Setting proper level in expansion tank

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Old 10-18-10, 09:30 AM
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Setting proper level in expansion tank

I am getting ready to replace the bearing assembly on one of my circulation pumps and while the system is drained I wanted to address my full expansion tank (baffle-less type). I have a Bell and Gossett ATF12 Airtrol fitting in the bottom of the tank and want to know if when the system drained or when the valve between the air separator and the ATF fitting is closed, can I just open up the manual vent of the bottom of the fitting to set the expansion tank water to the correct level (when water stops running out of valve the water in the tank is at the correct level(?))? Or do I have to unscrew the plug at the bottom of the tank to let the water out and open up the manual valve on the ATF12 to let air in?

There are instructions on the B&G website for setting up a new tank, but I didn't see anything about adjusting the water level in an existing tank.


TIA,
BWSwede
 
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Old 10-18-10, 10:54 AM
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You need to vent the tank. Best to remove the plug on the tank and install a hose bib in its place.

The small plug on the Airtrol tank fitting is connected to a tube extending into the tank. That will help break the vacuum, but a hose bib on the tank will allow you to drain the tank completely.

Once you've got the tank completely drained, shut the small plug, and fill the system. The water level in the tank should wind up where it needs to be, but you can crack open the plug to check the level.
 
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Old 10-18-10, 11:25 AM
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Not sure if this is something you've considered, but if you are going to all this trouble, and draining the system anyway, have you considered just putting in a modern, diaphragm-type expansion tank (Extrol)? They aren't that expensive, and will cause far fewer problems in the long run...
 
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Old 10-18-10, 12:12 PM
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Originally Posted by jgalak View Post
if you are going to all this trouble, and draining the system anyway, have you considered just putting in a modern, diaphragm-type expansion tank (Extrol)? They aren't that expensive, and will cause far fewer problems in the long run...
My 60-year-old conventional steel tank has caused no problems. Bladder tanks lose air slowly but continuously (just like bicycle tires), requiring the water side to be drained every couple of years to pump them up - and eventually, the bladder fails altogether. And there is no way to check the level like can be done with a conventional tank equipped with a B&G Airtrol tank fitting. A conventional tank, properly installed, retains its air cushion indefinitely - and the cushion is replenished whenever air finds its way into the system, during maintenance for example.

Yes, bladder-type tanks are cheaper - which is one reason they are used.
 

Last edited by Mike Speed 30; 10-18-10 at 12:28 PM.
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Old 10-18-10, 12:23 PM
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By the way, Swede, you're draining the tank because you think it is full? With an Airtrol tank fitting, an Airtrol boiler fitting, and the pipe between the two sloped upward, the air cushion will last indefinitely. You don't have an air elimination device on your system do you - about the size of a tomato-paste can with a vent valve on top? Those are for bladder-type tanks only.
 

Last edited by Mike Speed 30; 10-18-10 at 02:26 PM.
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Old 10-18-10, 12:27 PM
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Yes, cheaper... also lighter and smaller. All these things make them more attractive all the way from the factory, to the stocking warehouse, through the installer, to the end user.

And I think that it has become a common misconception that the reason they have been almost universally preferred these days is because they are more reliable. They aren't. In fact, maybe less reliable... but the fact that they are cheaper, lighter, and smaller offsets that fact.

In a well designed and maintained system with a steel tank properly installed, one might never in their lifetime have to do anything to the tank. Try getting that out of a bladder tank!
 
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Old 10-18-10, 12:52 PM
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Well, I certainly don't have the experience of some of the other posters here, and so I may be wrong.

My comments had to do with the fact that 1) I've heard many, many stories of dealing with a waterlogged conventional tank, and 2) several of the components I'm currently installing in my system (don't recall which ones off hand, I think it's the TT boiler and the Wilo Eco circulator) specify the use of diaphragm tanks only.
 
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Old 10-18-10, 02:48 PM
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Originally Posted by jgalak View Post
I've heard many, many stories of dealing with a waterlogged conventional tank, and 2) several of the components I'm currently installing in my system (don't recall which ones off hand, I think it's the TT boiler and the Wilo Eco circulator) specify the use of diaphragm tanks only.
If you can refer us to the prohibitions against the use of conventional steel tanks, that would be interesting. I haven't heard that before - wonder why that would be?

I haven't been keeping statistics, but it seems like most of the expansion tanks, discussed on this forum, that have lost their air cushion are bladder types. I'll stick my neck out here: a properly installed conventional tank should NEVER lose its air cushion. Where would the air go? Maybe back into the circulating water? It would then wind back up in the tank - assuming there are no automatic air eliminators on the system.
 
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Old 10-18-10, 02:49 PM
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Thank you all for your thoughts and recommendations. Since the expansion tank has lasted 60 years so far I think I'll stay with it.

