Expansion tank – replace? Repair?

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    • #273970
      Anonymous

      Thanks for reading this.

      Nine years ago, my father designed, and I installed, a new multizonned FHW furnace in my house. He was a plumber. I’m not.

      The system is a “classic” design:

      • Three zones, each with its own circulator.
      • No zone valves (my dad hated them).
      • Backflow valves on the supplies.
      • 30 PSI Overflow valve
      • 10-15 PSI inlet regulator (Watts S1168F)
      • Circulators are on returns, mounted at furnace.

      I did, however, make a change when I installed the system: my dad bought a membrane take and air fitting, but I convinced him to let me reuse the overhead steel tank for expansion. It’s connected to the back of one of the backflow valves.

      Until last year, everything was fine: then, the high preasure valve started to weep about once a month. Draining the expansion tank would cure the problem for a while: last month, I found and fixed a pinhole in one of the pipes, where another line was rubbing it.

      Now, some questions:

      1. Would a pinhole leak allow the system preasure to climb above the input valve’s setting? How?
      2. Why would the overflow valve weep if the input preasure is regulated at 15 PSI? Does this prove the input regulator is defective?
      3. Can I continue to use the steel expansion tank if I put an Adtrol valve on it to prevent convection? What’s the lifespan of a typical steel tank?
      4. I still have the original membrane tank. Will it be usable after nine years in the box?

        • Can it be mounted upside down, or sideways? The pipes are close in to the furnace, so I can’t “hang” it from the air fitting.
        • If I have to mount it “hanging”, how far from the furnace may I place it?

      5. If I put a preasure gauge on the furnace, where should it be, and what are the most reliable models?

      Thanks again: I appreciate the help. Feel free to email me directly.

      The Old Apprentice
      [Edited by Old Apprentice on 26 November 2000]

    • #288925

      Your system is, indeed, an old classic – with its usual problems. Your present problem began with the leak at the pipe and ends with its repair. There is a long-winded explanation why this occurs. In short, the leak hole made another expansion tank so air could be drawn into the system as water was forced into the existing expansion tank. A more complete explanation can be read at http://www.hydronic.net
      at the Lessons section under ‘Make a Positive Pressure’
      The extra volume of air causes the relief valve weeping as the system water heats up. Your Dad’s system worked for many years while there was no leak, so the bladder expansion tank change is not necessary. There should be a gauge on the boiler (furnace means warm air appliance) so the old gauge should be replaced with the new at that location.

      The existing expansion tank is also called an air control tank. It is placed at that location to trap any air in the system and act as an air scoop to catch the air bubbles within the sealed system.

      Changing the old tank to the bladder tank changes the system to an air elimination system. The bladder tank is not meant to trap air in the waterside of the system. The air has to be eliminated or vented at a convenient spot, usually at the boiler or an air scoop right off the supply side of the boiler. You can install the bladder expansion tank at any convenient distance, it doesn’t move much water. It is a good idea to place the bladder tank and its piping below the main with no air traps in the line, so air bubbles go back to the system air vent. nIstall the bladder tank with the fitting upwards so bubbles go up the line to the main.

    • #288926

      Would a pinhole leak allow the system preasure to climb above the input valve’s setting? How?

      Answer: By allowing AIR in this system and Air can be compressed unlike water. Compressed air equals pressure build up especially when heated Pressure temperature relationship.

      Why would the overflow valve weep if the input preasure is regulated at 15 PSI? Does this prove the input regulator is defective?

      Answer. Not necessary Check your gage and try the pressure relief valve to make sure it is properly seated Should be tested during the heating season any way.

      Not all systems can work with a 15# pressure setting. That is why the factory setting is around 12 PSI.

      Even @ 12 PSI if the expansion tank is flooded the relief can discharge as the water is heated it expands and needs a place for this expansion

      Can I continue to use the steel expansion tank if I put an Adtrol valve on it to prevent convection? What’s the lifespan of a typical steel tank?

      Answer. As long as your expansion can pass a hydrostatic test and not leak it can last literally over 100 Years depending on water quality and condition of it.

      I still have the original membrane tank. Will it be usable after nine years in the box?

      Answer. I would get a new one PROPERLY Sized for this system. This is not a case of one size fits all

      Can it be mounted upside down, or sideways? The pipes are close in to the furnace, so I can’t “hang” it from the air fitting.

      Answer: Yes any position is OK BUT you should leave aces to the air fill valve in case needed

      If I have to mount it “hanging”, how far from the furnace may I place it?

      Answer: Close to the BOILER is the best place

      If I put a preasure gauge on the furnace, where should it be, and what are the most reliable models?

      By the way it sounds like your Dad did a FANTASTIC JOB as I also HATE “Zone valves” GARBAGE

    • #288927

      Would a pinhole leak allow the system preasure to climb above the input valve’s setting? How?

      Answer: By allowing AIR in this system and Air can be compressed unlike water. Compressed air equals pressure build up especially when heated Pressure temperature relationship.

      Why would the overflow valve weep if the input preasure is regulated at 15 PSI? Does this prove the input regulator is defective?

      Answer. Not necessary Check your gage and try the pressure relief valve to make sure it is properly seated Should be tested during the heating season any way.

      Not all systems can work with a 15# pressure setting. That is why the factory setting is around 12 PSI.

      Even @ 12 PSI if the expansion tank is flooded the relief can discharge as the water is heated it expands and needs a place for this expansion

      Can I continue to use the steel expansion tank if I put an Adtrol valve on it to prevent convection? What’s the lifespan of a typical steel tank?

      Answer. As long as your expansion can pass a hydrostatic test and not leak it can last literally over 100 Years depending on water quality and condition of it.

      I still have the original membrane tank. Will it be usable after nine years in the box?

      Answer. I would get a new one PROPERLY Sized for this system. This is not a case of one size fits all

      Can it be mounted upside down, or sideways? The pipes are close in to the furnace, so I can’t “hang” it from the air fitting.

      Answer: Yes any position is OK BUT you should leave access to the air fill valve in case needed

      If I have to mount it “hanging”, how far from the furnace may I place it?

      Answer: Close to the BOILER is the best place

      If I put a preasure gauge on the furnace, where should it be, and what are the most reliable models?

      By the way it sounds like your Dad did a FANTASTIC JOB as I also HATE “Zone valves” GARBAGE

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