She canna take any more, Cap'n! She's gonna blow!
Comments
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Yes that is a good starting point, and that is how I initially charged the system this heating season. Someone made a comment about the 8 gallons but it wasn't me.
There are no fittings for a sight glass on this tank.
It seems to be that the bottom line is whether or not 12 gallons of air at 12 psig is sufficient for the volume of water in the system, given that I added radiators. If it was sized correctly before I added radiators, perhaps the 24 gallon tank is a bit too small.
The only real difference this season is that the setpoint of the boiler is sometimes higher (due to the ODR boost mode) than it was in previous years, which adds to the problem. I would like to avoid replacing the tank, which leads me to these options:
- reduce the water in the tank to say 8 gallons at 12 psig - (but would that affect the proper operation of the Airtrol?
- reduce the max setpoint to say 160, or turn off the "boost mode", or both - so on cold days it would take longer to heat the house.
Make sense?
—Eric0 -
Why would you want more than like 5% or 10% water in the tank with the system at room temp and the air at the cold fill pressure? The only reason i can see that you want any water is if the system gets even colder there will be enough water in the tank to keep the air from leaving the tank and that is not going to be much between 70f and 30f.
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Connections don't scare plumbers :) they make tight connections for a living. Gas, liquid, pressure, vacuum, etc
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
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The problem with reducing the initial water volume is, as you note, @EricPeterson , it would affect the operation of the Airtrol — which would, eventually, try to bring the water volume up to 12 gallons or so cold anyway. In time, it would succeed… it has a way of doing that!
However, on whether the tank volume is adequate or not — as in so many things, the best guide is the simplest: what, assuming the tank was properly set initially, does the gauge pressure rise to at various temperatures? If the gauge pressure stays below 25 psig at your highest set point temperature — that boost temperature — then you're fine. It would be nice, I'll agree, if it were lower, but… it doesn't have to be.
Now if the pressure rises too much, then yes you would need a bigger tank. An Extrol EX-90 — the biggest in the Extrol EX line — is, however, roughly equivalent to your existing compression tank, and so it wouldn't be big enough either. You might have to go up to the SX-90V.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England0 -
More that once on this list we have seen undersized tanks on converted gravity or large piping systems. It is tough to guesstimate the total volume with piping that is not visible, and calculating radiators.
I prefer the diaphragm or bladder type expansion tanks to eliminate all the issues you have and they are less $$ even if you have to stack multiple tanks.
The tank with the most expansion capacity will always be the full acceptance type bladder tank, as most all or the tanks capacity is available.
With a diaphragm type, only about 65% is useable expansion space.
Use the steps above to get the tank to "square 1" then monitor pressure increase. The tank you have may be fine.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
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Start with 0 gallons of water, then use the water pressure in the boiler to compress the air in the tank is my recommendation. (illustration on the right)
Your procedure indicates that you start with 12 gallons of water at 0.0 PSI then use the boiler water to compress the air (illustration on the left)
I am telling you that you should start with no water and 24 gallons of air space at 0.0 PSI in the tank. Then there will be more air to compress. There will be more air space in the tank at 12 PSI
BOTTOM LINE to ADD MORE AIR!!!
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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To be clear, my procedure was to isolate the tank, start with 12 gallons of water, pressurize the remaining 12 gallons of air in the tank to 12 psig, then open the valve to the system piping.
If I understand you correctly, you are suggesting that I isolate the tank, drain it. then open it back to the system.
- With the boiler off and cold, close valve to compression tank,
- Drain tank
- Open valve to compression tank.
Do I have that right?
When we get some warm days, I will check the tank to see how much water is in there now, then do a couple of experiments related to filling and pressurizing the tank.
—Eric
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It's worth considering. If I do elect to go with an expansion tank, any idea what would be the proper capacity as a step up from a 24 gallon compression tank? Something a bit more than 12 gallons?
—Eric
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You need to know the volume of water the whole system holds, the delta t from ambient to setpoint and the desired cold and hot pressures. From there Amtrol has a formula to calculate the tank size.
