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OLD B & G COMPRESSION TANK SIZING..DO I NEED A NEW TANK?

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  • STEVEusaPA
    STEVEusaPA Member Posts: 6,505
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    ww said:

    the autofill valve works...the water valve leading to the autofill valve is closed. it would put 12 lbs into the system if the valve leading to it was on...when i turn on the valve it will fill up the system to 12.

    This is why you are getting air. Because the system pressure drops too low.
    If you're going to bleed radiators, circulator(s) off. Close valve to expansion tank. Get/keep the pressure up, then bleed off.
    Return pressure to where you want it, open up valve to expansion tank.

    There was an error rendering this rich post.

  • ww
    ww Member Posts: 282
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    ok...will try that out...thanks...when i did drain the expansion tank i did it as described and it worked great as per above instructions...so will fine tune it with what you said.
  • ww
    ww Member Posts: 282
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    ok...i took care of the bleeding as instructed...and got air out. i put the system on and when cold the pressure was 12 lbs...it went up to 26 on gauge and started to come out of relief valve...i'm thinking maybe tomorrow will go thru the compression tank procedure as i did before since maybe there wasn't enough cushion in tank since i found alot of air in system. anyone have any comments on this?

    by the way heat came up fine and all radiators hot.
  • ww
    ww Member Posts: 282
    edited February 2020
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    took care of compression tank procedures again as well as the bleeding procedures..the takeaway here is when to close off the valves as per directions...

    and it made a big difference..testing at a few degrees higher heat setting the boiler water pressure went up to a max of 18 lbs from a cold system 12...8 lbs lower than the 26 lbs from yesterday at a few degrees lower and no dripping from the dual valve as was the case before doing this procedure...so will monitor this.

    Conclusions will be made but my first impression is these two procedures must be done together for results...and of course the compression tank must be monitored for possible air loss into the radiators...and the closing and opening of valves in sequence is important for success...will see what happens...and when bleeding the radiators the fill valve must be open so the water reaches the top floor via the dual valve removing all air...with system off...these are my observations...do they sound right? Thanks!
  • ww
    ww Member Posts: 282
    edited November 2020
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    I've managed to take various comments and procedures from here and arrive at success so far for the most part!

    I was just wondering when the procedure to fill the tank with air is used how do you know there is no air in the tank already and what is the procedure to get to that point?

    Just wonder if i take out 5 gallons of water it is replaced with air so hence the question above. Just want to make sure there isn't too much air or water in the tank. Thanks
  • WMno57
    WMno57 Member Posts: 1,280
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    ww said:


    how do you know there is no air in the tank already

    This condition is called "WATERLOGED". At this point there is little to no air cushion at the top of the tank.

    You will know your tank is waterlogged when the psi raises a lot (say 10 to 12 psi) after the boiler runs for half an hour. It's a closed system. As the water gets hotter it expands and squeezes the water cushion on the top of the tank. That air cushion is a spring and sets the pressure in the whole system.
    ww said:


    Just wonder if i take out 5 gallons of water it is replaced with air

    Don't do that.

    Do this:
    Turn off boiler
    Close valve closest to tank
    Drain tank till ALL the water comes out (may need to remove valve at bottom of tank for this)
    Close drain
    Open valve closest to tank

    The above will give you the correctly sized air cushion.
    I DIY.
  • EricPeterson
    EricPeterson Member Posts: 215
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    @WMno57 - so you are saying to drain all the water out of the tank to get the system to a proper state?
    Shouldn't there be some water in the compression tank?
  • WMno57
    WMno57 Member Posts: 1,280
    edited December 2020
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    When you drain all the water out, the tank is filled with air at 0psi. Then close the drain and open the valve to the system. Some water from the system will flow into the tank, giving you a tank about half full of water at about 14 psi and half full of air at about 14psi. This assumes the fill valve from your municipal water is open.

