expansion tanks: makes, types, & reliability

[pybyr]

a "pro" in my area recently replaced the expansion tank in my parents' hydronic heating system, which (the whole system) is barely 7 years old, and had been designed and built by very meticulous people, with the whole system always regularly and carefully maintained.

the internal diaphragm on the exp. had failed and the tank had become waterlogged

the pro said that although the older expansion tanks tended to last decades, he's seeing more and more that fail within a relatively short time.

since I'm soon to be shopping for an exp tank, I'd just as soon invest in a type that's hopefully least likely to experience trouble, and most likely to last a long time.

any suggestions or observations from experience?

for that matter, any suggestions on how means and methods of sizing, installation, checking pre-charge, maintaining, etc., are likely to play into how well an exp tank works and how well it lasts?

thanks!

 

[DaveBP]

I'm with you, Trevor. Love to see a poll of the long-time pros here on their opinions of the various types and brands of expansion tanks. Those of us with pressurized storage plans are throbbing from the price of "real" expansion tanks big enough for the volume of these systems. I wonder if sizing the tanks too close to their limits and therefore making the bladder flex more back and forth makes it wear out faster. The proper X-tank for 1000 gal storage alone is about $500 or more and that's sized right to the limit of the tank acceptance.
Keeps bringing me back to earlier schemes I had of another propane tank half-filled with nitrogen for expansion. Keep a tank and regulator hooked up to add gas as it's absorbed until it is saturated and just check it once in a while after that.
Post any ideas you have or hear of elsewhere. Lot of us out here puzzling over the same issue.

 

[machinistbcb]

My oil boiler is using a 60 year old air cushion expansion tank. I have owned the house for three years and never had any problems with it.


Brian

 

[DaveBP]

Brian, just drove through Sabattus last night.
What are you using for expansion on your 1500 gal storage? How big? Is your oil boiler connected together with it or independent? By air cushion tank do you mean it does not have a bladder and you need to add air occasionally? I think they all use air to cushion the liquid expansion.

 

[machinistbcb]

Dave,

By air cushion I mean air only inside the tank, no bladder,. For my 1500 gallon tank I am using two 80 gallon air cushion expansion tanks that I was able to get from an old elementary school boiler that was being torn down. I have only had them tied in for a few months so I havent had to add air. If they start to fill up I will just drian water out which will in return add air to it. Both expansion tanks stay about 2/3 full at about 15 psi when the 1500 gallon tank is at 180 degrees.

Brian

 

[MrEd]

Why isn't it a problem to have the air in contact with the water? I thought the whole purpose of the bladder is to 1) absorb the expanded water, and 2) keep the water seperate from the air...

Is there a link to detailed info on how to build a expansion tank from a tank?

 

[pybyr]

I'm with you, Trevor. Love to see a poll of the long-time pros here on their opinions of the various types and brands of expansion tanks. Those of us with pressurized storage plans are throbbing from the price of "real" expansion tanks big enough for the volume of these systems. I wonder if sizing the tanks too close to their limits and therefore making the bladder flex more back and forth makes it wear out faster. The proper X-tank for 1000 gal storage alone is about $500 or more and that's sized right to the limit of the tank acceptance.
Keeps bringing me back to earlier schemes I had of another propane tank half-filled with nitrogen for expansion. Keep a tank and regulator hooked up to add gas as it's absorbed until it is saturated and just check it once in a while after that.
Post any ideas you have or hear of elsewhere. Lot of us out here puzzling over the same issue.

I, too, hope the many "pros" chime in here, as I, too, am wondering whether it's a case of newer installs having tanks that are shaved too close to the margin and so have to work harder, or whether some makes are just cutting corners on materials or QC.