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Yep.
Trying to squeeze the best out of a Weil-McLain JB-5 running a 1912 1 pipe system.0 -
Great heavens. Am I writing in Greek?
There are two ways to get that compression tank set up correctly.
One. Empty tank completely. Close all drains and vents on the tank. Connect tank to system. Pressurize system to 12 psig. You now have about 12 gallons of water in the tank and 12 gallons of air, pressurized to 12 psig.
Two. Fill tank with 12 gallons of water (Airtrol 50% setting). Close all valves, drains, and vents. Pressurize tank with suitable air compressor and Schrader type valve to 12 psig. Adjust system pressure to 12 psig. Connect tank to system. You now have about 12 gallons of water in the tank and 12 gallons of air, pressurized to 12 psig.
Now on the expansion tank, if you want to go that way. You will need to estimate the water volume in the entire system and use one of the handy dandy calculators to get the required tank size. I agree with @EdTheHeaterMan that a full acceptance bladder tank is a much better type. I will note that if you 24 gallon compression tank, set up as above, isn't big enough you will need more than 12 gallons acceptance volume in the expansion tank, which gets you into either two residential type EX series tanks or the larger SX series tanks.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England0 -
How are you charging the tank to 12 PSI with 12 gallons of water in it? Are you adding compressed air some how? Most homeowners and professionals do not add compressed air to a compression type expansion tank like yours.
If you are adding compressed air, then that works too. But you need to be sure you don't add too much air pressure. (But I see that you have more than the one gauge that comes with the boiler)
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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Greek? No, I understand completely what you are saying @Jamie Hall and agree with it.
And @EdTheHeaterMan yes I have multiple gauges and am careful about watching the pressure.
There was that one time when I forgot and left the fill valve in fast fill mode, but I won't do that again.Thanks all for the useful insight and information. I will do some testing and figure out what to do next.
—Eric
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This is the easiest way to run some options. This uses Critical Sizing Method. Some other calculaters just ask for BTU size of boiler, and max. temperature, so not accurate for systems like yours.
I guessed 100 gallons system volume 55° fill water at 17 psi fill pressure.
Generally 27psi is the default on these sizer programs for the highest pressure on 30lb relief valve systems.
Notice that a pre-charge expansion tank is usually 1/2 the size of a compression tank.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
let's come back to what Ed defined on pg1, "drain the tank", but you should open up that second port on the filtrol, or somewhere there, to let air into the tank as it drains, otherwise it's a straw with a finger on the top end holding back water,
Are you sure you had all the water out when draining prior?
known to beat dead horses
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Good question. But yes all the water was out. The drain at the bottom of the tank is a 1/2" fitting so it drains well. Could also take out the Airtrol assembly if you wanted.
—Eric
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airtrol, right, I wouldn't take it off, but loosen that small nipple to be sure you let air in
known to beat dead horses0 -
then when the draining is done, close airtrol nipple, drain valve, and reopen to system, as above , , ,
known to beat dead horses0 -
yep that’s the way I’ve done it.
—Eric
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@eric @EricPeterson said: "Good question. But yes all the water was out. The drain at the bottom of the tank is a 1/2" fitting so it drains well. Could also take out the Airtrol assembly if you wanted.
—Eric"
Here is the reason you don't want to remove the AirTrol® Fitting
Go to time stamp 35:40 and watch until 37:15 for the first mention of Henry's Law. Then fast forward to @2:14:20 and see the full explanation and why the AirTrol® fitting needs to be there. That explanation stops at around 2:17:42
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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Oh I didn't mean remove it permanently, I meant for the purpose of helping to drain the tank. But not necessary. The Airtrol combined with an IAS does a great job of keeping the air out of my system.
—Eric
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You could also use one one of your radiators as an expansion tank. After partially or totally draining the system, fill it back up and don't bleed air out of a radiator that either overheats or in a room that's not used much.
I have very few original ideas. Mr. Dan Holohan gave me that one.