    Air will compress. Water does not compress.
    I DIY.
  • ww
    ww Member Posts: 282
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    are you referring to an expansion tank?
  • Jamie Hall
    Jamie Hall Member Posts: 23,324
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    ww said:

    are you referring to an expansion tank?

    Usually we refer to the style of tank used to control pressure which you have -- in which there is no separation between the air at the top of the tank and the water -- as a compression tank. Usually the variety which separates the two -- either with a diaphragm or a bladder -- is called an expansion tank. Why? Haven't a clue.

    It's useful to keep the distinction in mind, however, as some of the other controls and piping are very different, and if mixed up can cause quite a bit of mischief.

    Ideally, the compression tank will be connected to the system at a relatively high, hot point, often with various devices to collect the air from the system and direct it to the tank. There is also usually a valve -- often automatic -- in the tank to let excess air out.

    The trap, of course, is that the newer expansion tank requires an air eliminator on the system. It is not uncommon for a misguided plumber to put an air eliminator on a system with a compression tank, at which point the tank will waterlog-- and get blamed for the problem.

    The small expansion tanks used in most heating systems are relatively inexpensive, but as systems get larger a compression tank and fittings gets competitive -- and in very large systems, the compression tank will be less expensive -- and more reliable.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • ww
    ww Member Posts: 282
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    exactly...i have a compression tank...not an expansion tank!..thanks for the detailed explanation....and back to the original question....how do you know there is no air in the tank already?
  • WMno57
    WMno57 Member Posts: 1,280
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    ww said:

    are you referring to an expansion tank?

    I was referring to a compression tank, which has no bladder.

    I agree with everything Jamie said.

    This is also an issue with wells and the tanks in those systems. The well tank industry confused many people when bladder tanks came on that market by stating that smaller bladder tanks had the equivalent capacity of larger air over water tanks (another name for a bladder-less tank). Yes and no. I'm not going to attempt to explain it here. It all has to do with gas
    absorbing into liquids. Like the bubbles in carbonated soft drinks.

    My well has an air over water tank. It works for me. There are trade offs. Not sure I would do it again.

    Almost all homeowners will be better off with bladder tanks for both their wells, and their hydronic heat. Assuming the rest of the well or hydronic system is designed for a bladder tank.

    Air and water. "You gotta keep 'em separated" The bladder does a great job of that. Until the bladder or diaphragm fails.
    I DIY.
  • WMno57
    WMno57 Member Posts: 1,280
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    ww said:

    back to the original question....how do you know there is no air in the tank already?

    Again, you would know this waterlogged condition exists because of the behavior of the pressure gage.





    I DIY.
  • WMno57
    WMno57 Member Posts: 1,280
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    I read through the entire thread again and now think I understand your question.

    You are using Ed's procedure from his November 2019 post to suck 5 gallons of air into the tank thru the drain port. But you are not sure what air / water ratio existed in the tank before you perform Ed's procedure.

    My procedure of completely draining the tank and then allowing the system to fill about half the tank with water will give the correct result, no matter what ratio exists to begin with.

    Ed's procedure is faster. Ed's procedure could also be useful for other tasks. Like changing parts in a wet system.
    I DIY.
  • ww
    ww Member Posts: 282
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    ok...i'll try that when i have to drain the tank again...so far so good though...

    yes I am using Ed's post which works great..but that's what i wanted to know...so i can use your procedure to drain the tank..how would you know that the tank fills up half way with water then?...

    some say use 1/3 air and others say 1/2 air...when you drain the tank and refill it that's what i want to know...how can you figure how much water/air is in the tank before starting?

    the only success i had with this situation was using the procedure outlined by Ed in the post..just wondering about the questions i have asked above.
  • WMno57
    WMno57 Member Posts: 1,280
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    Lets travel back in time to the day in the 1950s when your system was installed. The system was cold, empty, and dry. The dead man who did the initial watering turned on the water and let the system fill. The highest point of the system; not the tank, maybe a 2nd floor radiator was left open. When water came out the highest point, the highest point was closed.

