Diaphragm expansion tank piping

jesmed1

Thank you all for your expert thoughts on my ongoing tribulations with the two WGO-5 hot water boilers in our 4-unit condo building. We've decided as a condo association to wait until one boiler conks out before making any major modifications to the piping.

However, I would like to solve our ongoing air entrapment problems, or at least improve the situation somewhat. We have a 40-gallon steel compression tank in the ceiling above the boilers, and every year the boiler tech drains it and refills it. In the process, more dissolved air makes its way into the system, where it bubbles out into the radiators and is difficult to expel from some of the radiators.

So my question is, can I replace the old expansion tank with a new diaphragm tank, piped as shown below? I know this is not the *best* way to pipe it (with circulators pumping away, and with new air eliminators on the supply), but I don't have the option of *best* piping right now. I only have the option of adding it to the piping that we have, with a minimum of rework. As shown in the diagram, I could plumb this myself off the existing 1/2" copper.

So as shown, it would go on the floor next to one of the boilers, using the same 1/2" copper pipe that now goes to the compression tank in the ceiling.

And my question is, would this at least be *better* than what we now have, in terms of reducing air entrapment problems in the radiators? I know it is not the *best* way to do it, but as I said, I don't have the option of doing it the *best* way. I just want a *better* way that's good enough, until in a few years a boiler fails and then we can repipe everything the *best* way.

EBEBRATT-Ed

Yes that will work fine. I would suggest an isolation valve on the expansion tank pipe and a drain valve between the isolation valve and the ex tank.

jesmed1

EBEBRATT-Ed said:

Yes that will work fine. I would suggest an isolation valve on the expansion tank pipe and a drain valve between the isolation valve and the ex tank.

OK, thanks Ed. Based on our approx 300 gallon total water content, and max 140 degree water, I figure an expansion ratio of 0.02 is adequate, for a 6 gallon tank acceptance. The SX-30V accepts up to 11 gallons. Most of the time we'll be closer to 3 gallons acceptance, as both boilers rarely run at the same time. So I think we have good margin there.

Jamie Hall

Well, yes that will work. But... it might make some sense to figure out how air is getting into the system in the first place, and why the connection to the compression tank in the ceiling isn't getting rid of it. Since if you don't, you will still have air in the system... The comment that the compression tank has to be drained tells me that the arrangement allowing it to trap any air in the system isn't working.

jesmed1

Jamie Hall said:

Well, yes that will work. But... it might make some sense to figure out how air is getting into the system in the first place, and why the connection to the compression tank in the ceiling isn't getting rid of it. Since if you don't, you will still have air in the system... The comment that the compression tank has to be drained tells me that the arrangement allowing it to trap any air in the system isn't working.

Thanks, Jamie. I've been assuming that the only reason air gets in is that the boiler tech drains the expansion tank as a matter of course every year. I've never seen them bother to check whether it's waterlogged or not. I don't believe it is. They just go ahead and drain and refill, and the dissolved air in the new water then bubbles out into the system. Or so I thought.

As for why the existing tank doesn't trap the air, I think it's because the tank isn't teed off the supply pipe. These boilers have separate ports for makeup water apart from the supply connection, and the makeup water and expansion tank are piped into that separate port. So there's virtually no water flow through that part of the system. All the water is flowing out the 1-1/4" supply pipe, and back through a return pipe of the same dimension. Meanwhile, the water in the make-up water/expansion tank piping is separate from that main flow, and thus doesn't collect any bubbles unless they happen to bubble up from inside the boiler up to that separate pipe fitting. (I don't know what the inside of the boiler looks like).

So maybe I'm wrong, but I've always assumed that the air was being introduced by the boiler tech draining and filling the tank each year (whether or not it's needed). And since our piping arrangement doesn't seem optimized to direct air bubbles into the expansion tank, the air just circulates through the supply and ends up in the radiators.

But if that assumption is wrong, then as you say, a diaphragm tank won't solve the problem. I just don't have any other reasonable hypothesis as to where else the air might be coming from.

Gilmorrie

I would stay with the old compression tank - and just quit draining it on a regular basis - or ever, unless the tank becomes waterlogged. If you do this, and the tank doesn't become water logged, then what's not to like?

Remove any air removal devices on your system. They will deplete the air in the tank and it will become waterlogged for sure. Air removal devices should only be used with a diaphragm-type tank.

That old tank has been there and presumably working satisfactorily for decades. Your service person may be unfamiliar with it?

leonz

If that galvanized pipe that is mated with the copper pipe is
connected to a tapping in the compression tank that's a problem.

They don't label it but that is an airtrol fitting in the other tapping
of the tank in the drawing with the riser pipe coming from the boiler.

The way your tank is plumbed the hot water and cold water cannot
pass to return to the heating system because the airtrol valve is not
in the bottom of the tank.

Page 5 of the B+G airtrol manual shows you how the drain o tank and
Airtrol valve should be plumbed if used together.

jesmed1

leonz said:

If that galvanized pipe that is mated with the copper pipe is
connected to a tapping in the expansion tank that's a problem.