The only reason I see that this happened (correct me if I am wrong) is that the last time I had a boiler company take a look at my relays to tell me what was wrong at the time, the technician must have opened up the city water valve right before my autofill valve. I didn't know he did this. I always keep that valve closed in case I spring a leak somewhere when I am not home. That move by the technician along with the fact that I have an air elimination device up at the highest point of piping in the attic I believe caused my expansion tank to fill up.

I think that when I drain my system to replace the bearing assembly on one of my pumps that I will also drain my expansion tank. To make things easier for me in the future I plan on putting an isolation valve between my air separator device and the expansion tank as well as a hose bibb under by expansion tank.

I am a little nervous about doing the work but taking it one step at a time I should be OK.

Thanks again for all the advice. I am all ears for any other words of wisdom sent my way. I really appreciate it.

BWSwede
 
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Old 10-18-10, 03:12 PM
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Originally Posted by BWSwede View Post
the fact that I have an air elimination device up at the highest point of piping in the attic I believe caused my expansion tank to fill up.
An air eliminator combined with a conventional expansion tank is a big no-no, and undoubtedly accounted for your tank problem. The same thing will certainly happen again, probably on Christmas day when all the hardware stores are closed, so you might as well fix it now.

I wouldn't put an isolation valve ahead of the air eliminator. I would get rid of the air eliminator altogether. If you want to be able to bleed air from that high point in the attic (after, say, refilling the system), replace the air eliminator with a small ball valve or globe valve. Does your air eliminator have a vent cap? For the time being, screw it down tight to gag it.

You problem wasn't caused by the plumber who opened the shut-off valve ahead of the pressure reducing valve.
 
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Old 10-18-10, 04:39 PM
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In a well designed and maintained system with a steel tank properly installed
That's the key right there... WELL DESIGNED and MAINTAINED, PROPERLY INSTALLED.

If a system is thrown together willy-nilly by Bozo and ClaraBelle, of course you will have problems. Those problems won't be only with the expansion tank, but it's often one of the first defects that show up... and usually in a remarkable way, with the relief valve opening... and people remember remarkable stuff. That's one reason you hear 'so many stories'.

A 'system' needs to be ENGINEERED. In other words, designed by someone with the qualifications required to understand WHY they are doing what they are doing.

Sure, Bozo, ClaraBelle and perhaps even the Munchkins can throw a system in and it will 'work'. But it certainly won't be problem free.

Steel compression tanks shouldn't be simply tee'd of any old pipe. They need to be piped to the TOP of a suitable air separator that is placed in the proper location in the system such that it can catch any passing air and vent it BACK to the tank from whence it came.

I would venture to say that of all the system pics that have been posted here, I can't recall seeing ONE that was piped off the top of an appropriate air separator.

The system piping needs to be designed with proper flow so as to keep the air moving through the pipes rather than allowing it to 'pocket'.

When this happens, Bozo comes out and charges some poor homeowner some exorbitant fee to install an air bleeder... and this is where the problems start... you can NOT have automatic air bleeders on a system with a conventional tank. The air will be vented, only to be replaced by water from the automatic fill valve. Repeat this cycle enough times and guess what becomes waterlogged? No wonder!

Enough ranting on this I think...

Would I design a modern system with a steel compression tank?

No. Bladder tanks are cheaper, smaller and lighter, and IF PROPERLY MAINTAINED can last a damn long time. (the Extrol 30 on my own system is 25 years old... believe it or not...) That maintenance MUST include isolating the tank from the system and checking the air charge AT LEAST every 2 years, and yearly is even better.

I believe the failure mode for MOST bladder tanks is that they are NEVER checked for proper air charge. What happens then is that the bladder is allowed to flex way beyond it's design specs... and it fails.

But we've really strayed from Swede's original post, haven't we?
So, back to our regularly scheduled programming...
 
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Old 10-18-10, 04:42 PM
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You problem wasn't caused by the plumber who opened the shut-off valve ahead of the pressure reducing valve.
Maybe... maybe not?

What if the reducing valve had a small leak and over pressurized the system? That would certainly account for the relief valve opening.

No, maybe not the waterlogged tank...
 
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Old 10-18-10, 04:48 PM
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BW, you said:

my air separator device and the expansion tank
Your tank is piped off the top of an air separator? Kudos to the installer. Even more kudos if (as Mike mentioned earlier) the piping is all sloping upward toward the tank, and even more if the piping is at least 3/4".
 
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Old 10-18-10, 05:30 PM
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Great information guys and very fascinating discussion.

A couple of clarifications and questions:

An air eliminator combined with a conventional expansion tank is a big no-no, and undoubtedly accounted for your tank problem.
I learned this from questions I asked to the forum last year. The air eliminator is not original to the system from what I can tell. It looks like more of a modern era device compared to all the all the other fittings and valves. I wish it was never installed.