    Because the tank does not have a hole on the top, the 0psi air pocket in the tank was trapped and compressed. No math or calculating was done. No before or after measuring of the air / water ratio in the tank was done. Was it 1/3 and 2/3? Was it 1/2 and 1/2? Don't know. Don't need to know. Whatever the ratio was, it worked.

    If you think your tank is water logged, isolate the tank, and drain ALL the water out of the tank. Then open the valve and let the water flow into the tank. The flow into the tank will stop when the pressure, air cushion size, and air / water ratio are correct.
    I DIY.
  • ww
    ww Member Posts: 282
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    thanks for your insight and great explanation on the subject...going back to what i did lines up with what you are saying here as far as emptying the tank. ..

    the no before or after measuring of the air or water was done and it worked...great stuff. sounds like that when the water came out of the top radiator that acted as the pressure gauge as well for setting up the water in the system and the pressure.!

    I appreciate you responding and giving me more knowledge on the subject. i like how you relate what was in the dead men's thoughts and actions. it was nice going to the dead men's seminar in the past too...enjoyed that alot.
  • EricPeterson
    EricPeterson Member Posts: 215
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    I have a three-story house. Assume that all the radiators are bled and there is no air in the system (that I know of anyway).
    Since water is not compressible, I am wondering how draining the tank will work. If the tank contains only air when the valve is opened, and then fills up part way with water, this water cannot be coming from the system (since water is not compressible).
    Or will air be sucked from the tank, displacing water, and then make its way to the highest point in the system (meaning radiators would then need to be bled)?
    Another point is whether this should be done when the water in the system is cold or hot? I would think cold since water, though incompressible, does increase in volume when heated.
    I do have a fill valve but it adds water very slowly....
  • ww
    ww Member Posts: 282
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    always bleed cold...furthest radiator from boiler on top floor is bled first...that's what i've researched and have done..and it works..the compression tank comes in when water is heated...
    read this entire post and if you have a compression tank it will guide you on what to do. i've tried it more than once and it works.
  • ww
    ww Member Posts: 282
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    one more thing..we can't assume anything..such as all radiators being bled...there are alot of steps to do before the radiators can be bled.
  • Jamie Hall
    Jamie Hall Member Posts: 23,324
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    Very large compression tanks -- say 2,000 gallons or so used for well pumps or that sort of thing -- will have controls on them to maintain and regulate the air volume. Smaller ones -- such as your heating system -- don't, and don't need them. So long as there is some air in there and some water, you're good to go.

    The procedure of emptying the tank and then connecting it to the system and allowing it to fill enough to compress the air to system pressure is completely adequate.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • WMno57
    WMno57 Member Posts: 1,280
    edited December 2020
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    @EricPeterson

    Eric, you stated in another thread that your boiler was made in 2009. WW and I have old systems from the 1950s. I would be amazed if a 2009 boiler is connected to a 1950s style compression tank. I suspect you have a modern style expansion tank. When a modern style expansion tank (also known as an Amtrol, bladder or diaphragm) becomes waterlogged, its time for a new tank.

    The discussion and procedures in this thread only pertain to old style compression tanks. I know nothing about newer systems. If you start a new thread with pictures, others more knowledgeable than I will be able to help.
    I DIY.
  • EricPeterson
    EricPeterson Member Posts: 215
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    @WMno57 - yes I replaced a 1954 boiler with a new one in 2009.
    The original system was gravity, probably coal, upgraded to a natural gas model with a circulator in 1954, but all the original piping was retained.
    My history with this system dates from 1986 when we moved here. I retained the near-boiler piping but added an air separator and repiped it to pump away. I added some more radiators for an addition to the house, and made a few piping changes to split the old part of the house into two zones (1st floor, 2nd/3rd floor) but the gravity volume has essentially been retained for the most part.
    I retained the B&G 24 gallon compression tank. Early on I removed the open expansion tank in the attic from the original gravity install.
    I've tweaked the system over the years (TRVs, zone valves) to make the house comfortable, and added missing components (shutoff valves, backflow preventer, air separator).

