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Expansion tank: which side up?

Ron Schroeder
Ron Schroeder Member Posts: 998
I was afraid for a bit that we were on the same drugs.


  • D107
    D107 Member Posts: 1,849
    recent clammy install drew praise for upside down tank

    From big Al: "Also good to see someone else that uses gravity with the expansion tank physics rather than against it."

    Is this the accepted method? I see alot done with the connection on top. Is that because if it hangs below the pipe it's easier to install the air vent right above it? Or easier to support when it's placed on/near the ground?

    From the manual:
    "Although the EXTROL does not have to be installed at the base of an air purger, this installation is recommended to reduce air in the system and provide a compact installation. Some method of air elimination is required to ensure an oxygen-free system."


  • Brad White_93
    Brad White_93 Member Posts: 12
    Australian Tanks

    That tank installation was a new one to me when I saw it. I think the benefit of "connection side down" was the matter of avoiding sediment settling on the diaphragm. I could not see weight being an issue because a nipple in tension is a strong thing and when inverted at least the tank is bottom-heavy.

    For myself, my tank is sitting in a wok ring (yes, yes it is), on the floor with a braided flexible hose connecting it to the Sprirovent.

    Key to the installation we all know is the proximity to the circulator (the inlet). Connecting to the air separator is convenient but not essential.

    My next installation I think I will put the tank pointing up because, well, let's face it- it is an incredible conversation piece!
  • hr
    hr Member Posts: 6,106
    Prof Eatherton

    has some excellent observations on exp tank mounting. I hope he pipes in.

    I know for a fact non barrier tube takes expansion tanks out quickly, so keeping the O2 out, or away from trouble is important.

    I recall seeing Amtrol, possibly Flexcon? has a new lined tank for hydronic use. I think to be more glycol friendly? I wonder that is it lined similar to the DHW tanks that see potable water.

    Is this a good time to request a nice stainless steel expansion tank :)

    A light brushed finish would be my first choice. Then it would match some of the boilers that are now being offered in stainless steel jacketing.

    hot rod

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  • D107
    D107 Member Posts: 1,849
    'non barrier tube'?

    thanks hot rod, I'm sorry I wish I had enough knowledge to understand that phrase. and keeping the 02 out, that would be done by the air eliminator in the right location? Or is that achieved by installing the tank a certain distance from the inlet (circulator)?

  • Brad White_93
    Brad White_93 Member Posts: 12
    O2 Barrier Tubing...

    Alas, were it so simple as a Spirovent... but Noooooo..

    Oxygen at the molecular level, like all good gasses, wants to go where they are not. They like to travel and be equidistant to their neighbors, spread out.

    In conventional metal pipe systems (iron or copper) the system is essentially air tight, sure but it is also molecularly tight. Gasses do not pass well through metal.

    Plastic tubing on the other hand is much less dense. The molecules are relatively far apart. They hold in water in the liquid phase very nicely, thank you. But when deoxygenated, the O2 in the air we breathe feels left out of the party. A mission to repopulate that water is at hand. Osmosis.

    To an oxygen molecule, plastic is a labrynth. Not quite a seive, but there is room between that long-chained melody we call PEX....

    So absent an oxygen barrier, O2 will creep in over time and cause all kinds of, well, oxydation... And because it is free oxygen (it does not bond with water, a happy Utah marriage between two hydrogen atoms and one oxygen atom), the single oxygen molecule -yes they are twins, those two- go into town, raid the saloon, shoot out the lights, take over the bordello.... need I go on?

    OK I am done now.

  • Tombig_2
    Tombig_2 Member Posts: 231
    EXP Tanks

    Upside down...rightside up..potato...potahto?? I've never installed an "upside down" tank. Here's my first pex connected install. It's barrier tube. Sideways might give me some concern. Brad, your posts are always informative and entertaining to a full time lurker and part time poster. Gidyup!! Pic might be sideways....sorry.
  • Tombig_2
    Tombig_2 Member Posts: 231
    Just thought I'd let you know

    This 300K dedicated snowmelt was squeezed into an equipment room that already had two 90% furnaces and two 50 gal HW heaters. When the DHW's goes bad the HO will use the Ultra and defunct the chimney. The forced air heat....well it might take a few years.....
  • zac_2
    zac_2 Member Posts: 32
    stainless exp tank

    Grundfos has a stainless expansion tank for their SQE submersible pump sytem, in the manual it mentions it can also be used in hydronic systems. I've actually used one on a geo ground loop, trying to keep it non-ferrous a doncha know.
  • ScottMP
    ScottMP Member Posts: 5,884
    Well said Brad

    Allthought I must say it does sound s bit like you went out for a long lunch.

