned! My T/P began to discharge, so off to Ace Hardware and a new T/P cause I'm no fool. Yeah, right. New T/P discharged just like the old one. So not to be bluffed into anything, I go yet another T/P, and, you guessed it, same problem. That's when I learned about expansion tanks. So off to L***s. The "expert" there thought I needed a pressure tank for a well! He'd never heard of a thermal expansion tank even though they sell PRVs. Stopped at HD and found what I needed. End of problems. I did branch off for a couple of hose bibs before the PRV and plumbed those lines with 3/4"; mucho flow and pressure on those lines.
  5. themp

    themp New Member

    Messages:
    73
    Location:
    NC
    Yes I added pressure to the expansion tank to equal what my pressure reducing valve is set at(45 PSI). Been watching my pressure gauge with max setting all day and it has not moved. :)
  6. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,814
    Location:
    New England
    For those that don't believe...this is exactly what it is designed for, and it does the job as designed. Those that say 'I've got a bypass on my PRV and don't need one' are totally missing the point - the bypass only works when the internal pressure IS HIGHER than the supply, so each time the WH runs without an expansion tank, the pressure will spike until it reaches the supply...not why you installed the PRV in the first place.
  7. ballvalve

    ballvalve General Engineering Contractor

    Messages:
    3,261
    Location:
    northfork, california
    Sounds like a call for the disbeliever...

    http://www.cashacme.com/_images/pdf_downloads/products/expansion_tanks/te_series/TE_Spec.pdf

    Even with an expansion tank, the pressure may rise to 150 psi, it just takes more time. Since the tanks are rated for 150 PSI thats a mighty fine line, and likely why so many of them are silently broken.

    Even without any overpressure, they are absolutely going to bust in 3 to 7 years. Quietly, no signal, no notification. Now you are back to the system pumping up to 150 psi.

    A relief valve at 125 PSI sure sounds like cheap middle line insurance to me. It also announces that your Expansion tank is toast.

    1/2" aqua pex is rated for 130 PSI at 120 degrees. I sure don't want to test that figure when I have thousands of feet of it in the slab. As many others.

    So the mid range relief valve saves your pex from a catastrophe, and tells you to check the ex. tank.

    How can one debate the advantages of that?

    http://www.grainger.com/Grainger/US-GAUGE-Pressure-Gauge-1X808

    Here is a nice gauge to put on the water heater outlet. Others are available with higher PSI range. This will tell you if your water heater is working right and check on the ex. tank quite nicely.
    Last edited: Jan 23, 2011
  8. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    A simple relief valve set at 125 may discharge some water several times a day as the water heater runs. Are you OK with that? With a properly sized expansion tank, you will NEVER see thermal expansion anywhere near 150 PSI. It takes very little volume to absorb the volume increase caused by thermal expansion.
  9. themp

    themp New Member

    Messages:
    73
    Location:
    NC
    The sad thing is that in my city it is required to have a pressure reducing valve and expansion tank. Most homeowners never know when the pressure reducing valve or expansion tank fails, unless it trips the TP valve and they call a plumber. They just comment and say that they like the high water pressure. These devices are usually buried in the crawl space also and no one ever goes and looks at them.

    You would think someone would have invented an expansion tank that does does not use a bladder. Spring/piston type arrangement, just like hammer arrestors. My 45 PSI has been solid for over a day and half now, so the expansion tank does work well and I am a convert, but it now has to be monitored. Since my tires lose air pressure over time, I assume the expansion tank is going to do the same. And also my fear is that bicycle valve starts failing from continual testing.
  10. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,263
    Location:
    Cave Creek, Arizona
    The bicycle valve will not fail from continual testing, but you WILL eventually drain the air out if you lose a little bit every time you test it.
  11. Terry

    Terry Administrator Staff Member

    Messages:
    14,776
    Location:
    Bothell, Washington
    Gee, I wonder when I have changed my schrader valves on my cars and trucks?

    Attached Files:

  12. ballvalve

    ballvalve General Engineering Contractor

    Messages:
    3,261
    Location:
    northfork, california
    I'm suggesting the expansion take the rise in water volume, and it will, if properly sized, and there will be NO pressure increase noted.

    Thus if you see water at the 125 psi relief valve you just learned your tank is shot. You will not have any water drip on a daily basis.

    Now you have time to get a new tank before the 125 +/- relief valve fails and you move up to the 150 PSI job.

    If the ex tank mfgr's added a miniature relief valve to alert us of its failure, you would have all that in one package.
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