(206) 949-5683, Top Rated Plumber, Seattle
Results 1 to 14 of 14

Thread: What is considered normal water pressure into a house?

  1. #1
    DIY Junior Member w1ljm's Avatar
    Join Date
    Jan 2006
    Location
    boston
    Posts
    19

    Default What is considered normal water pressure into a house?

    Could someone please tell me what is considered Ie.
    low water pressure? less than 40 psi
    normal water pressure ? between 40 - 65 psi
    or high water pressure? above 65 psi

    into a single family house?

  2. #2
    In the Trades Gary Swart's Avatar
    Join Date
    Sep 2004
    Location
    Yakima WA
    Posts
    7,246

    Default

    Your figures are about right. You do need to remember that pressure and volume are not the same. You can have high pressure but if the pipe is very small or corroded nearly closed, your volume will suffer.

  3. #3
    DIY Junior Member w1ljm's Avatar
    Join Date
    Jan 2006
    Location
    boston
    Posts
    19

    Default Problem with high water pressure into the house.

    My problem is that my hot water heater keeps blowing water out of the safety valve. I have had a expansion tank added to the system years ago and thought it solved the problem,but the problem returned again. Talked to a plumber who stated to make sure that the tank did not go bad (no water leaks out of the air valve when releasing pressure and the tank holds pressure fine) and also check to make sure the tank pressure was equal to the pressure of the water coming into the house. I bought a gauge an measured at the out door faucet, and the drain at the bottom of the hot water tank. They both measured around 90psi.(VERY HIGH) I did bring the pressure of the tank upto be equal, but this seemed to increase the problem. I even tried to drop the pressure any where from 10 -30 psi. Still no change. So I am guessing that the real problem is the high PSI from that street. Is there a pressure reducing valve I can buy and install on the main line coming in to my house???

  4. #4
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    Location
    New England
    Posts
    21,412

    Default

    Pressure reduction valves are fairly common and yes, they are usually installed just after the inlet to the house. Some people do it after the hose bibs because they like the higher pressure for the hoses outside, if that is an option. The expansion tank's pressure will always be the water pressure unless you first turn off the water and drain any pressure in the system by opening a faucet. Then, you can adjust the pressure in the tank. It should be around the inlet water pressure.

    You could have a weak T&P valve or the bladder could still be bad. They usually leak water when you try to add air, though. By dropping the pressure in the thing, you cause it to become stretched too much, which will severely decrease the life of the thing. If it got better and then worse after awhile, it might now be bad.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  5. #5
    In the Trades Gary Swart's Avatar
    Join Date
    Sep 2004
    Location
    Yakima WA
    Posts
    7,246

    Default

    The only reason you even need an expansion tank is if you have a closed system. This is created either by a pressure regulator valve or a check valve built into the water meter. When your water heater heats water, the water expands. In a closed system it has no place to expand to, so when the resulting pressure reaches the TP valve limit, it trips to prevent the heater from bursting. If the system is open, then expansion is absorbed by the water main, but in a closed system, you need an expansion tank. The expansion tank is charged with air at or near the pressure set by the PRV. If the bladder in the tank goes south, then you need a new expansion tank. The TP valve could be faulty, but my money would be on the tank being the problem. Reset the PRV to 60 psi, charge the expansion tank to that pressure, paying attention to the points Jim gave in his reply, and if the tank appears OK, give it a try.

  6. #6
    DIY Junior Member w1ljm's Avatar
    Join Date
    Jan 2006
    Location
    boston
    Posts
    19

    Default High water pressure

    Thanks ! I kind of figured that I would have to shut off the water and drain the system before checking the actual air pressure of the expansion tank. Could you explain how a pressure reduction valve works? I would not think that it works the same as a shut off valve. As reducing the opening would really only reduce the volume of water not the pressure once the system had a chance to stabilize.

  7. #7
    DIY scratch-pad engineer leejosepho's Avatar
    Join Date
    Nov 2006
    Location
    200 miles south of Little Rock
    Posts
    2,474

    Default

    Quote Originally Posted by w1ljm
    Could you explain how a pressure reduction valve works? I would not think that it works the same as a shut off valve ...
    ... and you are correct. A pressure regulator maintains a constant output pressure that is less than the supply pressure ... just like a regulator for an air line or scuba tank. Many RVers carry water-pressure regulators along for their water hookups at high-pressure hydrants, and the one you would need if you decide to install one would be a larger version of that kind of device.

  8. #8
    Plumber jimbo's Avatar
    Join Date
    Aug 2004
    Location
    San Diego
    Posts
    9,001

    Default

    To give a very simplified explanation, a pressure regulator valve uses spring pressure and a diahpragm. It opens or closes down the total flow through the valve in response to varying GPM draw in the house. The net result is that the pressure in the house piping remains more or less at the set pressure.