    From a service point, and since there's no good argument from either location camp, I would say it much easier to replace a tank that is full of water and needs replacment. I have seen tanks balancing on thier tips which always seemed redy to loose thier balance and put undo stress on one side or the other.

    I'm in the connection up camp.

    By the way Brad, remind me never to come to your house for Kung Pao Chicken.


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  • Al_19
    Al_19 Member Posts: 170

    I can't find it now, but I believe that Dan wrote once that the correct mounting was based on the fact that the diaphragm is semi-permeable, allowing air to pass through over time. Does anyone recall that, or was I hallucinating ?
  • Ken_40
    Ken_40 Member Posts: 1,320

    I fear...

  • Al_19
    Al_19 Member Posts: 170

    How are you, Ken?
    Thanks for the vote of confidence!
  • ScottMP
    ScottMP Member Posts: 5,884
    It could be Ken

    or it could be a flashback ...

    How you doing Pal.


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  • frank_25
    frank_25 Member Posts: 202

    Think of a worst-case scenerio you guys.................A # 15 or 30 tank mounted with the connection down,(that's up-side down to me) is water-logged and needs to be replaced. The tank was installed to a valve too tightly and the hex of the tank nipple was jammed to the hex of the valve. That leaves enough room to use a 10" wrench w/ a short pry pipe on the end because the electrician ran EMT too close those so many years ago. So now what?? Cut the tank to make it easier for the next step which is jump on a new valve. No big deal. In my forty years in the trade I jumped many a valve ;~) But wait...........that tank is full of water, there is going to be a big mess and cause water flows down, naturally. And I'm under it, naturally. If the tank were mounted the RIGHT way, no mess and easier to handle. But what do I know// I'm just a plumber.
  • D107
    D107 Member Posts: 1,849
    your recollection is somewhat true

    Hot Tech Topics link by Dan, "Why Compression Tanks Waterlog" Dan does mention semi-permeability of the diaphragm. Don't think he talks about connection point up or down though. What is interesting is at the end he mentions the waterlogging prevention device: The B&G Airtrol Tank Fitting. I assume this is still used.

    "...But then came the diaphragm tank. Diaphragm tanks don’t need to be drained, but they do lose their air pressure over time. That’s because the diaphragm is made of rubber, and rubber is a semi-permeable membrane. Gasses will pass through the rubber and into the water at the rate of about 1-psi per year, which is why you should always check the air pressure before you throw away one of these tanks.

    But let’s get back to those steel compression tanks. The air sits on the water like cheese on a pizza. When the circulator runs, it can’t add any water to the tank because the circulator is operating within a closed system. For the circulator to add water to the tank, the circulator would first have to remove some water from the pipes. And if it did that, there would be an empty space in the pipes where the water used to be, and that’s simply not possible. In a similar way, when the circulator runs, it can’t take any water out of the tank and put it into the pipes because the pipes are already filled with water. Since the circulator can neither add nor remove water from that compression tank there won’t be any pumped flow in the line going up to that steel compression tank. With no flow, the water in the tank will be cooler than the water in the pipes because the water in the pipes is passing through the boiler. If you’d like a more detailed explanation of how circulators work in a closed heating system get a copy of my book Pumping Away (and other really cool piping options for hydronic systems). You’ll find it in the Books & More section.

    Okay, now for a bit of science. Gasses will dissolve in liquids in proportion to the pressure and temperature. As water cools, it absorbs air. When water gets hot, it releases air. Now, since the water in the compression tank is relatively cool (compared to the water in the pipes), it will absorb some of the air that’s inside the compression tank. That’s only natural.

    Here’s what happens next. The hot water in the pipes rises by buoyancy into the tank as the cold water in the tank sinks down into the pipes. These flows pass each other in the single line that connects the compression tank to the system piping. We call this "gravity circulation" and it has nothing at all to do with the circulator. It’s just a natural phenomenon. Now watch this. The air that got absorbed up there in the tank eventually winds up in the piping because of this gravity circulation, and once that air-laden water comes up to temperature, the air gets released as bubbles. Those bubbles get pumped out to some radiator where they settle out of the flow because the water’s velocity out there in the system is usually less than it is closer to the circulator’s discharge. Someone winds up venting the radiator. That makes the system pressure drop. The fill valve senses this and opens, allowing fresh water to enter the system. This water goes up into the tank because that’s the only place that can accommodate it. Remember that the pipes are already filled with water.

