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Hot Water Tank ?????

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  • Hot Water Tank ?????

    I'm wondering if anyone out there knows how long hot water tanks have had pressure relief valves on them.
    I can't ever remember seeing one that didn't have a safety valve on it. I'm pretty sure it's a law that they do. My reason for asking is last week I walked down into my aunts basement and there was bit of a flood. I noticed that water was dripping out of a small relief valve that was mounted on the out put (hot) line of the tank. I know this thing has been there ever since I can remember, as it's part of the original plumbing (iron pipe) but I never paid much attention to it. The safety valve on the tank was fine, there is no need for two safety valves on the tank so I removed the leaky one and put a plug in it's place.

    The only thing I can think of is in the old days when hot water tanks were first introduced to houses they didn't have safety valves on them and it was up to the installer or plumber to put one in the line. The tank has probably been replaced sever times over the last 70 years or so and the lazy plumbers probably just left it there not wanting to go further back into the original plumbing.
    Any one have any thoughts???

    JL.....................

  • #2
    Sounds logical to me. You ought to post your location though as plumbing practices have varied throughout the world.
    "Patriotism is the last refuge of a scoundrel"

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    • #3
      The TV show "Ask This Old House" showed what happens when someone puts a plug in the outlet of a relief valve on an electric water heater. Not only was the house totally destroyed, but it damaged the neighbors house too! They found the tank, three blocks over! Must of frightened someone when it landed.

      Ed P
      Last edited by Ed P; 12-31-2013, 02:39 PM.

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      • #4
        Originally posted by Ed P View Post
        The TV show "Ask This Old House" showed what happens when someone puts a pug in the outlet of a relief valve on an electric water heater. Not only was the house totally destroyed, but it damaged the neighbors house too! They found the tank, three blocks over! Must of frightened someone when it landed.

        Ed P
        My brother has a pug he would love to get rid of because that dog is such a pain in the ass and ugly as hell. I will show him your post and maybe it will give him some ideas.

        Steve

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        • #5
          A couple of thoughts.
          Now that most houses have pressure reducing valves in the inlet water line from the street it is essential to have a pressure relief valve.
          The pressure reducing valve also acts like a check valve and will not let water go back into the inlet line, thus if the hot water tank was full of cold water then heated without using any water from the house side of the system
          it could build a lot of pressure do to the expansion from heating.
          Also I believe the pressure relief valve on the hot water tank is also a high temperature relief valve to let some water out if the thermostat were to malfunction and continue heating the water.
          Larry - west coast of Canada

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          • #6
            'This Old House'?? Was it not 'Mythbusters', put together by those two clowns in San Francisco'

            Never thought to ask the question outloud, in front of people with real life experience, but if a standard everyday hot water tank is filled with water, sealed off on any/all inlets/outlets and now heated with either a gas burner or an electric element, what happens???????????

            Mythbusters 'demonstrated' a complete disaster. I'm saying rigged.

            --G
            Last edited by Guido; 12-30-2013, 07:02 PM. Reason: Wrong spelling

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            • #7
              Gents, it seems your water tanks are made of the same stuff that cars and fuse panels (as depicted by Hollywood) are.
              Do your water heaters raise the temperature beyond boiling point in a sealed tank? Are you talking about a steam explosion?
              Dave

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              • #8
                Very old systems did not have a temperature and pressure relief valve, only required a pressure relief. The pressure relief you saw was likely very old, and when the heater was replaced the installer put in a code required temperature and pressure relief valve and left the old one. If it wasn't leaking at the time there was no need to remove it.

                If the tank was completly filled with water, and the heater elements were powered up the temperature would continue to rise and the water would continue to expand until the pressure burst the tank. At that point the water flashes into stream and the fun begins...

                paul
                paul
                ARS W9PCS

                Esto Vigilans

                Remember, just because you can doesn't mean you should...
                but you may have to

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                • #9
                  I see no problem, you removed and old, leaky pressure relief valve, but you left the tank-mounted T/P valve. That's the ONLY safety valve in most modern installations, so you didn't create any danger. I do agree with the necessity for the T/P valve, as a water heater CAN explode if the heat source doesn't shut off when it should.

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                  • #10
                    I would think that IF the tank is completely filled and no water is allowed in or out, that as the temp increases and the water expands, the tank would rupture and relieve the pressure. That should happen Long before the temp is high enough to flash to steam. Bob.

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                    • #11
                      Originally posted by Daveb View Post
                      Gents, it seems your water tanks are made of the same stuff that cars and fuse panels (as depicted by Hollywood) are.
                      Do your water heaters raise the temperature beyond boiling point in a sealed tank? Are you talking about a steam explosion?
                      Dave
                      They are indeed made of steel - that's so that they will rust out every few years and you have to keep buying new ones so the tank makers make more money - unlike in the UK where you have (or used to have) the intelligent idea of using copper for the tank.
                      "Patriotism is the last refuge of a scoundrel"

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                      • #12
                        Yes, I did remove the leaky relief valve that was in the hot line. I made sure the one on the tank was working and I flushed it, it's not clogged or stuck. The one on the line had no flip lever, it was just a small brass valve with a flat plastic top. I saw no need to put another such valve in the line.

                        JL.....................
                        Originally posted by jdunmyer View Post
                        I see no problem, you removed and old, leaky pressure relief valve, but you left the tank-mounted T/P valve. That's the ONLY safety valve in most modern installations, so you didn't create any danger. I do agree with the necessity for the T/P valve, as a water heater CAN explode if the heat source doesn't shut off when it should.

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                        • #13
                          Copper lined tanks are not common in the USA as far as I know. I've seen two in my liferime so far, 64 years. But then, I'm not a plummer either. The copper lining was not very thick. I cut them up for scrap, one a few months ago, the other probably 2 decades ago.

                          Many tanks are "stone lined" whatever that means. Now there are fiberglass lined tanks. I've not seen stainless steel.
                          gvasale

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                          • #14
                            Fiberglass lined?? Do you mean fiberglass insulated??? How would fiberglass hold up to a flame???

                            JL.......................
                            Originally posted by gvasale View Post
                            Copper lined tanks are not common in the USA as far as I know. I've seen two in my liferime so far, 64 years. But then, I'm not a plummer either. The copper lining was not very thick. I cut them up for scrap, one a few months ago, the other probably 2 decades ago.

                            Many tanks are "stone lined" whatever that means. Now there are fiberglass lined tanks. I've not seen stainless steel.

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                            • #15
                              Originally posted by JoeLee View Post
                              Fiberglass lined?? Do you mean fiberglass insulated??? How would fiberglass hold up to a flame???.
                              I think it's resin impregnated fiberglass on the inside for corrosion protection.

                              US practice does not use storage tanks so entire domestic plumbing is under more pressure than with an open storage tank system. With an open storage tank for house pressure on the hot side (and most of the cold) you don't need a pressure relief valve because the open storage tank provides your pressure relief.
                              "Patriotism is the last refuge of a scoundrel"

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