  9. #9
    Master Plumber Dunbar Plumbing's Avatar
    Join Date
    Apr 2005
    Location
    Northern Kentucky/Greater Cincinnati Area
    Posts
    2,943

    Default

    That expansion tank is probably ruptured/deflated.

    Remove the EXP tank from the system, set the pressure in the bladder only if it was holding pressure before you removed it to 60psi.

    Install the PRV and set it to 60psi, matching the EXP tank.

    Everything that requires water pressure to operate in plumbing was engineered for 60. That is what the pressure should be as a good working pressure going through your house to prevent premature wear or undersupplying flow of water to fixtures.

    I replaced 2 prv's and exp tanks today on a 2 family; both tanks were ruptured because of no prv on the main line and the pressure would crest around 100+ at night. The installers didn't/couldn't set to match the working pressure with that high of a number.....and the tanks state you cannot put more than 85psi in them.

    Imagine how overextended that diaphragm was inside the tank with a factory preset of 40psi and you'll know why it ruptured.
    Read what the end of this sentence means.

  10. #10
    Plumber Cass's Avatar
    Join Date
    Nov 2005
    Location
    Ohio
    Posts
    5,984

    Default

    I would consider 55-75 acceptable. Softeners need a minimum of 35 to operate. Wells commonly operate on a 30-50 pressure swing. I am of the understanding that The utilities in my area, by law, are only required to supply 30PSI.
    Last edited by Cass; 03-29-2007 at 04:10 AM.

  11. #11
    DIY Junior Member w1ljm's Avatar
    Join Date
    Jan 2006
    Location
    boston
    Posts
    19

    Default TP valve on 40 gal hot water heater. BAD???

    1). At what water pressure should a T&P valve start to open?
    There is about 80-85psi in the tank, when is starts to open.
    When it does close, it seals tight.
    2). Is there a way to know if is starting to go bad?
    3). Do they go bad? Weak spring !
    4). Are they easy to replace?
    5). If I have to replace it what Spec's do I need to know when asking for a new one?

  12. #12
    Forum Admin, Expert Plumber Terry's Avatar
    Join Date
    Aug 2004
    Location
    Bothell, Washington
    Posts
    14,202
    Blog Entries
    1

    Default

    Quote Originally Posted by w1ljm View Post
    1). At what water pressure should a T&P valve start to open?
    There is about 80-85psi in the tank, when is starts to open.
    When it does close, it seals tight.
    2). Is there a way to know if is starting to go bad?
    3). Do they go bad? Weak spring !
    4). Are they easy to replace?
    5). If I have to replace it what Spec's do I need to know when asking for a new one?
    T & P valves are set for 150 PSI and 210 degrees.
    If the valve is leaking, it's either too much pressure, a weak spring, too high a temperature, or grit or dirt on the sealing surfaces.

    If the pressure is too high, then a PRV (pressure reducing) valve can fix that. You may need to add an expansion tank.

    Since yours is leaking at a much lower pressure, it may be that the spring has gotten old, or that there is grit preventing a good seal.
    It's fairly easy to replace these. Though if the tank is ten plus years old, it starts getting iffy as to how much money I would throw at it.

    Normal pressure is 40-60 PSI
    Anything over 80 PSI should have a PRV to reduce it down below 80.
    PRV's come preset at 50 PSI
    Last edited by Terry; 02-16-2014 at 06:09 AM.

  13. #13
    Moderator & Master Plumber hj's Avatar
    Join Date
    Aug 2004
    Location
    Cave Creek, Arizona
    Posts
    25,655

    Default

    quote; There is about 80-85psi in the tank, when is starts to open.

    The pressure in the tank is ALWAYS the same as the pressure in the house, unless it was higher than that to start with. Therefore, if your measurement is correct the pressure in the house is 80-85 psi and that is much too low for a T&P valve to open unless it was failing. 90 psi is high, but NOT extraordinarily high. You either have a bad T&P valve, or some other problem that has not been diagnosed yet. I would not consider any pressure under 60 psi as "normal".
    Last edited by hj; 02-16-2014 at 05:28 AM.
    Licensed residential and commercial plumber

  14. #14
    DIYer, not in the trades LLigetfa's Avatar
    Join Date
    Feb 2011
    Location
    NW Ontario, Canada
    Posts
    3,685

    Default

    Quote Originally Posted by Terry View Post
    Since yours is leaking...
    Must be a slow day to dig up a 7 year old thread. Hopefully the OP's T&P valve is not still leaking.

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •