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Thread: expansion tank and TP valve questions

  1. #16
    Plumber jimbo's Avatar
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    Quote Originally Posted by ballvalve View Post
    I really don't get the 150 psi rating on the T&P valves. By that time, the old toilet supply hose blew and ruined your wood floor.

    I like Watts pressure relief valve made just for water heaters, as backup to the stupid t&p's and exp. tanks that blow silently and plug your fixtures with gunk.

    http://www.watts.com/pages/_products...ls.asp?pid=564
    The 150 PSI rating is to protect the water heater from pressure higher than that point, which can damage the tank. You MUST have "T & P" because you must also protect against the T.

    All components in your plumbing system, including the toilet and its supply lines, are designed for a test pressure of 150 PSI. The normal operating pressure should not exceed 80 PSI, and your house should be built so that is does not ( PRV installed if necessary). There is no code requirment to PROTECT your house should the pressure go higher. The expansion tank will help to keep the pressure much lower than that 150 PSI number.
    A bypass on a PRV will only keep the house pressure from exceeding the street pressure. That is of little comfort is the street is well above 100, maybe above 150.

    I don't understand about the silent blowing and the gunk???????

  2. #17
    General Engineering Contractor ballvalve's Avatar
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    Silent blowing: Expansion tanks do not give any indication when the bladder breaks. And that is a certainty, if anyone works on well bladder tanks, in about 3 to 7 years.

    Gunk: the air half of most tanks is raw steel, and condensation causes bacteria and rust to grow. When the bladder silently ruptures because the air charge was lost
    [all tanks lose air on a predictable basis and are rarely maintained] this soup ends up slowly in the water supply.

    Much of PEX does not meet the 150 psi rating at certain temperatures, therefore I propose a pressure reducer valve set around 50 psi, then the ex. tank which will handle spikes if properly sized, then a relief valve set at perhaps 125 psi to protect the ex. tank from higher pressures and to save your pex and to alert you of the failure of the expansion tank by its dripping. Then the T&P becomes the last line of defense.

    If code offers no law for pressure protection, and PEX has ratings below 150 psi, the code has failed us.

    http://www.uponor-usa.com/Header/Sys...ller/FAQs.aspx
    Last edited by ballvalve; 01-23-2011 at 01:18 AM.

  3. #18
    Plumber jimbo's Avatar
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    The 130 PSI spec you mention is the recommended maximum normal operating pressure. From the PPFA specifications:

    What are temperature limitations for PEX?
    PEX tubing can be used up to 200° Fahrenheit for heating applications. For plumbing, PEX is limited to 180° F. Temperature limitations are always noted on the print line of the PEX tubing.. PEX systems are tested to and can be used with standard T and P relief valves that operate at 210” F and 150 psi.

  4. #19
    General Engineering Contractor ballvalve's Avatar
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    If you look at uphonor 1/2 " aquapex, which is very commonly used, it only takes 160 psi at 73' F . If its feeding a run away heater, its going to likely blow.

    Its also 120'F at 130psi. Now thats easy to exceed with a bad T&P valve, [ or even with a good t&p valve] I believe. I just do not wish to test for the weak point in a radiant system, especially if its in a slab. Bad enough in a wall.

    I used pex 12 years ago that had even lower ratings.

    I do not understand why a mid line relief valve makes everyone so bent out of shape.

    No one tests new plumbing at 150 psi, so I suggest we never allow the system to get there.



    At 60 pounds pressure, water boils at 307.4 degrees
    At 0 pounds pressure, water boils at 212 degrees
    At 50 pounds pressure, it releases the same energy as two pounds of dynamite.
    Last edited by Terry; 04-03-2011 at 02:49 PM.

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