Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Diaphragm expansion tank, ins and outs

Options
hot_rod
hot_rod Member Posts: 22,476
A cutaway of the tank helps explain what goes on inside.

When first installed and pressurized to the exact fill pressure at the tanks location, the diaphragm will be up against the top. Tank will be empty, just like when it comes out of the box.

As the water is heated and starts pushing into the tank the diaphragm starts moving downward. Basically the diaphragm inverts, notice the cutaway pic, at the acceptance volume of the tank. At this point the rubber is not being stretched, it has just flopped from the top of the tank to the bottom. Think of it as a cone of rubber inside.

A common #30 may have a 2.4 gallon acceptance.



IF the tank is undersized, or not pressurized properly the diaphragm will need to stretch to go all the way to the tanks bottom, or past its inverted shape. Past the acceptance volume the diaphragm is stretching, not just inverting.
It can handle this for awhile and eventually the diaphragm will fail. Usually undersizing contributes to short tank life.

27 psi is the max. pressure on a boiler with a 30 lb relief, so the table starts at 27psi. Table 2 shows initial fill of 12 psi, max. of 27psi.

Ideally you would use these charts to determine the correct size tank, which rarely if ever happens with most residential tanks. You need to know the system volume, and the temperature swing, table 1. 50°- 180° temperature rise, the factor .0275, multiplied by the system volume.

The quick sizer charts just ask about boiler BTU size, and type of heat emitters for residential tank sizing.

Someone noticed the #60 tanks have the same acceptance as the #30. This is because the diaphragm is crimped in at the same location inside. The #60 is basically a #30 with an additional center section welded in. However the air bubble in the tank is much larger, which allows the pressure to remain consistent at higher water volumes.

A few hacks, if you had a boiler running up to 180°, and a mixing valve for 100° radiant, you could calculate the volume of the radiant portion and use a different acceptance number. Leading to a smaller tank requirement. If the system held 1000 gallons that may be worth the calculation.

The opposite for solar thermal, considering the collector volume could run up into 300° range.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
SuperTechSTEVEusaPA
«1

Comments

  • SuperTech
    SuperTech Member Posts: 2,205
    Options
    Bob is there any way to tell the difference between a diaphragm expansion tank and a bladder expansion tank? Is one better than the other? 

    I've been using a Milwaukee 12 volt inflator for a few years to check and set expansion tank air pressure.  Last year I finally convinced my boss to buy rechargeable inflators for my coworkers and they have adopted the process that I have learned on this site for charging tanks.  Unfortunately we still find quite a bit of tanks failing and I would like to offer my customers the best replacement expansion tank available.

    We have been using Watts and Amtrol expansion tanks primarily.  I seem to have better luck with Watts so far. 

    Thanks again for sharing your knowledge. 
  • Derheatmeister
    Derheatmeister Member Posts: 1,572
    Options
    Very nice description.. :)
    In the Vaterland I remember the Heating contractors only using a inner gas (Nitrogene) to refill the diaphragm..
    Couple reasons come to mind why:
    1. The Innert gas (Nitrogene) molecule is larger than just regular air and will not penetrate through the diaphragm as easy.This helps keep the diaphragm charged.
    2. The innert gas is less aggressive and will not Oxydize the rubber diaphragm as regular Oxygen will.
    3. Not sure about the Expansion Coefficientcy of Nitrogene vs. Regular air from a compressor ?
    4. If the diaphragm did leak from the "Air side" into the "Wet side" it would be Nitrogen not air,
    Nitrogene will not cause corrosion to the system.
    We have been using Nitrogen for these reasons.
    At the last ISH some manufacturers where offering refill setups using Nitrogene
    Just some of my observations. :|:*

    SuperTech
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,167
    edited April 2023
    Options
    @Derheatmeister, the most important thing about Diaphragm expansion tank, ins and outs. If you lets die luft outs. you lets das wasser ins.

