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closed type expantion tank

burto
burto Member Posts: 7
hi guys,
If you have a closed type expansion tank (usually above or near boiler) shouldn't you not have any air vents on system. And if you see one on a air scoop would you pull it ?

Comments

  • hot_rod
    hot_rod Member Posts: 15,012
    A closed system with a bladder style or diaphragm type tank can, and should have an air vent or purger. The EPDM separation assures there is always a air bubble. this is know as an Air Elimination system

    Plain steel type compression tanks (non-bladder) are air "management" or air "control" systems, they need a means to maintain a trapped air bubble in the tank for expansion. The sight glass on the end is the indicator of the level and presence of the trapped air.

    Excellent reading in the Amtrol Engineering Handbook about more of the specifics of they two types of systems.

    Compression tank type systems may have an air purger, but it needs to move the air up into the tank, needs to manage the air, not remove it.
    B&G Airtrol ™ is one example of a fitting to do that. More info here.

    http://bellgossett.com/hydronic-heatingplumbing-accessories/airtrol-tank-fittings/airtrol-tank-fittings-2/
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Empire_2
    Empire_2 Member Posts: 2,343
    Couldn't have said it any better myself. Good Job. I ran into a system w 2 duel tanks that had the B&G airtrol tubes plugged. Any suggestions Hot Rod?
  • JUGHNE
    JUGHNE Member Posts: 8,930
    I have a system with a plain steel hanging compression and an Airtol fitting on top of the boiler. After removing the air vent on the boiler, waterlogging of the tank was less. Then replacing sight glass gaskets and repacking sight glass valves has kept the tank with 2/3 air fill for 6 months so far.
  • icesailor
    icesailor Member Posts: 7,265
    JUGHNE said:

    I have a system with a plain steel hanging compression and an Airtol fitting on top of the boiler. After removing the air vent on the boiler, waterlogging of the tank was less. Then replacing sight glass gaskets and repacking sight glass valves has kept the tank with 2/3 air fill for 6 months so far.

    The only place I have ever seen compression type tanks is on commercial applications. Good advice about the sight glass gaskets and sight glass valves. Most of the ones I saw had a tank drain fitting to break the vacuum in the tank. The fitting had a plug at the bottom which was supposed to seal tightly into a seat. Like a lot of gas valve type seals, over tightening the plug ruins the seat of the seal and causes a leak. Which allows air to get back down the air tube and out of the plug.

    A very good place to apply acquired skills of Teflon tape and paste.

    Then, there's the ones with the 1/8" NPT plug on the side. Tape it.

    The ones with the double acting valve that you put the hose on and back out tightly until it stops. The vacuum breaker side leaks all the air out. Replace the valve.

  • JUGHNE
    JUGHNE Member Posts: 8,930
    This is a 1961 install. Another air issue is on the pumps which push into the boiler. The lower pump runs most of the time, the back up pump is stacked above the lower main pump. To get some of the air out of main pump, I manually open upper flow check, then loosen the large top cap to bleed air. This gets most of it. Any better ideas? I guess pet cocks on the pump would have been a good idea for manually venting.
  • hot_rod
    hot_rod Member Posts: 15,012
    icesailor said:

    JUGHNE said:

    I have a system with a plain steel hanging compression and an Airtol fitting on top of the boiler. After removing the air vent on the boiler, waterlogging of the tank was less. Then replacing sight glass gaskets and repacking sight glass valves has kept the tank with 2/3 air fill for 6 months so far.

    The only place I have ever seen compression type tanks is on commercial applications. Good advice about the sight glass gaskets and sight glass valves. Most of the ones I saw had a tank drain fitting to break the vacuum in the tank. The fitting had a plug at the bottom which was supposed to seal tightly into a seat. Like a lot of gas valve type seals, over tightening the plug ruins the seat of the seal and causes a leak. Which allows air to get back down the air tube and out of the plug.

    A very good place to apply acquired skills of Teflon tape and paste.

    Then, there's the ones with the 1/8" NPT plug on the side. Tape it.

    The ones with the double acting valve that you put the hose on and back out tightly until it stops. The vacuum breaker side leaks all the air out. Replace the valve.

    The Extrol brand expansion tank is only 60 years old. I remember working with my dad in the 1960 and hanging steel compression tanks in all the residential jobs. I suspect some are still in operations.

    Supply houses still sell the small ones, must be a replacement market.