    So every time this happens, there’s a little less air in the compression tank, and a little more water. That’s how steel compression tanks get waterlogged. The way to prevent it is to use a special fitting that’s designed to stop gravity circulation between the tank and the system piping. Bell & Gossett’s Airtrol Tank Fitting is a good example of what I’m talking about. These things have been around for more than 50 years and they work well. Sometimes, those "old-fashioned" devices deserve a second look, especially if you’re spending a lot of time draining steel compression tanks."

  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928

    B&G Air-Troll Fittings still available and work like a charm with plain compression tanks.
  • D107
    D107 Member Posts: 1,849
    thanks mike--so Air-Troll fittings won't be good with Extrols?

    says 'Do not use with pre-charged diaphragm/bladder tanks'. Extrols are pre-charged, yes?
  • Brad White_93
    Brad White_93 Member Posts: 12
    Most Extrols are pre-charged

    to about 12 psig at the factory, but have a Schraeder valve (bike tire valve) for field adjustment to suit the system pressure. The best tanks are filled with dry nitrogen by the way so as they leak over time into the system at least it is an inert gas.

    Mike is right, the Air-Trol fittings are designed to be used with conventional tanks only. They allow the air from the system to bubble up to the top of the tank versus allowing the air to be redissolved and drawn out the bottom.

    You could use the Air-Trol fitting with a diaphragm type tank but that would be like fitting a bicycle to a fish.
  • Ron Schroeder
    Ron Schroeder Member Posts: 998
    Downside up

    I have been racking my brain, Dan did say I would only retain only 7% of what I learned in a seminar reading probably not much more but at least I have the book to go back to. I also just recently read in one of Dans books that Expansion tanks hang down to keep the air from collecting in the line to the tank ie air out of system and compression tanks on top so air goes back into the tank.
  • Kevin O. Pulver
    Kevin O. Pulver Member Posts: 380

    I believe the IBR manual recommends that the tanks are fitting up to keep air pockets off of the diaphragm- (which might dry it out)
    Whether it matters or not might come down to the old Gil Carlson definition of what a difference really is.
    "... to BE a difference, has to MAKE a difference."
    SO it may make a difference, but how LONG would it take to make a difference? My question is why (according to boiler inspector), my base-mounted tank must be plumbed with copper, (no pex) when there is 11,000 feet of pex in the same system, at the same pressure? Kevin
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928

    They allow the air from the system to bubble up to the top of the tank versus allowing the air to be redissolved and drawn out the bottom

    And it does that by preventing gravity circulation between the system and the tank. While it's impossible for a circulator to move water from the system to the tank (because of the point of no pressure change where the tank connects), gravity can.

    The air-trol has a tube-within-a-tube that extends into the tank. The outer (larger diameter but shorter) tube is cut such that it's always immersed in water. The outer tube is the "return" connection back to the system. The inner (smaller diameter but longer) tube is cut such that it extends into the air space of the tank. The inner tube is the "supply" connection from the system. Because it's in the air and the other is under water, gravity circulation cannot be established.
  • Brad White_93
    Brad White_93 Member Posts: 12
    Nicely said, Mike! (NM)

  • D107
    D107 Member Posts: 1,849
    Consensus seems to be connection side up

    IBR Guide: "Always mount the tank with its system tapping UP, never on its side or upside down. This ensures the diaphragm will always be wet, avoiding cracking due to drying out of the elastomatic." Also as you pros know--but the guys who installed my old Weil McLain in the 80s for the previous owners did NOT know--...'the best place to locate the circulator is with its inlet (suction side) connected near the expansion tank..."

    Bottom line is it seems tanks should be checked periodically and perhaps replaced every _____ years if too much air has escaped. It has also been recommended that a new tank be checked for actual pressure setting before installation. Rule of thumb for sizing, IBR says, is at least one gallaon for each 7000btuh of total heat load. So a 30 gallon tank should handle up to 210Kbtu of heat load, but I think I've heard on the wall it never hurts to be oversized with this. Don't know if fill pressure would have to be adjusted per situation.



    PS Bruce which book was that of Dan's? I may have it.
  • Actually , I think it's alot safer

    to take out a water-logged expansion tank with the schrader valve up . I had a buddy of mine spin a 30 out ( threads up ) , not knowing it was full and he broke 2 fingers .

    Also , when you spin out a full tank with the threads down , you only get a gulp or 2 of water before you can flip it over . I've seen bladder tanks in every postion last decades . We just took a 15 out that was installed in 1979 . It was horizontal and still had a 10 psi air cushion .
  • Ray Landry_2
    Ray Landry_2 Member Posts: 114

    I'm in the IPS side up camp as well. Maybe it's just a force of habbit, but it seems like a sturdier install when you're relying on the wieght of a 1/2 nipple thread versus the weld at the tank to hold a water logged tank. Replacement? I drill a small hole in the tank before I unspin it if it's in a real bad spot.
  • John Ketterman
    John Ketterman Member Posts: 187
    right side up or upside down? maybe this is the answer?