It's not connected to the tank.

leonz said:

They don't label it but that is an airtrol fitting in the other tapping
of the tank in the drawing with the riser pipe coming from the boiler.

OK, I see what you mean. We don't have an "Airtrol" trademark valve there, but there is a fitting with a bleed screw.

leonz said:

The way your tank is plumbed the hot water and cold water cannot
pass to return to the heating system because the airtrol valve is not
in the bottom of the tank

See my comment above. Below is a pic of the fitting at the other end of the tank. It has an air inlet bleed screw to admit air when the drain valve at the other end of the tank was opened. I don't know if it has any "airtrol"-type tubes inside. We could replace it with a real airtrol if that would help.

jesmed1

Gilmorrie said:

I would stay with the old compression tank - and just quit draining it on a regular basis - or ever, unless the tank becomes waterlogged. If you do this, and the tank doesn't become water logged, then what's not to like?

Remove any air removal devices on your system. They will deplete the air in the tank and it will become waterlogged for sure. Air removal devices should only be used with a diaphragm-type tank.

That old tank has been there and presumably working satisfactorily for decades. Your service person may be unfamiliar with it?

The old tank has indeed been there for decades. But I've lived here for ten years, and when I got here, the heating system was full of air because none of the owners knew they needed to bleed the radiators, and the boiler techs had been draining and refilling the tank annually whether it needed it or not.

So it's been a combination of ignorance on the part of the condo owners, the boiler techs, and on my part as well, since I'm still learning.

We don't have any air removal devices, so that's not a problem. So maybe the solution is just to tell the boiler techs to stop draining the tank every year? I had assumed that, if they were doing something, there was a good reason for it, but evidently not. I'm 99% sure the tank never gets waterlogged, as it's massively oversized at 40 gallons, and the relief valves never pop.

leonz

Hello jesmed1,

Your system is easy enough to fix, and do it right so it never gives you any problems.

All your group needs to do is hire a licensed plumber that is familiar with how a steel compression tank system works-I had one plumber tell me all my heating problems were because of my steel compression tank of which I knew better and he did not.

Follow the B+G literature diagram on page 4 page for the proper installation for your system add an ATF-12 Airtrol Valve, the needed pipe and fittings to tie into your boiler and keep the service people away from that tank and tell them to just service the oil burner, clean the boiler combustion chamber, change the oil filter, do thier combustion analysis and keep thier hands off the drain valve period.

You probably need to add a low water cut off switch too so keep that in mind when talking to your plumber to bring the boiler up to code as well.

I am not trying to spend your collective moneys I just want you to have good heat as your massive number of radiators will do that for all of you once you have the boiler plumbing fixed.

I would strongly encourage you to order 2 of Mr. Holohans excellent books from the Heating Help Bookstore.

These fine books are "CLASSIC HYDRONICS" and "PUMPING AWAY".

Classic Hydronics is a wire bound paperback printed on heavy paper with it being wire bound it will let you
fold it under itself and lay the book down and read it while you are looking at your boiler to better understand how it works.

You can order them with a debit or credit card through the web page and it eliminates the middleman-amazon and receive them in a few days.

It may be worth the time to add the extra plumbing for a second boiler and have it piped correctly and have it ready to connect it to a second boiler when its needed so that is worth the time for a meeting with the other tenants.

jesmed1

Thank you, Leon. I have Classic Hydronics and will look for Pumping Away. I'll also look into getting the Airtrol ATF-12. Thanks for your help.

EBEBRATT-Ed

@jesmed1

I will run contrary to some of the above posts. That's nothing new.

I say install the bladder tank. Once that is done you can add automatic air vents (I would put a petcock under them) on any troublesome radiator

Its pretty normal for a compression tank to waterlog over time.. When hot water migrates to the compression tank it cools and absorbs air. It migrates back into the system and gets trapped in the radiation. In your case being a gravity system, the pipe is oversized for the flow. Air gets trapped in the radiation and cant get out and can't get pulled back to the boiler or to any air removal device because of the low velocity.

jesmed1

EBEBRATT-Ed said:

@jesmed1

I will run contrary to some of the above posts. That's nothing new.

I say install the bladder tank. Once that is done you can add automatic air vents (I would put a petcock under them) on any troublesome radiator

Thanks, Ed. I will probably go ahead with the diaphragm tank as you say.

While I appreciate the pointers from leonz and others on making the existing compression tank work, the problem remains that future condo owners here are not going to have the knowledge to keep the old steel expansion tank working optimally. Even our boiler techs apparently don't fully understand their workings. And, air can still migrate into the water in the expansion tank, even if it doesn't waterlog.

So adding the diaphragm tank is, at this point, the easiest upgrade we can make, since it doesn't involve breaking into any of the piping except the 1/2" copper to the existing tank. Then after the diaphragm tank, we can add automatic air vents as you say.