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  • #16
    There was a line of fiberglass tanked electric water heaters. Sounded like a good idea except:
    http://www.thetankatwaterheaterrescu...rum3/2845.html

    The 'glass lined' tanks, for both gas and electric heaters, are porcelain lined, but the only thing keeping them from rusting out is the anode rod. A few heat cool cycles and the glass lining is compromised.

    People didn't like the cost of the steel tank heaters, so the chance of selling them a water heater with a stainless steel was remote, never heard of one anyway. They might be out there though...

    In our area with water hardness around 20+ grains I get about 10-12 years out of a water heater. No point buying the longer warranty, I just buy scratch and dents when I can. If I changed the anodes out every 5 years or so the tanks would last a lot longer... just lazy.

    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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    • #17
      Originally posted by Bob Fisher View Post
      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.
      Should do, but then, boiling point is higher under pressure..... So when a hole develops, the pressure is released, and steam can be generated as the pressure drops.

      What can happen is that the tank turns into a "water rocket", blasting off as it ejects water from the hole. Was very common with old vertical type boilers before certification.... the fire end tube sheet would develop a hole or crack, and off they went. They could travel for blocks.
      1601

      Keep eye on ball.
      Hashim Khan

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      • #18
        I think 2 PRVs are required in the UK, one on the tank, one on a pipe venting outside, the outside one blows first, if that fails the fusible tank one backs it up
        Boilers have 2 also
        Mark

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        • #19
          For those able & interested, Rheem has the fiberglass heater of which I mentioned. Seen at the Home D. Orange Box store. It is of course, electric.
          gvasale

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          • #20
            Originally posted by Cuttings View Post
            Now that most houses have pressure reducing valves in the inlet water line from the street
            Really? That must fail a lot and when it does, it must be a fabulous disaster, pop all the pipes in all the walls like overcooked bratwursts, completely ruined insulation and wallboard, then the mold sets in, etc. Total house loss, from one boring clogged open valve.

            I'm not saying its impossible, people do a lot of stupid things with houses, I live in one with a partial flat roof, but still, geeze.

            I've never lived in a house with a valve like that, so if a old fashioned tank failed "on" it would merely fill with steam at the same pressure as the supply water. I suspect given the poor conductivity of steam an electric element would quickly burn out in steam, but a gas one might overheat and crack the firetube, although then its not going to be an impressive boiling water explosion but a very boring low pressure steam leak. Followed by a most impressive flood and that probably followed by a natgas leak or electricity electrocution. Isn't obsolete technology like giant water tanks fun?

            I've had tankless for more than a decade now and giant tanks as an idea are thankfully dying and going away, so its all a moot point. Never gonna have an old fashioned tank again.

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            • #21
              Tanks may have to have relief valves but after 10 or so years how many of them still work right.
              The shortest distance between two points is a circle of infinite diameter.

              Bluewater Model Engineering Society at https://sites.google.com/site/bluewatermes/

              Southwestern Ontario. Canada

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              • #22
                Originally posted by vincemulhollon View Post
                Really? That must fail a lot and when it does, it must be a fabulous disaster, pop all the pipes in all the walls like overcooked bratwursts, completely ruined insulation and wallboard, then the mold sets in, etc. Total house loss, from one boring clogged open valve.

                Isn't obsolete technology like giant water tanks fun?

                I've had tankless for more than a decade now and giant tanks as an idea are thankfully dying and going away, so its all a moot point. Never gonna have an old fashioned tank again.
                I am not a plumber and have never played one on TV, but I did commercial HVAC work for about 25 years. Seldom will you find a PRV (pressure reducing valve) in the building water supply line, what you will find is a backflow preventer required now by Code in many locations. These valves have cleanable filter screens and internal check valves and in commercial buildings are required to be tested on a regular schedule. Modern plumbing installed to Code will usually not fail do to overpressure. Your dishwasher, washing machine and etc. will however.
                Boilers have PRV's installed to limit the amount of pressure in the system, they also have relief valves in that water line feeding the boiler and of course the boiler relief valve. They are also required to have backflow preventers.
                Retired - Journeyman Refrigeration Pipefitter - Master Electrician - Fine Line Automation CNC 4x4 Router

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                • #23
                  I would hazard to guess that pressure reducing valves and back flow preventers are as common as your municipal water supply is in moving forward with enhancements. I live in a 300 house development where the houses are about 14 years old and on the Raleigh municipal water system. Back in 1998 when the houses were built they had back flow preventers so you couldn't contaminate the municipal water system.