    Also I always like to add this diagram and explanation to any expansion tank discussion.
    https://forum.heatinghelp.com/discussion/comment/1700219#Comment_1700219. This thread from @DanHolohan's podcast How Diaphragm Tanks Came To Be is helpful in understanding why we read the pressure with the tank not connected to the system pressure

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

    DerheatmeisterMad Dog_2SuperTech
  • Derheatmeister
    Derheatmeister Member Posts: 1,572
    Options

    @Derheatmeister, the most important thing about Diaphragm expansion tank, ins and outs. If you lets die luft outs. you lets das wasser ins.

    Also I always like to add this diagram and explanation to any expansion tank discussion.
    https://forum.heatinghelp.com/discussion/comment/1700219#Comment_1700219. This thread from @DanHolohan's podcast How Diaphragm Tanks Came To Be is helpful in understanding why we read the pressure with the tank not connected to the system pressure


    Like your Luft vs.Wasser Germenglish explaination. :D
    EdTheHeaterMan
  • Mad Dog_2
    Mad Dog_2 Member Posts: 7,245
    Options
    Lucky to get 6 years out of any brand these days.  Mad Dog
    SuperTech
  • Jamie Hall
    Jamie Hall Member Posts: 23,650
    Options
    Nitrogen and air will have exactly the same characteristics so far as being in an expansion tank.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,167
    Options

    Nitrogen and air will have exactly the same characteristics so far as being in an expansion tank.

    Oh Yea... Jamie. Try living inside one of those expansion tanks on the AIR side and see how long you last!... Come to think of it, You won't last very long on the water side either.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

    Derheatmeister
  • hot_rod
    hot_rod Member Posts: 22,476
    Options
    SuperTech said:

    Bob is there any way to tell the difference between a diaphragm expansion tank and a bladder expansion tank? Is one better than the other? 

    I've been using a Milwaukee 12 volt inflator for a few years to check and set expansion tank air pressure.  Last year I finally convinced my boss to buy rechargeable inflators for my coworkers and they have adopted the process that I have learned on this site for charging tanks.  Unfortunately we still find quite a bit of tanks failing and I would like to offer my customers the best replacement expansion tank available.

    We have been using Watts and Amtrol expansion tanks primarily.  I seem to have better luck with Watts so far. 

    Thanks again for sharing your knowledge. 

    There are several types of "bag" or bladder tanks. A partial and full acceptance. So the fluid in inside the bag.

    Amtrol has a pro series, built like the thermal tanks that has a coating inside the steel. Intended for radiant systems with O2 ingress. Like non barrier tube systems.

    There are some stainless steel tanks out there also. Zilmet is a potable rated tank. But with a 210° temperature it could be used on hydronics. Not for the weak of pocketbook :)
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    SuperTech
  • hot_rod
    hot_rod Member Posts: 22,476
    Options

    Very nice description.. :)
    In the Vaterland I remember the Heating contractors only using a inner gas (Nitrogene) to refill the diaphragm..
    Couple reasons come to mind why:
    1. The Innert gas (Nitrogene) molecule is larger than just regular air and will not penetrate through the diaphragm as easy.This helps keep the diaphragm charged.
    2. The innert gas is less aggressive and will not Oxydize the rubber diaphragm as regular Oxygen will.
    3. Not sure about the Expansion Coefficientcy of Nitrogene vs. Regular air from a compressor ?
    4. If the diaphragm did leak from the "Air side" into the "Wet side" it would be Nitrogen not air,
    Nitrogene will not cause corrosion to the system.
    We have been using Nitrogen for these reasons.
    At the last ISH some manufacturers where offering refill setups using Nitrogene
    Just some of my observations. :|:*

    Rumors abound that Amtrol may have used nitrogen back in the day? I haven't found anyone to confirm that.
    I believe they use refrigerated air now, cooling the air pulls the moisture out. Like paint shop compressed air.

    I have my tires filled with nitrogen, seem common theses days. Green caps indicate nitrogen at my tire shop.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,167
    Options
    hot_rod said:



    I have my tires filled with nitrogen, seem common theses days. Green caps indicate nitrogen at my tire shop.


    I tried to use carbon dioxide for my tires but I just can't exhale enough pressure to get above about 2 PSI

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • SuperTech
    SuperTech Member Posts: 2,205
    Options
    Are most of the commonly used expansion tanks bladder tanks? I usually come across Amtrol, B&G and Watts tanks. I see some Zilmet? tanks that look a little different, like two halves pressed together to form the tank.

    I'm going to have to ask around to find about the Amtrol Pro tanks. Maybe one of my local distributors carries them.

    The comments about nitrogen are interesting....I might have to experiment with it next time I recharge my tank at home. 
  • SuperTech
    SuperTech Member Posts: 2,205
    Options
    Honestly I wish we could go back to compression tanks with Airtrol fittings. No need for air vents, scoops or anything like that.  Seems like a simpler, better way to do things.
    EdTheHeaterManleonz
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,167
    edited April 2023
    Options
    SuperTech said:

    Honestly I wish we could go back to compression tanks with Airtrol fittings. No need for air vents, scoops or anything like that.  Seems like a simpler, better way to do things.

    Sometimes Old is New. I took my wife to a Rollings Stones Concert before we were married. 20 years later my teenage daughter rushes home form high school one day to tell her mother about this great new rock band called The Rolling Stones. What's Old is New!

    Edit: all I know is... It's only rock n' roll.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • Derheatmeister
    Derheatmeister Member Posts: 1,572
    Options
    SuperTech said:

    Bob is there any way to tell the difference between a diaphragm expansion tank and a bladder expansion tank? Is one better than the other? 

    I've been using a Milwaukee 12 volt inflator for a few years to check and set expansion tank air pressure.  Last year I finally convinced my boss to buy rechargeable inflators for my coworkers and they have adopted the process that I have learned on this site for charging tanks.  Unfortunately we still find quite a bit of tanks failing and I would like to offer my customers the best replacement expansion tank available.

    We have been using Watts and Amtrol expansion tanks primarily.  I seem to have better luck with Watts so far. 

    Thanks again for sharing your knowledge. 

    One thing that was also explained to me was to keep the pressure to the "Wet" side a little higher so that the rubber diaphragm doesn't rub against the inlet...Apparently the repeated rubbing can cause a break in the rubber. :/
    GroundUpSuperTechMikeAmann
  • tim smith
    tim smith Member Posts: 2,774
    Options
    Why not use Natural gas to charge the tanks, then you could put combustible leak detector in room and know that your expansion tanks is low. :)
    SuperTechCLambDerheatmeister
  • Jamie Hall
    Jamie Hall Member Posts: 23,650
    Options
    My point was that in an expansion tank (or, for that matter, at tire...) you are dealing with the physical properties, and both straight air 80% nitrogen) and pure nitrogen are sufficiently far from their boiling points that they both behave as ideal gasses. Nor is pure nitrogen significantly less subject to leakage, since that is governed primarily by molecular weight (Nitrogen, N2, is 28, and air -- 80% nitrogen, 20% oxygen) has a mean molecular weight of about 29.

    I have heard the argument that dry air is better, and -- in principle -- it is, since if the water vapour in the air condenses the volume and thus the pressure will decrease. A little. But that assumes that the air reaches the dew point, and even then the effect is small.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    SuperTechCLambEdTheHeaterMan
  • hot_rod
    hot_rod Member Posts: 22,476
    Options
    Bob is there any way to tell the difference between a diaphragm expansion tank and a bladder expansion tank? Is one better than the other? 

    I've been using a Milwaukee 12 volt inflator for a few years to check and set expansion tank air pressure.  Last year I finally convinced my boss to buy rechargeable inflators for my coworkers and they have adopted the process that I have learned on this site for charging tanks.  Unfortunately we still find quite a bit of tanks failing and I would like to offer my customers the best replacement expansion tank available.

    We have been using Watts and Amtrol expansion tanks primarily.  I seem to have better luck with Watts so far. 

    Thanks again for sharing your knowledge. 
    One thing that was also explained to me was to keep the pressure to the "Wet" side a little higher so that the rubber diaphragm doesn't rub against the inlet...Apparently the repeated rubbing can cause a break in the rubber. :/
    Viessmann Solar taught me about a “safteyseal”

    The fill pressure a couple lbs higher than the tank pre charge. This allows a small amount of fluid into the tank

    when the collector temperature drops down, or way down on a cold  evening the gauge will not drop to zero from the contraction. This helps prevents a panic call that the system has leaked out.
    The Germans  tend to run higher solar pressure also, 4 bar or so. This helps prevent fluid  flashing  when the collectors stagnate. The early PAW solar pump stations we brought over had 6 bar gauges on them, 87 psi!


    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    Derheatmeister
  • RayWohlfarth
    RayWohlfarth Member Posts: 1,554
    Options
    good job @hot_rod I enjoy this thread
    Ray Wohlfarth
    Boiler Lessons
    SuperTech
  • MikeL_2
    MikeL_2 Member Posts: 506
    Options
     Does it matter if hydronic exp tanks are installed upside down? Just in my small world I replace more failed tanks that are installed this way.
  • hot_rod
    hot_rod Member Posts: 22,476
    Options
    MikeL_2 said:

     Does it matter if hydronic exp tanks are installed upside down? Just in my small world I replace more failed tanks that are installed this way.

    Amtrol guide shows horizontal as acceptable. Zilmet shows connection up as preferred, horizontal or connection down as acceptable.

    I don’t know of any official study comparing the various methods and life expectation differences

    I have used the horizontal position often, especially with the larger #60 tanks.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Derheatmeister
    Derheatmeister Member Posts: 1,572
    Options
    tim smith said:

    Why not use Natural gas to charge the tanks, then you could put combustible leak detector in room and know that your expansion tanks is low. :)

    :s:'(:#
    hot_rod said:



    Bob is there any way to tell the difference between a diaphragm expansion tank and a bladder expansion tank? Is one better than the other? 

    I've been using a Milwaukee 12 volt inflator for a few years to check and set expansion tank air pressure.  Last year I finally convinced my boss to buy rechargeable inflators for my coworkers and they have adopted the process that I have learned on this site for charging tanks.  Unfortunately we still find quite a bit of tanks failing and I would like to offer my customers the best replacement expansion tank available.

    We have been using Watts and Amtrol expansion tanks primarily.  I seem to have better luck with Watts so far. 

    Thanks again for sharing your knowledge. 
    One thing that was also explained to me was to keep the pressure to the "Wet" side a little higher so that the rubber diaphragm doesn't rub against the inlet...Apparently the repeated rubbing can cause a break in the rubber. :/

    Viessmann Solar taught me about a “safteyseal”

    The fill pressure a couple lbs higher than the tank pre charge. This allows a small amount of fluid into the tank

    when the collector temperature drops down, or way down on a cold  evening the gauge will not drop to zero from the contraction. This helps prevents a panic call that the system has leaked out.
    The Germans  tend to run higher solar pressure also, 4 bar or so. This helps prevent fluid  flashing  when the collectors stagnate. The early PAW solar pump stations we brought over had 6 bar gauges on them, 87 psi!





    Yes that is a better terminology "Saftey seal"..
    They also use a Vorschaltgefäß which is a pre expansion tank vessel to keep higher temperatures away from the exspansion tank
  • dko
    dko Member Posts: 644
    edited April 2023
    Options
    The only residential (#15, #30 heating, #5, #12 potable) bag type expansion tank that I know of is by Calefactio. Great tanks and the only other expansion tank I now stock other than Amtrol.

    I had cut open almost every residential expansion tank in the market.

    Used to carry Zilmet. Zilmet potable water tanks confuse me. If you see Amtrol's potable water tanks, there is a plastic lining on the tank itself. Zilmet instead lines the bladder with the plastic and the water still contacts the steel. According to their NSF certification, it is a potable water coating on the steel.

    What's the point of using the buytl if you're just going to cover it up? How does it stretch? Water only contacts the plastic lining and steel. A lot more stress on the hoop ring, which is thin to begin with. I have customers bring me back any failed expansion tanks bought from me for warranty. Zilmet tanks for sure have the highest early failure rate and it is almost always hoop ring failure. Thermal fatigue? Ring always comes loose. They are the cheapest for a reason. Everflow (Flextrol) and AF (Granite) are Zilmet relabels.




    SuperTech
  • Jamie Hall
    Jamie Hall Member Posts: 23,650
    Options
    Ideally the butyl -- or other flex material -- shouldn't ever stretch. It should just flex.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • hot_rod
    hot_rod Member Posts: 22,476
    edited April 2023
    Options
    Looks like Wessel still offers small bladder tanks. The ring on the top is the indication.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • SuperTech
    SuperTech Member Posts: 2,205
    Options
    hot_rod said:
     Does it matter if hydronic exp tanks are installed upside down? Just in my small world I replace more failed tanks that are installed this way.
    Amtrol guide shows horizontal as acceptable. Zilmet shows connection up as preferred, horizontal or connection down as acceptable. I don’t know of any official study comparing the various methods and life expectation differences I have used the horizontal position often, especially with the larger #60 tanks.
    I just checked the installation manual for the ST5 and ST-12 potable water expansion tanks and Amtrol states they should be mounted vertically only. The guide for the #30 hydronic expansion tank doesn't state anything except that the tank should be installed on the air purge. 

    I remember looking this up a while back and I thought it was Amtrol who stated that sidewards installation leads to premature tank failure. 

    I just don't like seeing sideways tanks.  Just doesn't look right. 
  • leonz
    leonz Member Posts: 1,183
    edited April 2023
    Options
    SuperTech said:

    Honestly I wish we could go back to compression tanks with Airtrol fittings. No need for air vents, scoops or anything like that.  Seems like a simpler, better way to do things.

    ---------------------------------------------------------------------------------------

    The steel compression tanks work very well. An open to air saddle mounted expansion tank with an
    air-trol valve works just as well and weighs even less as it is not required to hold pressure as the tank is vented with a simple air screen vent.

    It is a blessing to have 5 gallons of air and 10 gallons of water below the air blanket in a compression tank for pressure control.

    A big thank you to the Dead Men and an even bigger thank you to Mr. Dan Holohan.
    SuperTech
  • dko
    dko Member Posts: 644
    Options
    Is there also not a reason why the warranty is only 1 year for stand model expansion tanks (Amtrol ST-30V)? Or merely coincidental with the larger sizes entering commercial use?

    I have always wondered why they would not just weld the stands on the opposite side and have the nipple facing up for the smaller gallons and @hot_rod pointing to Wessels tanks I found they do indeed do this and offer the full 5 year warranty.



  • hot_rod
    hot_rod Member Posts: 22,476
    Options
    leonz said:

    SuperTech said:

    Honestly I wish we could go back to compression tanks with Airtrol fittings. No need for air vents, scoops or anything like that.  Seems like a simpler, better way to do things.

    ---------------------------------------------------------------------------------------

    The steel compression tanks work very well. An open to air saddle mounted expansion tank with an
    air-trol valve works just as well and weighs even less as it is not required to hold pressure as the tank is vented with a simple air screen vent.

    It is a blessing to have 5 gallons of air and 10 gallons of water below the air blanket in a compression tank for pressure control.

    A big thank you to the Dead Men and an even bigger thank you to Mr. Dan Holohan.
    A compression tank might be awkward on a mod con, even newer cast boilers, where would the AirTrol fitting go?

    You would need to add an air separator and run the vent into the tank somehow?

    Last I priced a tank, fittings sight glass, etc it was pushing 900 bucks for a compression tank. For what advantage?

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • SuperTech
    SuperTech Member Posts: 2,205
    Options
    hot_rod said:
    Honestly I wish we could go back to compression tanks with Airtrol fittings. No need for air vents, scoops or anything like that.  Seems like a simpler, better way to do things.
    --------------------------------------------------------------------------------------- The steel compression tanks work very well. An open to air saddle mounted expansion tank with an air-trol valve works just as well and weighs even less as it is not required to hold pressure as the tank is vented with a simple air screen vent. It is a blessing to have 5 gallons of air and 10 gallons of water below the air blanket in a compression tank for pressure control. A big thank you to the Dead Men and an even bigger thank you to Mr. Dan Holohan.
    A compression tank might be awkward on a mod con, even newer cast boilers, where would the AirTrol fitting go? You would need to add an air separator and run the vent into the tank somehow? Last I priced a tank, fittings sight glass, etc it was pushing 900 bucks for a compression tank. For what advantage?
    The advantage of not needing to replace the tank during the lifespan of the boiler.  I'm a service tech who works on a lot of boilers and replaces dozens of failed tanks every year. I don't think my customers would care about a $900 one time expense when they realized how much money they spend on bladder tank, air vent and leaky relief replacements over the years. 
  • dko
    dko Member Posts: 644
    edited April 2023
    Options
    Dozens of failed tanks every year, but how long did the replaced tank last before needing replacement for the individual customer? One in my home is going on 8 years.

    Mechanical rooms are getting smaller and smaller as every square inch becomes more expensive and valuable. We in this field value this differently than others. If a compression tank was specified, your job now would be to find an alternative solution that takes up less space. And that is?

    $900 is 18 years of a $50 expansion tank replaced every year- which is not the case. Your argument should have just been about service charges, not the cost of replacements as it will most definitely be higher than that of the material.

    IMO should thank expansion tank replacements for providing job security.
  • hot_rod
    hot_rod Member Posts: 22,476
    Options
    SuperTech said:


    hot_rod said:

    leonz said:

    SuperTech said:

    Honestly I wish we could go back to compression tanks with Airtrol fittings. No need for air vents, scoops or anything like that.  Seems like a simpler, better way to do things.

    ---------------------------------------------------------------------------------------

    The steel compression tanks work very well. An open to air saddle mounted expansion tank with an
    air-trol valve works just as well and weighs even less as it is not required to hold pressure as the tank is vented with a simple air screen vent.

    It is a blessing to have 5 gallons of air and 10 gallons of water below the air blanket in a compression tank for pressure control.

    A big thank you to the Dead Men and an even bigger thank you to Mr. Dan Holohan.
    A compression tank might be awkward on a mod con, even newer cast boilers, where would the AirTrol fitting go?

    You would need to add an air separator and run the vent into the tank somehow?

    Last I priced a tank, fittings sight glass, etc it was pushing 900 bucks for a compression tank. For what advantage?


    The advantage of not needing to replace the tank during the lifespan of the boiler.  I'm a service tech who works on a lot of boilers and replaces dozens of failed tanks every year. I don't think my customers would care about a $900 one time expense when they realized how much money they spend on bladder tank, air vent and leaky relief replacements over the years. 

    So you do offer them to your customers? How many have you installed in the last year or so?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Jamie Hall
    Jamie Hall Member Posts: 23,650
    Options
    I'm slightly puzzled and would like enlightenment... I have bladder tanks in service (several houses) for domestic water supply (well pump control) and I have only had one fail. It was 50 years old when it gave up (a big Well-X-Trol). What's the difference?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • leonz
    leonz Member Posts: 1,183
    Options
    hot_rod said:

    leonz said:

    SuperTech said:

    Honestly I wish we could go back to compression tanks with Airtrol fittings. No need for air vents, scoops or anything like that.  Seems like a simpler, better way to do things.

