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Thread: expansion tank and TP valve questions

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    DIY Junior Member reed50's Avatar
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    Default expansion tank and TP valve questions

    I had a licensed plumber (checked with the state to make sure) come out and check the expansion tank to make sure it was still working. He said it was fine. He also said that since there was usually always someone home (and using water) that we really didn't need it. (We do have a pressure regulating valve--one with bypass). I asked about checking the TP valve on the water heater and he said he tells people to leave it alone even though the WH manual says to check it once a year. Now I'm really confused. Our old plumber (found out not licensed) always released the TP valve when he worked on the water heater and said we needed the exp tank. How does the average person know who to listen to and what is right when there are 2 different opinions?

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Code requires it. To verify the t&p valve is not frozen shut, you need to open it. It might fail to reseal, and require replacement if you do test.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    In the Trades Gary Swart's Avatar
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    As I understand it, if the PRV has a bypass, the expansion tank is not needed. However, some newer water meters have a check valve in them which would make the expansion tank necessary. I'd test the T/P. If it doesn't close, they are inexpensive and easy to DIY replace. Almost as easy as changing a light bulb except you need a wrench.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    The bypass can only open IF it exceeds the source. So, to keep the pressure constant, use the tank.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    General Engineering Contractor ballvalve's Avatar
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    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
    Last edited by ballvalve; 01-17-2011 at 12:30 AM.

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    In the Trades Jerome2877's Avatar
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    I really don't get the 150 psi rating on the T&P valves.
    Well you have made your point on multiple posts how you feel about expansion tanks and T&P's. The fact is that many places are now requiring expansion tanks and those valves you keep recommending are not ideal for this application and in some case's not allowed (I won't go into this further as we have discussed this in other posts). I don't think you should be giving advice like this to people just because you don't get it!

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    General Engineering Contractor ballvalve's Avatar
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    YOU don't get it. Watts and Apollo valve company get it just fine.

    1] Explain to me why the set point is 150PSI

    2] Detail your objection to a perfectly engineered valve to back-up the failings of a device with the wrong PSI rating, and a bag in a can that is bound to fail.

    Now I know how valveman feels trying to sell his CSV - cycle stop valve- to the narrow minded "do it like gramps" bunch.

    Keep your insurance paid up, because your sink and washer supplies will blow long before 149 PSI
    Last edited by ballvalve; 01-17-2011 at 02:11 AM.

  8. #8
    Retired Defense Industry Engineer jadnashua's Avatar
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    The T&P valve is a safety device that, hopefully, is never needed. Just like the stability control on a vehicle, or a governor, or the anti-lock brakes...it is there if you exceed the normal operational parameters. You should put in your primary device, and maintain it, just like you should with your car's devices, and if you do, you don't have a problem. If you install a PRV and an expansion tank, until something fails, you'll never see any pressure spikes. If you do your due dilligence, you'd notice something failed, and the T&P would save things in the interim. If you want to install a relief valve that is lower, fine. The T&P valve is designed to keep the WH from splitting. ANything else you do is up to you to protect the rest of the system - the T&P valve is NOT designed to protect anything except the WH, although it might. Installing a PRV and expansion tank is one way to protect the whole system, that is both required (in many places) and proven. ANything extra you do is up to you.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    Forum Admin, Expert Plumber Terry's Avatar
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    Ballvalve, that part is a Pressure relief valve. All water heaters have a pressure and a temperature relief valve.
    And like you mention, they only release at 150 PSI.
    It's much better to have an expansion tank to take up excess pressure long before it reaches that point. If pressure is allowed to ramp up to 150 PSI, the flex on the inner tube of the gas water heater is taking a real beating. After a while the flexing back and forth starts to break the welds in the tank, causing premature failure.
    And this is why, for all the non-plumbers out there, that an expansion tank would be "required".
    Even if some of you "don't get it" we do.
    The plumbing code isn't written by Dummies for Dummies. Gee..........I'm feeling pretty smart right about now. But then, I am a plumber!

    Name:  BRV-T_BRV-PEX.jpg
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    Shut off with "pressure" relief. These have a small spring that will release for Relief Valve Pressure Settings: 75, 80, 100 or 125psi http://media.wattswater.com/es-BRV.pdf

    But again, they release water if the pressure gets too high. An expansion tank prevents that from happening in the first place. It gives room for expansion, not letting the system reach that high a pressure.
    Last edited by Terry; 01-17-2011 at 02:02 PM.

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    General Engineering Contractor ballvalve's Avatar
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    Thanks for the photo. Most plumbers probably did not know these existed, including myself until a bit of research. Most seem not to care, so let me try and explain my point. [The "YOU don't get it" was directed to a DIY'r not the plumbing industry]

    As you mentioned, a expansion tank will be stressed at its max at 149PSI, and very likely an older one will break the bladder.

    Then the last resort is the T&P valve, which as we all have seen on videos, the failure thereof cause a missile launch, unless your supply lines hopefully and likely broke first. More than a few homeowners have fixed a leaky T&P with a pipe plug....

    Since maximum pressure safety and water line breaks have been such a subject of threads here, it seems adding a mid level pressure release is a very cost effective move.

    If you have a expansion tank, adding a simple 8$ adjustable relief valve [not the combo shown in your photo] and setting it at 100 PSI, means that the tank takes pressure increases from say 50 to 100 without opening any valves.

    Then if you get to 100, a few tablespoons of water out the valve prevents over stretching the bladder. When that valve fails, the last line of defense is the T&P and your old toilet supply line. If they hold, you might make the evening news.

