expansion tank and TP valve questions

Discussion in 'Water Heater Forum, Tanks' started by reed50, Jan 12, 2011.

  1. reed50

    reed50 New Member

    Messages:
    20
    Location:
    tennessee
    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?
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,139
    Location:
    New England
    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.
  3. Gary Swart

    Gary Swart In the Trades

    Messages:
    7,358
    Location:
    Yakima WA
    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.
  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,139
    Location:
    New England
    The bypass can only open IF it exceeds the source. So, to keep the pressure constant, use the tank.
  5. ballvalve

    ballvalve General Engineering Contractor

    Messages:
    3,261
    Location:
    northfork, california
    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_details.asp?pid=564
    Last edited: Jan 17, 2011
  6. Jerome2877

    Jerome2877 In the Trades

    Messages:
    397
    Location:
    BC
    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!
  7. ballvalve

    ballvalve General Engineering Contractor

    Messages:
    3,261
    Location:
    northfork, california
    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: Jan 17, 2011
  8. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,139
    Location:
    New England
    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.
  9. Terry

    Terry Administrator Staff Member

    Messages:
    15,123
    Location:
    Bothell, Washington
    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!

    BRV-T_BRV-PEX.jpg

    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: Jan 17, 2011
  10. ballvalve

    ballvalve General Engineering Contractor

    Messages:
    3,261
    Location:
    northfork, california
    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: Jan 18, 2011
  11. Redwood

    Redwood Master Plumber

    Messages:
    7,450
    Location:
    Connecticut
    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.
  12. Tom Sawyer

    Tom Sawyer In the Trades

    Messages:
    3,227
    Location:
    Maine
    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.
  13. Redwood

    Redwood Master Plumber

    Messages:
    7,450
    Location:
    Connecticut
    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.... :D

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

    ballvalve General Engineering Contractor

    Messages:
    3,261
    Location:
    northfork, california
    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.

    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/Systems/Plumbing/Installer/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: Jan 22, 2011
  15. Redwood

    Redwood Master Plumber

    Messages:
    7,450
    Location:
    Connecticut
    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...

    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...

    http://media.wattswater.com/1915307.pdf
  16. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    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???????
  17. ballvalve

    ballvalve General Engineering Contractor

    Messages:
    3,261
    Location:
    northfork, california
    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/Systems/Plumbing/Installer/FAQs.aspx
    Last edited: Jan 23, 2011
  18. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    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.
  19. ballvalve

    ballvalve General Engineering Contractor

    Messages:
    3,261
    Location:
    northfork, california
    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.

    [video=youtube;5pVQryuKMj8]http://www.youtube.com/watch?v=5pVQryuKMj8[/video]

    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 a moderator: Apr 3, 2011
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