Since I am going with unpressurized storage, I won't need one of the monstrously big & expensive expansion tanks like some of you are using (and need) for pressurized storage (I'll only need it big enough for the boiler and the unpressurized side of the piping arrangements), but I still want to "do it once and do it right" in both selecting and sizing an expansion tank so that I won't be buying a new one in a relatively short span of years

 

[Hansson]

I have the expansion tank in the top of the house.
It`s made of stainless steal.
It works very good.And if the boiler starts to make steam the steam goes out in a pipe on the roof.
(broken link removed to http://picasaweb.google.se/725hansson/Panrumsbilder#5020602465138459858)

 

[pybyr]

I have the expansion tank in the top of the house.
It`s made of stainless steal.
It works very good.And if the boiler starts to make steam the steam goes out in a pipe on the roof.
(broken link removed to http://picasaweb.google.se/725hansson/Panrumsbilder#5020602465138459858)

Thanks Hansson-- funny thing is, here in the USA, the hydronic manufacturers and installers all claim that such an installation that has an open port to the atmosphere at the top is "obsolete" and will let oxygen into the water and corrode out our boilers and any other ferrous materials in the system.

I take it your type of system is not unusual over there?

Do you do anything to test/treat the water's pH and chemical composition in order to keep the corrosion problem referred to above from cropping up?

 

[machinistbcb]

This post explains how to make your own. www.hearth.com/econtent/index.php/forums/viewthread/11559/P15/#131165

 

[Hansson]

I have the expansion tank in the top of the house.
It`s made of stainless steal.
It works very good.And if the boiler starts to make steam the steam goes out in a pipe on the roof.
(broken link removed to http://picasaweb.google.se/725hansson/Panrumsbilder#5020602465138459858)

Thanks Hansson-- funny thing is, here in the USA, the hydronic manufacturers and installers all claim that such an installation that has an open port to the atmosphere at the top is "obsolete" and will let oxygen into the water and corrode out our boilers and any other ferrous materials in the system.

I take it your type of system is not unusual over there?

Do you do anything to test/treat the water's pH and chemical composition in order to keep the corrosion problem referred to above from cropping up?

Hello
No it`s not unusual here. Noting is done to test the water.When the water is heated it becomes dead like we say here.No oxygen in it.
My system was build in 1952 and I have no problems whit corrode boilers/pipes
The original boiler from 1952 heated me to years when i bought the house year 2000.

Some guys put some sort of paraffin oil in the expansion tank.The oil floats and make a layer on the water to protect it from oxygen.

The expansion tank should be 5% of the system volume.
Here is a simple sketch how it`s put in the system
(broken link removed to http://picasaweb.google.se/725hansson/Panrumsbilder#5243928882825434866)


/Hansson

 

[BrownianHeatingTech]

Between any of the major brands, I haven't found any difference in reliability.

Quality does seem to have degraded over the last few years, but that seems to be across-the-board, not any particular manufacturer.

I suppose you could invest in a solar-rated expansion tank, as those have to be built to better standards than typical tanks, but they come with a hefty pricetag.

Joe

 

[DenaliChuck]

Hansson made an interesting suggestion.

If we were to use a propane tank as an expansion tank we could drop a couple of pounds of paraffin wax into the tank before plumbing it, minimizing air from dissolving into the water contained in the propane expansion tank.

 

[pybyr]

Hansson made an interesting suggestion.

If we were to use a propane tank as an expansion tank we could drop a couple of pounds of paraffin wax into the tank before plumbing it, minimizing air from dissolving into the water contained in the propane expansion tank.

yes- his suggestion has me thinking... if I have a hesitation it's mostly that with lots else of this system to still build, I may want to go with an off-the-shelf unit for at least one part of it.

that said, if I find the right vessel at the right price, his idea is encouraging. apparently, it's what all hydronic systems once did, 'til someone decided it was obsolete (I guess it does require manual monitoring/replenishment of water level)

 

[pybyr]

Between any of the major brands, I haven't found any difference in reliability.

Quality does seem to have degraded over the last few years, but that seems to be across-the-board, not any particular manufacturer.

I suppose you could invest in a solar-rated expansion tank, as those have to be built to better standards than typical tanks, but they come with a hefty pricetag.

Joe

does designing with some (modest) extra "headroom" in the expansion tank result in it having an easier and hopefully longer useful life? or is that not a factor

 

[DenaliChuck]

that said, if I find the right vessel at the right price, his idea is encouraging. apparently, it's what all hydronic systems once did, 'til someone decided it was obsolete (I guess it does require manual monitoring/replenishment of water level)

With the paraffin minimizing air being absorbed into the water, the monitoring/replenishment effort may be reduced to the time required to set it up for the first time. Then just periodic checks would be needed to be sure there were no changes. Hmmmmm.