I wouldn't put an isolation valve ahead of the air eliminator.
I wasn't planning to. I am planning on putting an isolation valve after the air separator but before the Airtrol fitting. So when this happens again, if it does, before I can get rid of the air eliminator in the attic, I can just drain the tank without draining the entire system.

Does your air eliminator have a vent cap? For the time being, screw it down tight to gag it.
It does I believe have a vent cap. There is something that drips into a copper tube the snakes it way through the walls from the attic all the way down to the basement where it can run into the floor drain if needed. I'll see if there is a way to shut it off. If so, that would be great.

Your problem wasn't caused by the plumber who opened the shut-off valve ahead of the pressure reducing valve.
He didn't open a valve there, he opened the valve just before the autofill valve that lets city water in. The way I see it, there is no way the system could overpressurize itself if there isn't any water being added. Am I wrong in thinking this?

What if the reducing valve had a small leak and over pressurized the system? That would certainly account for the relief valve opening.
I don't think I have a pressure reducing valve. What does one look like and where would it be in the system?

FYI, right now the system is cold and it is sitting at 16 psi. Shouldn't I be at around 7 psi when cold? When both zones get heated up the pressure runs about 27 psi. It never used to get this high.

Your tank is piped off the top of an air separator? Kudos to the installer. Even more kudos if (as Mike mentioned earlier) the piping is all sloping upward toward the tank, and even more if the piping is at least 3/4".
That is EXACTLY how it is plumbed.

After reading what you guys have said. Should I just try to drain some water out of the system to get the pressure down before going through all the effort to drain the expansion tank?

As always, I am very impressed with the knowledge base and the helpful attitudes found on this forum.

Thank you,
BWSwede
 
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Old 10-18-10, 05:36 PM
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Originally Posted by NJ Trooper View Post
I would venture to say that of all the system pics that have been posted here, I can't recall seeing ONE that was piped off the top of an appropriate air separator.
http://img183.imageshack.us/img183/8053/img0129m.jpg

http://img715.imageshack.us/img715/3636/img0131to.jpg

(In the second pix, ignore the coiled-up coax TV cable. The hose bib in the upper left is the expansion tank drain. The strap-on aquastat is my hi-hi limit control. In the first pix, the 1/2" black pipe is the natural-gas supply to my water heater; the 3/4" copper pipe is the cold and hot supplies of the water heater.)

This setup has been working fine for 60 years. Trooper, please check it out, and if you would be so kind, change your count to ONE. Thank you. Mike.

The boiler outlet has an Airtrol boiler fitting - a super-effective and super-old air separator (although still available from B&G). Its position is at the hottest point of the system, where air is least soluble. The pipe to the Airtrol tank fitting is sloped upwards, although the pix may not show it.

If I were now to completely replace my system, I might install a bladder-type expansion tank. Cheaper (plus might last as long as me), and I could lift it up by myself. Or, more likely, I would just replace the boiler and reuse the existing conventional tank.
 

Last edited by Mike Speed 30; 10-18-10 at 06:29 PM.
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Old 10-18-10, 05:45 PM
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Originally Posted by BWSwede View Post
I don't think I have a pressure reducing valve.
Yes you do. Pressure reducing valve = auto fill valve.
 
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Old 10-18-10, 05:51 PM
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Originally Posted by BWSwede View Post
FYI, right now the system is cold and it is sitting at 16 psi. Shouldn't I be at around 7 psi when cold? When both zones get heated up the pressure runs about 27 psi. It never used to get this high.
No, 16 psi is too high (cold) for a two-storey house. Should be about 12 psi.

27 psi (hot) - way too close to the 30 psi relief valve setpoint.

I think you overfilled the system (using the fast-fill valve), the pressure reducing valve isn't set right or leaking past the seat, or you didn't get enough air into the expansion tank before filling. Something is wrong.
 
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Old 10-18-10, 05:55 PM
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Originally Posted by BWSwede View Post
He didn't open a valve there, he opened the valve just before the autofill valve that lets city water in. The way I see it, there is no way the system could overpressurize itself if there isn't any water being added. Am I wrong in thinking this?
He opened exactly the valve I referred to: auto fill valve = pressure reducing valve. And, no, you are correct in your thinking.
 
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Old 10-19-10, 07:48 AM
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Originally Posted by BWSwede View Post
FYI, right now the system is cold and it is sitting at 16 psi. Shouldn't I be at around 7 psi when cold? When both zones get heated up the pressure runs about 27 psi. It never used to get this high.
When you drained your expansion tank, did you open the plug on the bottom of the tank, as we discussed? Otherwise, I doubt you would have gotten much if any air into it. You want the tank completely drained and full of air - then, when you repressurize the system (to say 12 psi cold), the level in the tank will be about right. And when the system is hot, the pressure should be less than 20 psi.

