PRV opening on new tankless..

Discussion in 'Plumbing Forum, Professional & DIY Advice, Tips & ' started by workingona1920, May 17, 2007.

  1. workingona1920

    workingona1920 New Member

    Messages:
    4
    [​IMG]
    T&P Valve for releasing excess pressure.

    I installed a takagi t-k1 on the side of my house. I ran 3/4 copper from the meter to a ball valve and then to the tankless. From the unit I installed a 150 psi PRV exactly as shown in the manual, and continued the 3/4 run to 1 shower, and to the kitchen sink. With everything completed I opened the ball valve about 1/4 of the way to let the water in at a slow rate, within a minute the PRV opened, and remained that way until I shut off the water. Thinking I bought a faulty PRV, I installed another new one, purged the lines, and then shut off the valves in the bathroom and kitchen and noticed the toilet was running. I lifted the float in the toilet and then heard the PRV activate. I plan on checking the pressure today, but I'm baffled since I never opened the ball valve more then a 1/4 of the way, and the pressure was by no means extreme while I was purging the lines. Any advise would be greatly appreciated. Steve.
    Last edited by a moderator: May 17, 2007
  2. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,263
    Location:
    Cave Creek, Arizona
    Prv

    It makes no difference whether the ball valve is full open or a quarter open, the pressure in the line is the same. The only way you could have that problem, especially with two T&P valves, is if the incoming pressure is excessive.
  3. workingona1920

    workingona1920 New Member

    Messages:
    4
    So if the PRV is rated at 150 psi, I have somewhere around that pressure coming in? Is the reason for the medium pressure from the kitchen and shower valves due to the reduction of 3/4" to 1/2"? Thank you. Steve
  4. Gary Swart

    Gary Swart In the Trades

    Messages:
    7,308
    Location:
    Yakima WA
    You can't just guess what your water pressure is. Spend $10 and get a gauge. Put the gauge anywhere on the water supply and check. Pressure is not regulated by reducing the size of the pipe or how far a valve is opened.
  5. workingona1920

    workingona1920 New Member

    Messages:
    4
    Thanks Gary, I'm going to pick up a gauge today, as well as a Pressure Reducing Valve.

    [​IMG]
    Watts 25AUB-Z3 pressure reducing valve
    Should be used with an expansion tank.
    Last edited by a moderator: May 17, 2007
  6. how about a thermal expansion tank???

    I dont want to throw water on this parade...

    I have heard of this problem before withthe Takagis

    and you might need the thermal exp tank too....

    some osrtof water hammer problem through those

    tankless coils can ocur....


    another thing I am wondering about....

    you ran 3/4 into the tankless coil.....

    then 3/4 out again all the way to a shower...


    I think your flow rate would have been better
    suited if you would have reduced the outlet to 1/2.
    because of the volume having to pass through
    that heat exchanger......


    Anyone else out there with better advice about
    the sizeing of the line comming off one of those units......

    please corect my thr=eory if I am wrong...



  7. workingona1920

    workingona1920 New Member

    Messages:
    4
    I bought a pressure gauge today, hooked it up, and it registered beyond the 200 psi mark. I guess I should have taken into consideration that the old galvi lines I replaced with the 3/4 copper were almost completely closed off with rust. I set up 2 pressure reducing valves, and everything is perfect. Just wanted to say thank you for the replys, I really appreciate it.
    Steve
  8. Gary Swart

    Gary Swart In the Trades

    Messages:
    7,308
    Location:
    Yakima WA
    The pressure did not change when you changed from the old galvanized to copper. Pressure remains constant unless it is reduced by a pressure regulator valve. You would not get the volume of water through the old pipes, but the pressure would not change. 200 psi is a God awfully lot of pressure. That would almost certainly damage appliances and fixtures. 60 to 70 psi is about "normal" pressure, and even as low as 40 psi isn't unusual. Check with your city water department and see what they show your main to carry.
  9. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,814
    Location:
    New England
    If the incoming pressure was truely that high, two PRV's in series is essentially required, since that exceeds the capabilities of the ones typically available. But, especially in volume constricted pipes, thermal expansion could increase the incoming pressure after the valves quite a bit, especially in an older house without any flexible supply lines to faucets or toilets (i.e., rigid lines in place). WIth nothing available to balloon a little, you'd get a bigger pressure change on a totally rigid, closed system than a more typical one with flex lines to toilets and sinks. Plus, new PRV's seal is likely better than an older one.
  10. 200 psi is dangerous.....

    If you look at an air compressor
    anything over 150 psi is considered
    dangerous.and says so right on the tool....

    I realize that water and air pressure are two
    different animals, but still that seems way too far out there.................

    many fixtures are not even rated for that kind of pressure....



    you should really call the local
    water company and have that pressure reading
    checked and possibly
    geared down in your neighborhood...
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