    Since I have given up on complaining about expansion tanks, I simply propose that a mid-level relief valve preserves their integrity, and makes the 150PSI T&P a true last resort.

    And I do have a few older T&P valves set at 125PSI, a much more reasonable number.

    The safety Guru over in Electrical would love my third level of protection!
    Last edited by ballvalve; 01-18-2011 at 10:32 AM.

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    Master Plumber Redwood's Avatar
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    Quote Originally Posted by ballvalve View Post
    The safety Guru over in Electrical would love my third level of protection!
    Oh Boy...

    Actually with a PRV set at 75 and an expansion tank installed you won't even see the pressure hit 80 psi...

    The T&P valves are 150 psi because that is 1/2 the design test pressure.

    As for the rest of the plumbing failing before 150 psi is reached if that is your experience you should hire an plumber to do the work in your home. I routinely see plumbing systems with T&P valves discharging under pressure without other failures.

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    In the Trades Tom Sawyer's Avatar
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    A lot of plumbers will give all sorts of arguments for not using an expansion tank. The most common is that the system is "open" and the other is that it's a private well system with a well tank that will handle the expansion. The code however makes absolutely no distinction. It plainly says that all fired or indirect pressure vessels have to have an expansion tank.

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    Master Plumber Redwood's Avatar
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    Quote Originally Posted by Tom Sawyer View Post
    The code however makes absolutely no distinction. It plainly says that all fired or indirect pressure vessels have to have an expansion tank.
    I would assume that if that is what your code says that you have smart water that knows when it is in an electric water heater so it expands less and doesn't need an expansion tank....

    Physics don't seem to apply in Michigan if that is what your code states....

  14. #14
    General Engineering Contractor ballvalve's Avatar
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    Quote Originally Posted by Tom Sawyer View Post
    A lot of plumbers will give all sorts of arguments for not using an expansion tank. The most common is that the system is "open" and the other is that it's a private well system with a well tank that will handle the expansion. The code however makes absolutely no distinction. It plainly says that all fired or indirect pressure vessels have to have an expansion tank.
    Never saw a expansion tank in hundreds of homes, and not in the new ones here also. No interest in the bldg. departments regarding them in this part of Cal.

    As for the rest of the plumbing failing before 150 psi is reached if that is your experience you should hire an plumber to do the work in your home. I routinely see plumbing systems with T&P valves discharging under pressure without other failures
    Why test those old washer hoses, and that old toilet valve at 150PSI? If you trust your system at 150 PSI, do you bump up the bldg. depts. test pressure of 50 psi to 150?

    I think plumbers would sweat bullets if that was the law. And as I recall, the tanks are rated for 150PSI max anyway.

    http://www.uponor-usa.com/Header/Sys...ller/FAQs.aspx

    Aquapex 1/2 " of which I have about 3000 feet of in my house, has a pressure rating of 130 PSI at 120' Fahrenheit.

    You want to run that up to 150? And at perhaps boiling point?

    Sure sounds like that 8$ relief valve is a critical item.
    Last edited by ballvalve; 01-22-2011 at 11:02 AM.

  15. #15
    Master Plumber Redwood's Avatar
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    Quote Originally Posted by ballvalve View Post
    You want to run that up to 150?
    No Ballvalve I don't, which is why I install a pressure reducing valve when high pressure warrants it installation on a system and I install expansion tanks when a closed system warrants installation.

    Here is what Bradford White has to say on the subject...

    Service Bulletins
    Discharging Relief Valves
    Model(s) Affected: All Residential & Commercial Units (#105)


    More and more housing developments are being constructed in areas where the local water utility is supplying these projects with extremely high water main distribution pressure. Contractors are installing water pressure reducing valves in the service. These reducing valves are available with or without a back flow check. In the case where the reducing valve does not permit back flow, we have found by tests that for every degree rise in the temperature there is a build up of pressure from 4 to 6 pounds per square inch in the water heater tank. Under these conditions the tank would be subject to a minimum of 240 PSI with a 60 degree rise in water temperature (4 x 60 = 240) and minimum 400 PSI with a 100 degree rise in water temperature (4 x 100 = 400) and since the tank is designed to withstand a test pressure of 300 PSI, it can be easily understood that the tank may very well rupture unless a temperature and pressure relief valve is installed in the water heater.

    Where a temperature and pressure relief valve is used on a water heater installation, as described above, every time the water heater cycles on the relief valve will discharge or drip.

    To correct this problem:

    Replace the water inlet pressure reducing valve with a valve that has a back flow by-pass built into it. This will permit the water to expand back into the main supply when heated.

    Or, if codes require a back flow prevention device a properly sized thermal expansion tank should be installed in the supply side piping of the water heater.

    The above does not only apply to areas with extremely high main distribution water pressure, but will also occur in areas where the utility will require a check valve in front of the water meter, or where codes require backflow prevention devices installed in the water service.

    http://bradfordwhite.com/servicebull...liefvalves.asp
    My Plumbing Works...
    That is because I follow the Plumbing Code and the Manufacturers Installation Instructions and the advice contained in their Service Bulletins....

    While you the engineer cannot even read the manufacturers instructions...

    Important: This is a control device that limits system pressure in the event of thermal expansion. It does not take the place of any safety relief devices that are required by code. If the incoming water pressure exceeds 65psi (448 kPa), a pressure reducing valve must be installed at the service entrance. If the system already contains a pressure reducing valve, be sure it is set no higher than 70psi (483 kPa) under a no-flow condition.
    http://media.wattswater.com/1915307.pdf

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