    ---------------------------------------------------------------------------------------

    The steel compression tanks work very well. An open to air saddle mounted expansion tank with an
    air-trol valve works just as well and weighs even less as it is not required to hold pressure as the tank is vented with a simple air screen vent.

    It is a blessing to have 5 gallons of air and 10 gallons of water below the air blanket in a compression tank for pressure control.

    A big thank you to the Dead Men and an even bigger thank you to Mr. Dan Holohan.

    ================================================================

    A compression tank might be awkward on a mod con, even newer cast boilers, where would the AirTrol fitting go?

    You would need to add an air separator and run the vent into the tank somehow?

    Last I priced a tank, fittings sight glass, etc it was pushing 900 bucks for a compression tank. For what advantage?

    =================================================================

    You can use an air scoop with a 3/4 inch top tapping if desired and use the top tapping in the air scoop to act as the riser to the airtrol fitting threaded into and under the less expensive steel open to air expansion tank using refrigerant grade copper for the riser pipe to the airtrol valve in the open to air expansion tank whatever distance away from the boiler permits mounting the saddle or vertical open to air expansion tank.

    The open to air saddle tank that was above the original boiler that came with this house was a plain steel tank with a globe valve, airtrol valve, simple mesh vent plug and a sight tube and the heating water and antifreeze was a sealed system without a backflow preventer.

    The same type of tank would still pass the plumbing code requirements as an open to air expansion tank.

    The homeowner would just have to be diligent in looking at the sight glass occasionally and opening the globe valve installed before the back flow preventer to add water back into the system to replace water lost due to evaporation during the heating season.

    Knowing what I know now, I would have never let them remove that expansion tank when they put in the hand fed boiler; and I would still have it hanging there 41 years later silently doing its job of adding the water pressure of one atmosphere in 10 gallons of water to the heating loop.

    Thank you Dan.
  • Derheatmeister
    Derheatmeister Member Posts: 1,572
    edited April 2023
    Options

    I'm slightly puzzled and would like enlightenment... I have bladder tanks in service (several houses) for domestic water supply (well pump control) and I have only had one fail. It was 50 years old when it gave up (a big Well-X-Trol). What's the difference?

    How hot is the well water? Temperature is also a factor... ;)
    Solar thermal expansion tank are protected with a pre vessel for this reason.


  • Derheatmeister
    Derheatmeister Member Posts: 1,572
    Options
    Most German heating contractors use Pure Nitrogen to charge the Expansion tanks !
    They would not even think about using a compressor to fill a expansion tank and the Homeowners/Educated Customers expect them to adjust the tank with "Stickstoff"(Nitrogen)
    As some have mentioned here why do we spend 20 Bucks for ea. tire to fill them with Nitrogen yet we will not even think about using it in a expansion tank ?
    Are all the EU heating contractors wrong ?
    Why do the Nitrogen filled tanks last longer over there ?
    When we install our tanks we get rid of the precharge and install >>>Cheap<<< Nitrogen from a bottle and i must say we do not see the premature failures that many are describing here.
    Just our observations...
    SuperTech
  • Jamie Hall
    Jamie Hall Member Posts: 23,650
    Options
    Filling the tires with nitrogen is one of the most fascinating current scams I have run into. Charge 20 bucks per tire (or more) for nitrogen (which is going to cost you maybe one) when you can use your compressor for pretty much free...

    Um... right..

    Mind you now, I admire German engineering. Mostly wonderful stuff. But working on German machinery when it goes amiss is an absolute nightmare...