                  We also have adjustable pressure regulators on the line where it comes into the house because the municipal supply is probably in the 80-90 psi range and the regulator is at around 50 psi.

                  Lastly we have about a 5 gallon air bladder tank mounted right on the hot water output of the HW tank to compensate for water expansion as the water in the tank/system heats up.

                  We also have your everyday HW tank relief valve plumbed right into the side of the HW tank.

                  Pretty sure all 4 are code requirements.

                  To answer Daveb's question, no our tanks don't heat the water to boiling. On electric tanks there are adjustable surface sensors you can set to some reasonable temperature. Typically 120F or lower. How many you have depends on how many heating elements. Most tanks have 2. Real small tanks have one. Typically the elements are wired so only one can be on at any given time.

                  If the tank is heated with natural gas or propane then there is a dip tube in the side of the tank near the bottom that senses water temperature and controls the burner. Again, a typical setting might be 120F.

                  I don't think any of the mechanisms allow setting above about 160F.
                  Last edited by dave5605; 12-31-2013, 01:38 PM.

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                  • #24
                    Thanks for the info. It seems your domestic water is all mains fed. The older stuff over here uses a 50 gallon storage tank in the loft, there's a gravity feed from this to a hot water tank (50 Gallon copper cylinder) with coil from boiler and electric immersion heater. The hot water tank is vented to atmosphere by a vent pipe teed into the hot water take off, this drops any overflow back into the cold water tank. Drinking water only comes direct off the mains.
                    Newer systems use a combination boiler which runs the central heating system and provides hot water on demand, no hot water tank necessary with these but no back up if the boiler fails. Most new central heading system are sealed (closed circuit) and have expansion vessels and pressure relief valves. Pressure reducing valves work only when the water is flowing, they don't stop the pressure building up once the flow stops.
                    Dave

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                    • #25
                      If your pressure reducing valve is working correctly it will stop pressure from building up on the downstream side under no flow circumstances. If it's faulty due to a bad seal or dirty seat, then no.

                      There are "through hole" type pressure reducing units like those used on low pressure irrigation systems, but these reduce pressure by volume restriction and by inducing back pressure. None of these can be used in a situation where flow isn't continuous, such as a house/building.

                      My house has a diaphragm pressure regulator - pegged at 60psi, flow or not; Inlet is 93psi. If it allowed the 93 to pass, it would be pressuring my relief tank and everything else - bad news. The commercial buildings I deal with have 135-150psi in... no way that's allowed past the regulator valve.

                      I just replaced the seal in my Dad's pressure reducing valve in NZ (ha, vacation... son, can you fix xxxxx?). A tiny valve seat leak was raising downstream pressure in his tank so the hot side pressure relief valve was releasing water (dribbles) into the exit pipe and his garden. Their house is 12 years old - has a inlet pressure reducer, cold side pressure relief, expansion tank, hot side pressure relief AND hot side mixer to keep domestic hot water temp below 125F. And all they have is a hot water heater - no boiler. Way too complex... nanny state codes. Their old house (1960) had a cold water attic tank that fed the hot water cylinder. The HW cylinder had a vertical pipe that vented to the roof. If the thermostat stuck, there would be a geyser of boiling waters/team straight up from the roof. Saw it often in the city as kid.
                      Last edited by lakeside53; 12-31-2013, 04:26 PM.

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                      • #26
                        That's why you are supposed to check them yearly.

                        JL................
                        Originally posted by loose nut View Post
                        Tanks may have to have relief valves but after 10 or so years how many of them still work right.

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                        • #27
                          Originally posted by dave5605 View Post





                          We also have your everyday HW tank relief valve plumbed right into the side of the HW tank.






                          Yep, code requirement, and even if not, the safest place for the T&PR valve is preferably mounted in the top of the tank, or very near the top on the side.
                          Years past, some would install the T&PR in the outlet piping. To meet code, the thermal expansion sensor (usually an extended plastic tab attached to the valve seat) must project INTO the tank.
                          People with acidic well water should replace the TP&R every couple years.

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                          • #28
                            You will find very few PRV's installed in the flat land areas of the prairies, as here in Iowa. Most of our problems with water pressure deals with not enough. Any PRV will fail with time and should have a relief valve installed downstream like I noted for boiler piping above.
                            Retired - Journeyman Refrigeration Pipefitter - Master Electrician - Fine Line Automation CNC 4x4 Router

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