    "The hot water in the pipes rises by buoyancy into the tank as the cold water in the tank [which contains dissolved gases that have passed through the membrane] sinks down into the pipes..."

    The above is from David Goldman's post above, quoting Dan Holohan. If this is the explanation for tank waterlogging, then doesn't it make sense to mount the tank BELOW the fitting? The above quote assumes that hot water in the pipe will rise by bouyancy into the tank. But if the tank is lower, then there can be no convection...
  • Boilerpro_5
    Boilerpro_5 Member Posts: 407
    B and G's recomendation is ...

    to have the tank pointed up, but the connection must not be from the bottom of the heating pipe. This, I believe, is to prevent debris in the system from puncturing the diaphragm. They also want water against that diaphragm. Thier piping diagram shows a take off from the side of the system piping down into a "U" with drain valve (to prevent dirt from reaching the tank), and then an air vent at the tank side of the "U".

  • Tombig_2
    Tombig_2 Member Posts: 231
    Tank pointed up?

    > to have the tank pointed up, but the connection

    > must not be from the bottom of the heating pipe.

    > This, I believe, is to prevent debris in the

    > system from puncturing the diaphragm. They also

    > want water against that diaphragm. Thier piping

    > diagram shows a take off from the side of the

    > system piping down into a "U" with drain valve

    > (to prevent dirt from reaching the tank), and

    > then an air vent at the tank side of the

    > "U".


    > Boilerpro

  • Tombig_2
    Tombig_2 Member Posts: 231
    Pointed Up?

    Alright Dave, I'll bite...

    Do you mean npt threads or schrader (air valve) up? Npt up means water on one side of the diaphragm and air on the other. The other way means air-air. I think as long as it's not mounted sideways to create unequal pressure across the diaphragm it shoudn't matter. I've always been npt up and I believe I always will be unless schooled otherwise. I'm trying to schedule a Woodhaven weekend for July 15-16. Contact me.
  • Connection side up here....

    I know, I know, I've been proven theoretically wrong on this subject before, and I've espoused until I'm blue in the face.

    I've been hanging them from scoops etc for EVER, and never had any issues. Seems like the majority of the failures I've seen on EXP tanks is where they were piped upside down IMPO, but as Ken Secor would say, it is "anecdotal" information. Straight from 33-1/3 years of doing it in the field, but none the less, anecdotal.

    Some manufacturers allow it either way, but for me, my money, my experience and my gut feeling, the threads shold be pointed either up, or horizontally, but never down.

    I'm really not interested in debating it because it was proven to me that some manufacturers say it can be done either way (some people will tell you ANYTHING to get you to buy and install their products) and so be it. I think they're betting on the fact tha the tank will last past its warranty period in that application, and if it DOES cause early failures, its good for sales...

    The structure of the tank is not made to handle the torque and stress it might see mounted with the threads down, and a failed bladder. Been there, seen that, saw the dent in the concrete floor from the tank hitting the deck, DON"T want to see it AGAIN.

  • Boilerpro_5
    Boilerpro_5 Member Posts: 407
    NPT UP ,Tom

  • Kevin O. Pulver
    Kevin O. Pulver Member Posts: 380
    Check again J

    I believe they're talking there about the old "open" tanks, not the new, pressurized diaphragm tanks.
    The open ones had the special fitting on them to prevent what you describe and were only able to be oriented "UP" to my knowledge. The diaphragm tanks give you a choice, thus this long thread... Kevin
  • DanHolohan
    DanHolohan Member, Moderator, Administrator Posts: 16,489
    What they told me.

    This is from Amtrol, and it goes back about 10 years.

    The membrane passes air into the liquid and the tank loses about 1 psi each year under the best of circumstances. That's why they give you a place to pump it up (and disconnect it from the system first, please).

    The hotter the water, the faster the air moves through the membrane, and that's why they want the NPT connection up and above the tank. The lower the tank, the less gravity circulation between the hot system water and the tank water, and the longer it takes for the tank to lose its air.
    Retired and loving it.
  • Al_19
    Al_19 Member Posts: 170

    See Ken,

    I wasn't hallucinating!
  • R. Kalia_4
    R. Kalia_4 Member Posts: 18

    See post from Holohan, below.
This discussion has been closed.