8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour
Two btu per sq ft for degree difference for a slab1 -
Ha! I had the same thought as there are a couple of radiators that are good candidates for such a purpose. Maybe it was a sub-conscious memory from having read Dan's books years ago when I first stumbled upon The Wall.
Only downside I think is that a future homeowner might unknowingly bleed the air out of that radiator and then they're back to square one.
—Eric
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If the radiator is the PONPC, then the pump would want to move there.
If the pump is at the boiler and the uppermost radiator is the PONPC, you are pumping at the PONPC.
I'm not sure what the pressure profile would look like if you have a tank at the boiler and some radiators are also expansion devices?
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
I do not know how to answer that question.
I did this today:
- took some measurements of temp & pressure when the boiler was running early in the morning.
- watched the number rise steadily for over an hour.
- observed that the boiler maxed out around 35 psi when it was cycling on and off the max setpoint (170).
Once the system cooled down:
- using the Aitrtrol, drained the excess water from the compression tank, it was 3-1/2 quarts, not exactly water-logged but almost a gallon. This left the 24 gallon tank half full with water.
- pressurized the tank so that the system gauge was reading 10 psi (using a bicycle pump).
- turned off the water feed temporarily (so pressure would remain stable).
I also verified there was no air in the system by checking the top floor radiators.
So tomorrow I will take some more measurements and see if this mitigates the problem sufficiently.—Eric
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I'm almost wondering, @EricPeterson , if there is any other air removal device anywhere on that system of yours. Once the compression tank is adjusted — as you have done — it really shouldn't lose air for a long time (like months). But all it would take is one other air removal device — microbubble separator or anything like that…
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England0 -
at 10psig it could potentially suck air in at the top emitters if there is something like a packing that is watertight but not airtight
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but Jamie— even if there were an air separator, it’s not like there is any water flowing from the tank over to it.
It would still take quite some time for the air to diffuse into the water, through that stagnant water through the pipe all the way to the air separator, no?
NJ Steam Homeowner.
Free NJ and remote steam advice: https://heatinghelp.com/find-a-contractor/detail/new-jersey-steam-help/
See my sight glass boiler videos: https://bit.ly/3sZW1el1 -
Adding fresh water adds air dissolved in that water, you want that to find its way to the tank rather than be vented.
Without the airtrol fitting, which is just a u bend of sorts to reduce gravity flow, hot water from the boiler will rise in to the tank and cold water in the tank which holds more dissolved air, will fall out of the tank and get heated in the system and release some of its dissolved air. The airtrol fitting slows this but doesn't eliminate it so over time some of the air would find its way to an air eliminator. This is why the air separator should be connected to the compression tank in a compression tank system.
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that water isn't stagnant though, as the system heats and expands it flows into the tank, then as it cools, the tank pressure flows back to the system, the airtrol fitting sorts the lower water, which is less air entrained, back to the system, if there are other air vents than the tank, the entrained air finds those vents, and or settles into rads,
I don't think the tank is ever getting to empty, a couple quarts isn't 12 gallons, completely empty the tank by letting air in thru the airtrol, then seal it up and return it to system pressure,
you can google this thru BnG since you're not listening to us here
known to beat dead horses0 -
You might be surprised how fast that can happen…
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England0 -
I'm listening to all of this, not sure where that comment came from. I have piped the air elimination exactly as B&G specifies with the IAS (Internal Air Separator) piped to the Airtrol on the compression tank. And I have stated this before in a different post "In Praise Of Airtrol" - because this setup has eliminated the air accumulation at the top of the system the plagued me for years.
Believe me when I say there are no other air elimination devices installed. Zip, nada, zilch. The boiler does not have one, and I did all the near-boiler piping and it's just black iron pipe and fittings, zone valves, ball valves, and a Caleffi thermostatic valve.
I simply don't see any difference between emptying the tank completely then filling it back half-full with fresh water, and doing what I did which was to simply reduce the water level to half-full. And I don't see any difference between pressurizing a half-full tank by hand versus using water into an empty tank to pressurize. At least this way I am starting from a known state: 12 gallons of water, 10 psi. Either way you end up with 12 gallons of water and 12 gallons of air at a certain psi.
Yes the psi is not 18 as it should be. But for operational purposes, with the system filled with water, I don't see that it's needed. The circulator is moving water through the system just fine. And this is just temporary to see if the pressure will now stay below 30 with a setpoint of 170 and the correct amount of air in the compression tank.
Probably the root cause is that with the additional piping and radiators added over the original installation, I have exceeded the capacity of the compression tank. That is my working theory right now anyway. This problem has only been exposed because I a) eliminated the air in the system, which in the past was allowing some extra room for water to expand, and b) I am hitting a higher setpoint of 170 than I was in the past. So one easy solution might be to simply reduce that setpoint to say 165. That might well work even with a cold PSI of 18.
—Eric
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do tell, you tease 😅
NJ Steam Homeowner.
Free NJ and remote steam advice: https://heatinghelp.com/find-a-contractor/detail/new-jersey-steam-help/
See my sight glass boiler videos: https://bit.ly/3sZW1el1 -
I suspect your working theory is correct, @EricPeterson . Just wanting to be sure you've covered all the other possibilities — which it seems you have.
And there is nothing wrong with setting up a compression tank as you are doing — although I think it's harder than it needs to be…!
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
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At this point I just want to see if I can make the existing compression tank work! Replacing it with expansion tanks(s) would take some re-piping. If I need to I will. Or there are 30 gallon compression tanks. $$$$.
I do appreciate all the comments and questions. I really do.
Thank you all.—Eric
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Situation improved with:
- static pressure of 10 psi
- removal of excess water from compression tank
Today the pressure maxed out at 26 at the setpoint of 170. That's a relief (no pun intended). I think the next thing I will try is to lower the max setpoint to 165, raise the static pressure, and see where I end up.
Long term I may have to consider increasing the air capacity. Per Xylem you can add additional compression tanks so that is probably the way I will go. The smallest one is 15 gallons which should be enough. That one also uses an ATF-12 Airtrol. I know, I know that everyone uses expansion tanks now. But I like the simplicity of the compression tank. My boiler is already set up for this. And Xylem still sells them, right?
—Eric
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A compression tank system is considered an "air management" type of system. So you or some device needs to size and manage the air bubble. As you have learned it is not always as easy as it sounds.
Any hydro pneumatic type of expansion vessel is an air removal system. You can have, and do want efficient air removal devices with these tanks.
In either case make sure you have about 5 psi positive pressure at the highest point in the system.
High point X .433 then add 3-5 psi to that. Without adequate fill pressure you could trap an air pocket and have circulation issues.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream1 -
The Airtrol is the air removal system…
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England0 -
The terms the industry uses, Air Management, Air Removal. This manual does a good job of explaining the systems.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
Until recently, we had a 40 gallon plain steel compression tank serving two 100+ gallon systems with two WGO-5 boilers. I also installed an Airtrol ATF-12 a year or two ago thanks to the knowledge of the good people on this site.
The 40-gallon tank was big enough that I could set our static pressure to 18 psi (just for plenty of margin in a 2-story house) and not have the hot pressure exceed 22 psi or so.
But since we may soon need new boilers and I didn't have confidence in my fellow condo owners to be able to manage the compression tank and Airtrol in future, I reluctantly joined the "modern" age and recently took out the steel compression tank and installed an oversized SX-40V diaphragm tank. The SX-40V has been doing well, with only 4-5 psi pressure gains when both boilers are hot. I have static set at 15, and the hot pressure never exceeds 20. Air elimination is now done by Caleffi Minicals piped into the integral air separator ports on the boilers. Eventually when the boilers are replaced, we'll upgrade to micro-bubble air separators on the supplies.
So if you are going to add a tank anyway, you might want to consider going "whole hog" and just piping in something like an SX-40V (you should do your own sizing first, obviously). Using the Supply House online calculator, it recommended an SX-30V, but I went one size up to buy a little extra margin, and I'm happy I did, as the price difference is minimal.
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