    I do have an issue wherein every year there is a fair amount of air to be bled from the system. This air is always present in the radiators on the third floor. Never anywhere else. Thus my interest in this topic. I do from time to time drain some water from the tank and pump some more air into it to get it back up to pressure. I have an inline air separator (B&G) which just now upon close examination I see has been installed BACKWARDS all these years (according to the arrow).
    (to expansion tank)
    ||
    Boiler => (air separator) => (pump) => system
    ||
    (water inlet)
    So I followed advice from Dan's books but made a mistake of putting in the air separator backwards. Fifty-fifty chance.
    I guess I was focused on the "UP" arrow.
    With the heating season in full swing, I am not going to fix this now. Next year I will address it. Hopefully that will address my air situation?


  • WMno57
    WMno57 Member Posts: 1,280
    edited December 2020
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    @EricPeterson

    Some of the things you did in 2009 may be in my future. I assumed a contractor in 2009 replaced everything but the radiators. I get a moderate amount of air each year in my second floor (top floor) radiator (just one, long story).

    If you have an isolation valve before your compression tank, I don't see how air from a drained tank at 0 psi could get into the rest of your system during the tank refill process. The rest of the system would be around 15 psi.

    My guess is the backwards air separator is throwing air out-gassing from the water into the third floor radiators instead of the compression tank.

    I think when you turn the air separator around, air in the top of the tank will absorb into the water in the bottom of the tank. Most of the absorbed air will stay in the cool water in the bottom of the tank. A small amount of water in the bottom of the tank will make its way into the main system, take a couple trips through the system, and then the separator will do its thing and throw the air back into the tank.

    Your system deserves its own thread. Has to feel pretty good to build something that gives you heat for 10 years.
    I DIY.
  • EricPeterson
    EricPeterson Member Posts: 215
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    @WMno57 - thanks for your comments.
    My boiler system activities actually date back to 1986 which is when we moved into our current house. My first activity was to replace electric heaters in the family room with CI baseboard radiators on a separate zone to deal with the coldest room in the house at that time. My partner in crime was my father-in-law who later helped me with running pipe to new rooms on the second and third floor when we did an addition in the 90s.
    My perspective is a bit different from pros as I have worked on just one system over a span of now 34 years. It's not always easy being your own engineer in a pro world, for example companies like Burnham (now U. S. Boiler) will not even answer technical questions. On the other hand there are great companies like Supply House which will sell to all - I bought my Burnham boiler from them and they shipped it to my address. All 400+ pounds of it - free shipping. Supply House has also been a great source for parts.
    I discovered The Wall / HeatingHelp.com a long time ago and have found it invaluable in collecting information and knowledge that applies to my system. I also bought a number of Dan's books and also the Sigenthaler book.
    I still have unfinished work...I would like to replace my system bypass loop (just a ball valve) with a thermostatic bypass valve. I would like to setup a backup circuit to run the boiler in case there is a power outage. I would like to devise a remote monitoring setup so I can make sure the boiler / heating system is OK if we go away for the winter. I should replace my now 30+ year old zone valves. I have an Airtrol that I need to install in the compression tank, and finally I need to reinstall my air separator so it is facing the correct direction.
    But for now everything is working fine and the house is quite comfortable.
  • ww
    ww Member Posts: 282
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    sounds like you have had to learn alot of things as well...from all different sources too. ..i looked in a bell and gossett catalog and they show diagrams of compression tanks....mine has no airtrol either...and they say the pipe has to be 3/4's and mine is 1/2...some things don't look exactly like the manual though...you can look at the photos attached here and see how it compares with yours.
  • EricPeterson
    EricPeterson Member Posts: 215
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    @ww - I bought an Airtrol with a 1/2 fitting that matches my compression tank which is also 1/2". Airtrol is model ATF-12.
    I don't know who says pipe has to be 3/4 - if you mean the pipe from the boiler to the tank well mine is 1" copper for most of the run with a reduction near the tank to 1/2".
    Don't know what attached photos you are referring to.
  • ww
    ww Member Posts: 282
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    go to page one of this post and see photos. there was a diagram in b and g brochure that says the pipe has to be 3/4 inch.
  • ww
    ww Member Posts: 282
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    the connection from the boiler to my tank is 1/2 inch...i don't have an airtrol though...it says it has to be 3/4 below here and also in b and g manual when connecting airtrol...always thought that no airtrol could be a problem...maybe gauge inaccurate...who knows...would like to pick up some of these parts somewhere from someone getting rid of a boiler.