    On the chemical side, the small amount of oxygen in the air used for a tire or a precharge will be reacted -- to the extent it is going to -- within minutes. Tires fail for two primary reasons -- the wrong air pressure (either too low, very common, or too high -- I have seen that a few times -- or exposure to sunlight.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    DJD775WMno57
  • SuperTech
    SuperTech Member Posts: 2,205
    Options
    hot_rod said:
    hot_rod said:
    Honestly I wish we could go back to compression tanks with Airtrol fittings. No need for air vents, scoops or anything like that.  Seems like a simpler, better way to do things.
    --------------------------------------------------------------------------------------- The steel compression tanks work very well. An open to air saddle mounted expansion tank with an air-trol valve works just as well and weighs even less as it is not required to hold pressure as the tank is vented with a simple air screen vent. It is a blessing to have 5 gallons of air and 10 gallons of water below the air blanket in a compression tank for pressure control. A big thank you to the Dead Men and an even bigger thank you to Mr. Dan Holohan.
    A compression tank might be awkward on a mod con, even newer cast boilers, where would the AirTrol fitting go? You would need to add an air separator and run the vent into the tank somehow? Last I priced a tank, fittings sight glass, etc it was pushing 900 bucks for a compression tank. For what advantage?
    The advantage of not needing to replace the tank during the lifespan of the boiler.  I'm a service tech who works on a lot of boilers and replaces dozens of failed tanks every year. I don't think my customers would care about a $900 one time expense when they realized how much money they spend on bladder tank, air vent and leaky relief replacements over the years. 
    So you do offer them to your customers? How many have you installed in the last year or so?
    This is a good point.  I have installed zero unfortunately.  The cost to retrofit a boiler with a compression tank would be significantly higher than just replacing the failed bladder tank. It would be nice if compression tanks were still installed with new boilers these days but again, the cost difference.....

    The size/space difference is something I haven't considered. I guess I just like the old boilers and the way the Dead Men did things too much. 
  • leonz
    leonz Member Posts: 1,183
    edited April 2023
    Options
    The dead men did things simply making use of simple physics using hydrodynamics and temperature rise to move heat from a to z and back to a.

    An open to air saddle tank does not take up that much room at all, in fact the one that was in this house was smaller in length than the 15 gallon steel compression tank I have now.

    Diaphram tanks were an outgrowth/need of the levittown tract houses that covered all that beautiful farm land on Long Island that were built as small slab on grade kit houses with copper pipe in the floors for hot water heat.

    These homes did not have attics for open to air expansion tanks or basements for a boiler installation using gravity hot water heat or a circulator.
    SuperTechCLamb
  • hot_rod
    hot_rod Member Posts: 22,476
    Options

    Filling the tires with nitrogen is one of the most fascinating current scams I have run into. Charge 20 bucks per tire (or more) for nitrogen (which is going to cost you maybe one) when you can use your compressor for pretty much free...

    Um... right..

    Mind you now, I admire German engineering. Mostly wonderful stuff. But working on German machinery when it goes amiss is an absolute nightmare...

    On the chemical side, the small amount of oxygen in the air used for a tire or a precharge will be reacted -- to the extent it is going to -- within minutes. Tires fail for two primary reasons -- the wrong air pressure (either too low, very common, or too high -- I have seen that a few times -- or exposure to sunlight.

    Supposedly the nitrogen doesn’t leak out as fast as compressed air, 40% slower in this opinion.
    5 bucks per tire around here. Although they claim to include it when you buy 4 tires at Costco
    My truck tires run 80psi, it’s worth the extra 5 bucks to me. Or free😗
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    SuperTechDerheatmeister
  • hot_rod
    hot_rod Member Posts: 22,476
    Options
    leonz said:

    The dead men did things simply making use of simple physics using hydrodynamics and temperature rise to move heat from a to z and back to a.

    An open to air saddle tank does not take up that much room at all, in fact the one that was in this house was smaller in length than the 15 gallon steel compression tank I have now.

    Diaphram tanks were an outgrowth/need of the levittown tract houses that covered all that beautiful farm land on Long Island that were built as small slab on grade kit houses with copper pipe in the floors for hot water heat.

    These homes did not have attics for open to air expansion tanks or basements for a boiler installation using gravity hot water heat or a circulator.

    Open to atmosphere tanks allow constant O2 into the system, how could it not?
    The tank needs to be sized to handle the expansion across the temperature increase

    Closed pressurized compression tanks are a different animal. The water in those systems eventually becomes oxygen starved.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream