What is considered normal water pressure into a house?

Discussion in 'Plumbing Forum, Professional & DIY Advice, Tips & ' started by w1ljm, Mar 28, 2007.

  1. w1ljm

    w1ljm New Member

    Messages:
    19
    Location:
    boston
    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. Gary Swart

    Gary Swart In the Trades

    Messages:
    7,328
    Location:
    Yakima WA
    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. w1ljm

    w1ljm New Member

    Messages:
    19
    Location:
    boston
    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. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,888
    Location:
    New England
    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.
  5. Gary Swart

    Gary Swart In the Trades

    Messages:
    7,328
    Location:
    Yakima WA
    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. w1ljm

    w1ljm New Member

    Messages:
    19
    Location:
    boston
    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. leejosepho

    leejosepho DIY scratch-pad engineer

    ... 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. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    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. 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.
  10. Cass

    Cass Plumber

    Messages:
    5,980
    Location:
    Ohio
    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: Mar 29, 2007
  11. w1ljm

    w1ljm New Member

    Messages:
    19
    Location:
    boston
    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. Terry

    Terry Administrator Staff Member

    Messages:
    14,889
    Location:
    Bothell, Washington
    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: Feb 16, 2014
  13. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,481
    Location:
    Cave Creek, Arizona
    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: Feb 16, 2014
  14. LLigetfa

    LLigetfa DIYer, not in the trades

    Messages:
    3,895
    Location:
    NW Ontario, Canada
    Must be a slow day to dig up a 7 year old thread. Hopefully the OP's T&P valve is not still leaking.
Similar Threads: considered normal
Forum Title Date
Plumbing Forum, Professional & DIY Advice, Tips & What is considered plumbing rough-in? May 6, 2013
Plumbing Forum, Professional & DIY Advice, Tips & are faucets and diverters considered plumbing"FIXTURES" ? Aug 9, 2011
Plumbing Forum, Professional & DIY Advice, Tips & Is a tub/shower considered a tub, or shower? Mar 24, 2006
Plumbing Forum, Professional & DIY Advice, Tips & garbage disposal problem, or normal? Apr 6, 2014
Plumbing Forum, Professional & DIY Advice, Tips & Is this normal behavior? - Hot Water Tank Pressure Release Valve Nov 9, 2013

Share This Page