While you're removing that rogue air removal device in the attic, also replace the boiler gauge.
 
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Old 10-19-10, 12:13 PM
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Mike, I'm glad that the B&G Airtrol works for you but I, and many others that have had to fool with them think the Airtrol is the most useless thing B&G ever made.

I've also seen more than one of the "conventional" expansion tanks develop leaks from oxygen corrosion (rusting) right at the waterline maintained inside the tank. I always recommend that the water in such a system be treated with a corrosion inhibitor (which, of course, needs to be checked periodically) and to also use a nitrogen "blanket" over the water instead of air. Since this is pretty much out of the realm for a homeowner I far prefer the diaphragm expansion tanks.
 
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Old 10-19-10, 04:55 PM
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Mike Speed 30,

I haven't drained that system yet as I have been waiting for my bearing assembly to arrive (which it did this afternoon). Since we are now in heating season I (my wife) can't be without heat for very long so I want to get all the parts I need prior to starting the repair work.

Replacing the boiler gauge, is that something that is just a good thing to do every so often?

Maybe my tank isn't full as NJ Trooper suggested. Could it be that I just have too much water in the system. Should I just change out my pump bearing assembly and fill it up to 12 psi and then watch how high it gets when both zones are hot?

Thanks again for your time.

BWSwede
 
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Old 10-19-10, 05:24 PM
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When you drained the expansion tank, please tell us if you removed the plug at the bottom of the tank? Unless you did, it's doubtful whether you have sufficient air in the tank.

Is there "too much water in your system"? Probably, based on the cold pressure - but the pressure swing between cold and hot suggests that the tank's air cushion is depleted. You can drain the boiler down to where the cold pressure is, say 12 psi, and then see what the hot pressure goes up to. If it goes up beyond 18-20 psi, that pretty well proves that you didn't properly drain the tank - but I think you should know that already depending upon whether you removed the plug and completely drained the tank. I previously recommended that you replace the plug with a ball valve to make things simpler in the future.

Replacing the gauge isn't mandatory, but a good idea if it is more that a few years old or if the pressure/temp readings are suspicious. Bourdon tubes, after time, tend to read high. What is mandatory is ditching the air eliminator device in your attic.
 

Last edited by Mike Speed 30; 10-19-10 at 05:53 PM.
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Old 10-19-10, 08:47 PM
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Maybe my tank isn't full as NJ Trooper suggested.
BW, I didn't mean to suggest that YOUR tank was that waterlogged... I was kinda ranting generically there for a while! But, your pressure readings do seem to suggest that it may be at least partially waterlogged (as Mike sed)

The reason Mike keeps insisting that you 'pull the plug' is because of what I call "The Drinking Straw Analogy".

If you open a single tap at the bottom of a tank, water will exit... UNTIL a 'vacuum' forms at the top of the tank and the remaining water stays in the tank.

Liken it to placing your finger on the top of a drinking straw and removing it from the drink. The drink stays in the straw.
 
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Old 10-19-10, 08:53 PM
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Thanks for letting me know that I shouldn't have a large of pressure range as I do between hot and cold. The expansion tank is probably full. (I still blame the technician for leaving the valve open and letting water creep into the system.)

When you drained the expansion tank, please tell us if you removed the plug at the bottom of the tank? Unless you did, it's doubtful whether you have sufficient air in the tank.
I haven't drained the tank yet. Are you suggesting the tank can be drained without removing the plug? That gets me thinking...

If when I drain my system can I drain the expansion tank down through the 3/4" pipe the air bubbles travel up to get to it. It seems that if I open the manual vent at the bottom of the Airtrol fitting it would introduce air into the tank, thus breaking the vacuum and letting the tank drain via the air bubble pipe. Would this work? (I am trying to avoid pulling the plug on the bottom of the tank because it is around the corner of the room over some file cabinets, which I don't want to move.)

If you say that scheme doesn't work for some reason of physics, I will put a hose bibb on the bottom of the tank and drain it that way as you suggest.

Thanks again,
BWSwede
 
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Old 10-19-10, 10:09 PM
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I think that should work Swede... it's worth a try! I bet them filing cabinets are heavy... and I KNOW that plug ain't gonna come out without a fight.
 
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Old 10-20-10, 05:33 AM
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Thanks NJ. By the looks of it, the tank plug has been there for 60 years. I'm sure you're right, it aint gonna budge without a huge wrench sitting on it. It looks like I now have a plan of attack.

I opened up the box for my new bearing assembly last night and those things are a thing of beauty! You could even smell the fresh red paint. (I must be getting old...)

Thanks again,
BWSwede
 
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