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  1. #1
    Join Date
    Apr 2009
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    Default how to drain an expansion tank that has no flow in valve?

    Hi,

    I have an old water boiler and a 15gal expansion tank. The boiler is Kenmore Boiler Sears Model (22996156). No manufacture info for the tank.

    After some study on how expansion tank works, I started to think how to either check for water clogging or just drain this tank. I then noticed that there is only one hand valve for draining out of water, but no valve to control the flow between the boiler and the tank! And there is no way to look inside the tank -- a steel tank.

    so does this means that if I want to drain this tank, i have to drain the whole system?

    thanks!

  2. #2
    Join Date
    Feb 2008
    Posts
    555

    Default Re: how to drain an expansion tank that has no flow in valve?

    I would recommend either installing an isolation ball valve ($5) between the boiler and expansion tank, or installing a modern bladder-type pressurized Extrol #30 expansion tank($35), & just leave the old steel tank where it is between the floor joists.

    The Extrols come pre-charged at 12 psi, which is nominal for nearly all boilers.

    This would entail draining the system, but the fix would be permanent & avoid future troubles.

    Many of these old boiler systems were originally OPEN systems that didn't have an isolation valve & the expansion tank openly vented to the roof or to a basement sink.
    Last edited by NashuaTech; 09-23-2009 at 08:50 PM.

  3. #3
    Join Date
    Apr 2009
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    2

    Default Re: how to drain an expansion tank that has no flow in valve?

    Here are the pictures:

    The first one is the whole view and the 2nd one is the inlet part of the tank.


    And i am also showing the boiler display. After turn on the water, the pounds meter slowly increases and now it is reaching 45 pounds. I leave the valve on to see how far it will go. just want to know if this is normal?

    http://s558.photobucket.com/albums/ss25/lyrebird_bbs/

  4. #4
    Join Date
    Feb 2008
    Posts
    555

    Default Re: how to drain an expansion tank that has no flow in valve?

    Having trouble trying to get your Photobucket photos to load on my system.

    No, pressure that high is NOT normal---there are 2 safety devices on all boilers that are designed to keep the pounds pressure (psi) below 30 psi, and under normal conditions under 20 psi in most cases.

    One of the safety devices is the EXPANSION TANK, which is always half filled with air---this acts as a cushion for the expanding water when it heats up inside the system (water expands approx. 5% when it is heated)---this EXPANDED VOLUME will burst something in the system if it is not compensated for.

    The primary safey device for the expanded water is the PRESSURE RELIEF VALVE that sits on top of the boiler.

    The PRV has a calibrated spring inside that will open when the expanded water pressure reaches 30 psi or higher, thus protecting the boiler and associated pipes from damage.

    Sometimes the WATER INLET VALVE which drops the water pressure from the "house value" of 50 psi to the 12 psi that the boiler uses, goes bad & allows too much pressure into the boiler system.

    DO NOT USE THE BOILER until you have determined why 40 psi is entering the system---turn off the water inlet valve so that no additional water can enter the boiler until you determine what the problem is.

    If you can find the PRV, press the little handle to relieve the pressure down to below 30 psi---the PRV usually has a long drain tube from the top of the boiler down to the floor to direct the discharge water to floor level.

    To view a photo of a typical pressure relief valve, click onto the site below, then onto "water safety & flow control", then onto "Relief Valves", then onto "Pressure only relief valves", then onto "374A".

    As noted, the valve has a right angle copper tube attached going down to the floor to direct the water down.


    http://www.watts.com
    Last edited by NashuaTech; 09-25-2009 at 09:15 AM.

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