    They do make for a nice drainback solar tank with all those connections :)
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • JUGHNE
    JUGHNE Member Posts: 8,930
    Apparently the steel compression tank has longevity as the one I speak of has a 1960 date on it.....I wonder how may Extrol tanks would we have gone thru since then or not. (54 years).
  • icesailor
    icesailor Member Posts: 7,265
    edited January 2015
    The steel tanks for commercial applications need to be ASME tanks. Very expensive. ASME rated Extrol tanks are expensive too, but a fraction of the cost and no headaches.

    Unless you don't read the instructions. A common problem today.

    RTFIM!!!

    The one I dealt with was installed in 1980. I never noticed a ASME stamp on it. It might have been in the spec's. I just never saw it.
  • JUGHNE
    JUGHNE Member Posts: 8,930
    The old girl from 1960 is ASME "Natl. Bd."... Cat 80.. 60" long 20"OD; I assume 80 gallon. A lot of money then and a lot more today.
    icesailor
  • RobG
    RobG Member Posts: 1,850
    edited January 2015
    icesailor said:


    The one I dealt with was installed in 1980. I never noticed a ASME stamp on it. It might have been in the spec's. I just never saw it.

    Ice, did you not RTFIM? ;)
  • JUGHNE
    JUGHNE Member Posts: 8,930
    I thought that too, but didn't want to say. :|
  • Steamhead
    Steamhead Member Posts: 14,832
    I think Icy meant it was already there when he was called to work on that system.

    I actually prefer plain steel tanks, since they do not have any moving parts. When installed with B&G Airtrol tank fittings and properly hooked up to proper air separators, they rarely if ever waterlog. We have a bunch of them in our customer base installed this way, and never have to do anything with them- unlike diaphragm tanks which lose their air charge and whose diaphragms wear out.

    Diaphragm tanks were supposed to be this great time and money saver, but they are an ongoing maintenance issue. I have a hard time seeing the savings there.



    All Steamed Up, Inc.
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting
    RobG
  • icesailor
    icesailor Member Posts: 7,265
    "" Ice, did you not RTFIM? ;) ""

    I said that I SAW it. I didn't install it. You know, noticed and looked at it when I drained it.

    You have to be careful. There's a singer/Songwriter I'm quite fond of. Cheryl Wheeler. She tells a lot of funny stories. She said that one morning, she stopped for breakfast at some little breakfast place in Rural Pennsylvania. While eating her oatmeal, she noticed a sign over the stack of the daily newspaper. The sign said something like "If you look at it, you have to buy it". Cheryl being the amusing person she is, went up to pay her bill and said to the cashier, "I looked at that paper". The cashier looked at her and Cheryl realized that the cashier was computing the cost of the newspaper to her bill. Cheryl explained that she just "Looked" at it. She didn't pick it up and read it, just "looked" at it from her table when she noticed the sign.
    Wording and speaking can be deceiving.
  • hot_rod
    hot_rod Member Posts: 15,012
    Steamhead said:

    I think Icy meant it was already there when he was called to work on that system.

    I actually prefer plain steel tanks, since they do not have any moving parts. When installed with B&G Airtrol tank fittings and properly hooked up to proper air separators, they rarely if ever waterlog. We have a bunch of them in our customer base installed this way, and never have to do anything with them- unlike diaphragm tanks which lose their air charge and whose diaphragms wear out.

    Diaphragm tanks were supposed to be this great time and money saver, but they are an ongoing maintenance issue. I have a hard time seeing the savings there.


    I think the big difference is the thickness of the steel. Anymore the diaphragm tanks feel like tin foil :)

    I notice the radiant versions of expansion tanks now have a coating of some sort, maybe the same as the DHW tanks? That should help the life expectancy.

    I think the main reason some tanks fail is the connection to plastic tubing systems. Even barrier tube allows some O2 ingress. Or undersizing.


    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    icesailor
  • icesailor
    icesailor Member Posts: 7,265
    @Steamhead:

    I completely agree with your observation. about compression tanks.

    The dedicated tank drain I described vents air out of the tube through the tapered plug and waterlogs the tank. On the end of this ASME tank, there is a gauge glass so you can tell what the water level is in the tank. I removed all leakable parts, greased them up and tested them with gas leak detector soap. No leako's.

    It was one of those political situations. Lots of money for high paid executive administration, no money for simple repairs. I used to pre-charge the tank with compressed air to a greater amount of compressed air to make it run longer. I worked there for over 20 years. When the retired Coast Guard Master Chief Engineman retired, they hired a construction supervisor who supervised bridges on the Main Turnpike. He knew far more about hydronics than I did. Any questions he had, he called his buddies in Maine for advice.

    One of many collected reasons for one day just saying, eff this, and I retired.

    They're smart. We're not.