Expansion Tank Question

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by steveg91, Feb 3, 2007.

  1. steveg91

    steveg91 New Member

    Messages:
    30
    I know, I know, so many exp tank threads and here a I am starting another one....
    Watts installation procedures say to drain the water heater before installing exp tank; the following from their instructions

    4.Shut off power source to the water heater, (electricity, gas, oil
    burner switch) and drain system following water heater manufacturer
    recommendations.
    5. Install the expansion tank in the system (refer to Figure 1).
    a. The weight of the expansion tank filled with water is supported
    by the system piping. Therefore, it is important that,
    where appropriate, the piping has suitable bracing (strapping,
    hanger, brackets).
    b. The expansion tank may be installed vertically (preferred
    method) or horizontally. Caution: The tank must be properly
    supported in horizontal applications.
    c. This expansion tank, as all expansion tanks, may eventually
    leak. Do not install without adequate drainage provisions.
    6. Turn on the water supply valve.
    7. Open a hot water fixture and allow water flow until all air is removed
    from the system.
    8. Reapply power to the water heater.
    9. Open a hot water fixture to allow a slight flow until the hot water
    has reached operating temperature.
    10. Recheck system pressure following Step 1.a through c.


    is this necessary, or do I just install it and go?????

    Thanks alot,
    Steve
  2. Cass

    Cass Plumber

    Messages:
    5,980
    Location:
    Ohio
    When it says to drain the system they don't mean the water heater. Their talking about relieving pressure and water in the lines.
    You don't need to drain the tank but I would check you water pressure first to be sure your PRV is working right and set the air pressure in the Exp. Tank 10# lower than the water pressure. That way the bladder in the tank is slightly inflated.
  3. Gary Swart

    Gary Swart In the Trades

    Messages:
    7,358
    Location:
    Yakima WA
    When I installed my expansion tank, I also installed a pressure gauge between the expansion tank and the PRV. It gives me a constant check on the pressure in my system. Might not have been necessary, but was cheap and easy to do.
  4. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,825
    Location:
    Cave Creek, Arizona
    instructions

    Instructions like that are written by someone who has never actually done the job, so sometimes they indulge in hyperbole to make sure they have covered all the bases. All you have to do is drain enough water out of the system to make your connection. As long as the pressure in the tank is below 150 psi, it will provide some overpressure protection, but it works best if the pressure is below your system pressure, (as long as it is not zero when the water is turned on. After the water is turned on, if the initial pressure is less than the system pressure, the air charge pressure will be the same as the water pressure.)
    Last edited: Feb 3, 2007
  5. harleysilo

    harleysilo New Member

    Messages:
    101
    Location:
    Georgia
    I thought draining the water tank also had to do with ensuring you got an accurate "unheated" pressure reading. When I recently installed mine I drained the water heater about 3/4 of the way, then turn the cold water supply back on untill water draining from heater was cold. Then filled it up and got my "cold water pressure reading".
  6. SteveW

    SteveW DIY Senior Member

    Messages:
    1,052
    Location:
    Omaha, NE

    I did that, too, and also put a ball valve between the gauge and the tank. That way, when the tank eventually fails, I can quickly isolate it until I can get a replacement.

    It's also kind of fun to isolate the tank right after using a large quantity of hot water, and watching the pressure gauge go up to 150 psi - open the ball valve, and instantly back to 60. Makes you a believer in the need for expansion tanks.
  7. harleysilo

    harleysilo New Member

    Messages:
    101
    Location:
    Georgia
    I hadn't thought of that, but when you have it set up you can periodically check to make sure your expansion tank stll works. That sounds like a good way to prove to an apprentice how it works, or a good classroom demonstration.....
  8. steveg91

    steveg91 New Member

    Messages:
    30
    Wow, Thanks so much:) I'm taking all these suggestions. Couple a things though,
    It seems like a good "standard" pressure setting is 60psi, is that so?
    also, let's say I do set pressure at 60, then what pressure should I set the expansion tank at??? I'm not sure what " a little lower" means, just want to do it right.:)
    My favorite plumbing supple has the Wat6ts PLT tanks not the DET, is this good enough:; also, at 60 psi with a 50 galloin tank Watts says to get the 2.1 gallon tank, some folks here say to get the 4 gallon one, some say 2.1, any more opinions on that????

    Thanks again,
    Steve
    Last edited: Feb 3, 2007
  9. Mikey

    Mikey Aspiring Old Fart, EE, computer & networking geek

    Messages:
    2,717
    Location:
    Central Florida
    Watts has a tank sizing calculator on their Web site. DET is recommended for potable water.

    I'm on a well, and supply pressure varies from 40 to 60 psi. Should I precharge to "slightly less" than 40 or 60?
  10. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,139
    Location:
    New England
    I'd personally charge it to the high point, in your case, 60#. That way, the bladder won't be flexing as much. Actually, with a bladder type pressure tank on a well system, I don't really see a need for an expansion tank for the water heater at all; you already have a huge expansion tank in the system - the water storage system. The small one normally used for a water heater and a PRV will functionally make your existing one seem a little bigger.
  11. Mikey

    Mikey Aspiring Old Fart, EE, computer & networking geek

    Messages:
    2,717
    Location:
    Central Florida
    Right, but when we leave the house for an extended period, we shut off the supply from the well, creating a closed system. We also turn power off to the WH, but the solar system continues to do its thing, so some expansion does occur. Also, eventually some municipality or other will require that we hook up to their system, and we'll probably need it then. Now is a convenient time to install it.
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