Holy High Pressure!

Discussion in 'Plumbing Forum, Professional & DIY Advice, Tips & ' started by garyl53, Jun 17, 2007.

  1. garyl53

    garyl53 Engineer

    Messages:
    54
    Location:
    Colorado
    Hi,
    I noticed while investigating a HVAC problem that my Water Heater T&P (temp & pressure) valve was leaving some small amount of water in a bucket I had placed under it after we had finished our basement. I thought maybe that the valve wasn't seating properly or was bad. I searched this great site and learned I should check the water pressure to make sure there wasn't a problem. Well, :eek: , the pressure at the water heater was 115 and actually went up as far as 145 psi or so after showers or washing was done. I called the water department and they said perhaps there was a PRV valve that had gone bad outside, underground, with the water meter. It turns out there is no PRV valve. I now have a new project to add a PRV valve. This is all starting to add up now. I have lived in the house 6 years and I have experienced; a hose blowing off of its threaded connection, two brand new toto toilets experience leaky valves that I had to repair and numerous other small things happen. For some reason I didn't think to check. So I would advise anyone who suspects a problem to buy a PSI meter (<$10) and check to make sure the PRV valve (if you have one) is working correctly.
    Gary
    Last edited: Jun 17, 2007
  2. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,245
    Location:
    Cave Creek, Arizona
    pressure

    It sounds more like thermal expansion if the pressure goes up after the showers when the water heater would be operating.
  3. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,802
    Location:
    New England
    I'd try this...make sure that the water heater is not running, then run the cold tap for say 5-seconds. Then check the water pressure. That would relieve any pressure created by thermal expansion. If it is normal, you don't need a PRV, although it still might be a good idea depending on the normal pressure, but a thermal expansion tank as HJ indicated.

    There are several things that could cause the house's plumbing to become a closed system: there could be a check valve in the water meter; there could be one added separately; or, you may have a prv installed (which you indicated you did not). If any one or more of those is in place, then with the valves closed, using hot water, the replacement cold water gets heated, the pressure goes up. That's where the expansion tank comes in, it gives that water someplace to go without creating excessive pressure problems.

    If your plumbing is not a closed system, as the water expands from being heated, it goes back out to the city's supply lines to equilize the pressure. It is only a problem when it can't do that. Well, the put check valves in to protect the rest of the water supply, so more and more places are using them...if your houses water got polluted by say a hose sucking water out of a puddle, then it wouldn't get into the system's lines and affect others.
    Last edited: Jun 17, 2007
  4. garyl53

    garyl53 Engineer

    Messages:
    54
    Location:
    Colorado
    Hi,
    I thought I would get the pressure down first and then see if I need an expansion tank. I will try the test you suggested. I didn't see any PRV or check valve installed but there could be one in the water meter. The meter is located underground in my front yard and it is hard to see very well down there.
    Thx,
    Gary
  5. Gary Swart

    Gary Swart In the Trades

    Messages:
    7,298
    Location:
    Yakima WA
    If there is a check valve or PRV anywhere in the system you will absolutely need an expansion tank. From the description of the problem, I would bet there is a check valve in the meter. You should check the static water pressure of you supply. If it is too high, you will damage fixtures and blow hoses.
  6. garyl53

    garyl53 Engineer

    Messages:
    54
    Location:
    Colorado
    Hi All,
    I thought more about your comments so I looked into the specs of a thermal expansion tank (Watts PLT-12) and found that the tanks allow a maximum air pressure of 80psi.

    Note: The normal pre-charge is 40psi. Do not exceed 80psi. If system
    pressure exceeds 80psi it will be necessary to either: A. Add a
    pressure reducing valve to the system or, B. Locate the expansion
    tank in a riser where the static pressure is below 80psi.


    If you allow some safety room and set it up for 60 psi then you can just barely support a 40 gal. water heater with my current static pressure of 110 to 115 psi. My conclusion is that I will need to install both a PRV and a thermal expansion tank in order to have a solid system.

    Do you all agree with this?

    Thanks,
    Gary
  7. Gary Swart

    Gary Swart In the Trades

    Messages:
    7,298
    Location:
    Yakima WA
    I believe you are confusing pressure with flow. Static household pressure should not exceed 60 psi. Static pressure is when all outlets are closed. Now, if you have old, corroded-nearly-closed 1/2" galvanized pipe, you may relying on high pressure to force more water through that pipe, but the problem is, when you are not drawing water, the pressure against fixtures is nearly double what it should be. A thermal expansion tank and a PRV go hand-in-hand because the PRV creates a closed system and a check valve in the water meter also creates a closed system. I would suggest you need a PRV to cut the static pressure down to 60 psi and a thermal expansion tank to take care of the expansion problem.
  8. garyl53

    garyl53 Engineer

    Messages:
    54
    Location:
    Colorado
    The static pressure (measured at a hose bibb) is 110 psi. The water department also tells me that is what they have measured at the street. So I will do both. I was a bit confused if I needed the PRV or just an expansion tank but now I am clear, I need both.
    Thanks,
    Gary
  9. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,802
    Location:
    New England
    Yes, if your real static pressure is that high, you need a PRV and because it is then a closed system, an expansion tank. Sounds like you are near a pump or a water tower. Pressure that high is not good for your fixtures. Your shower won't be quite as invigorating, though.
  10. garyl53

    garyl53 Engineer

    Messages:
    54
    Location:
    Colorado
    Hi,
    Just to close out this thread. I installed both the PRV (set for 70 PSI) and Expansion tank (pre-charged to 70 PSI). Everything is working great. I recorded the highest pressure I have seen over the past 3 weeks at 75 PSI so I assume everything is working correctly. Yes the shower is not quite as invigorating but it is more than satisfactory.
    Thanks for all of the help.
    Gary
  11. Gary Swart

    Gary Swart In the Trades

    Messages:
    7,298
    Location:
    Yakima WA
    Glad to hear you have everything operating normally. I would suggest you lower the pressure settings on the PRV and expansion tank, at least try some lower pressures. I have mine set at 45 psi and I'm quite happy with that. I think anything about 60 is too high, but experiment and find your comfort zone.
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