    Airtrol Tank Fittings help establish the proper initial liquid level in the compression tank when filling the hydronic system. They help maintain proper system pressurization by directing released air to the compression tank during system operation and permit cooler liquid flow to the boiler during the off cycle as system liquid cools. Airtrol Tank Fittings must be used with the appropriately sized In-Line Airtrol or Rolairtrol air separator. Tank Connection is 1/2" Male, Boiler Connection is 3/4" Female.
  • EricPeterson
    EricPeterson Member Posts: 215
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    @ww - Well as best I understand it, there is a 3/4" fitting on top of the IAS (air separator), from there you run a pipe up (and over in my case) to the compression tank - I sized the pipe up on the horizontal run to 1" - then it connects to a 1/2" fitting on the Airtrol which threads into the tank.
  • ww
    ww Member Posts: 282
    edited December 2020
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    ok..but it said in specs that the fitting from airtrol to tank is 1/2 inch male and female is 3/4 inch. i remember i had problems with radiators when the pipes were 1/2 inch so i changed those pipes to 3/4 and flow was much better...that was radiators though...if all works fine on your system then i guess it doesn't much matter...only stating what i read and didn't do it.

    What i'm trying to figure out now is if there could be excess pressure buildup in system if some valves on second floor on not fully open...i'm also checking out a difference in pressure caused by a possible gauge calibration problem...so if pressure increases i'll drain off a bit of water and make notation...and when system cools will go to furthest radiator and open bleeder and see if water comes out.

  • EricPeterson
    EricPeterson Member Posts: 215
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    @ww - remember that in my case the pipes to the system are from the original gravity system and quite large. All the near boiler piping is 1-1/4" and the feeds that branch off are 2", 1-1/2", 1-1/4", and 1". There is even a short section of 3".
    As for the Airtrol, to clarify - the threading into the tank is 1/2", and then 3/4" on the other side of the Airtrol back to the boiler which matches the 3/4" on the IAS. As I said I increased the size to 1" on the horizontal run per the B&G instructions.
    I'm not sure this helps with your problem but that's all I know.
  • JUGHNE
    JUGHNE Member Posts: 11,062
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    I just need to point that these postings are tacked onto a 2 year old post.

    The reason for the 3/4" pipe size recommendation from the air collection device to the tank is to aid in the air travel at the top of that piping. That pipe must angle up to the tank so the air can migrate up into the tank....as we know air will migrate upward.
    Then the water can flow back and forth, as it expands and contracts, thru the lower portion of the pipe.

    As stated numerous times a compression tank does not wear out, it only may leak, then it is done.

    A system I maintain still has the original tank from 1961.
    It is a 60 gallon size, when I first came on site there was problems with water logging. Eventually I learned to remove the auto air removal devices and let the tank absorb all the air.
    Also this tank has sight glass on the end. Learned that air loss from the top sight glass valve was an issue. Fixed that problem
    After maybe 5 years tank remains 1/2 water 1/2 air.

  • ww
    ww Member Posts: 282
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    this all sounds great..the moral of the story....don't think just because equipment is old....that it can't perform well and continue service for a long, long time!

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