 

[BrownianHeatingTech]

does designing with some (modest) extra "headroom" in the expansion tank result in it having an easier and hopefully longer useful life? or is that not a factor

I suppose it would have some, since the diaphragm would not be stretched as much, easy thermal cycle.

I think making sure that the pre-charge pressure is sufficient to keep the diaphragm collapsed when the system goes cold would have more effect, as any change in the "starting position" will directly change how far the diaphragm moves by the time it hits the hottest point in the cycle. Few installers bother to check/adjust the pressure on the tank, just "assuming" that it will be correct.

Joe

 

[pybyr]

Let's say I build my system with an expansion tank like Hansson's that is open at the top to the atmosphere, but maybe with an oil layer on top to keep oxygen out.

Let's also say, as will probably be the case in the first years of my system, that all of the "working" hydronics will be in the cellar, and that the current layout of my partially but far from fully rennovated 1830 farmhouse means that the first floor is the only place that I am likely to be able to "fit" an "open" expansion tank in a place that is not subject to likely freezing.

I know that the open expansion tanks basically depend on the weight of the water to create and maintain pressure in the hydronic system--

will an "open" type tank that's less than 8 ft) (and probably more than 3-5) above the top of the boiler create enough gravitational "
"head" in my Econoburn's system to maintain enough pressure to minimize risks of flasbhing to steam in some pocket of the boiler/ piping?

Thanks

 

[BrownianHeatingTech]

will an "open" type tank that's less than 8 ft) (and probably more than 3-5) above the top of the boiler create enough gravitational "
"head" in my Econoburn's system to maintain enough pressure to minimize risks of flasbhing to steam in some pocket of the boiler/ piping?

Water adds 0.433psi per foot of water column. So, to create a pressure of 10psi, you'd need a 23-foot column of water.

Joe

 

[pybyr]

will an "open" type tank that's less than 8 ft) (and probably more than 3-5) above the top of the boiler create enough gravitational "
"head" in my Econoburn's system to maintain enough pressure to minimize risks of flasbhing to steam in some pocket of the boiler/ piping?

Water adds 0.433psi per foot of water column. So, to create a pressure of 10psi, you'd need a 23-foot column of water.

Joe

thanks Joe- but I guess I wasn't that clear on my question-- is there some minimum pressure beneath which I should not design or run my system?

I think I recall reading in my borrowed but since returned copy of Siegenthalers's Modern Hydronic Heating 2nd Edition that the lower the pressure, the less oxygen the water will retain--

-- which makes very low/ modest system pressures seem good at first glance--

but then I also realize that higher pressures will raise the boiling point of the water, which seems like it'd be a good safeguard against sudden formation of steam (with resulting surges of pressure) in some localized "hot spot" within the boiler or other part of the system

 

[pybyr]

decided to go straight to the source, and called Econoburn's tech line. Dale answered, and like everyone else I've dealt with at that company, was ready, willing and able to share knowledge and help

he strongly advised against any sort of system that's open to the atmosphere, even indirectly, and even with an oil layer to theoretically keep the air from exposure to the water in an exp. tank. He said that beyond the 02, there were other reasons (dust, bacteria, etc) that basically meant that an open system would need a degree of start-up and ongoing treatment and monitoring that were very worth avoiding.

obviously, based on Hansson's track record, the semi-open pressurized systems _can_ work OK under some conditions, but it sounds like a trade-off that in my case I think I'll avoid

Thought I'd share that end answer, and thanks for all the other suggestions.

 

[Hansson]

He said that beyond the 02, there were other reasons (dust, bacteria, etc) that basically meant that an open system would need a degree of start-up and ongoing treatment and monitoring that were very worth avoiding.

obviously, based on Hansson's track record, the semi-open pressurized systems _can_ work OK under some conditions, but it sounds like a trade-off that in my case I think I'll avoid

Thought I'd share that end answer, and thanks for all the other suggestions.

I think he is afraid of something he don't now anything of..

Dust? And bacteria? I really wonder how he is thinking.

 

[BrownianHeatingTech]

thanks Joe- but I guess I wasn't that clear on my question-- is there some minimum pressure beneath which I should not design or run my system?

Personally, I wouldn't set it up for less than 10psi.

Joe