Compression tank

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  #1  
Old 10-11-09, 08:09 AM
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Compression tank

All,

I have been experiencing a 13 psi jump in pressure when my entire system is heated up to 180 degrees. This is causing one of my pressure relief valves to open slightly (at 27 psi). I have been reading the archives and it appears that my compression tank may be waterlogged. My question is how did it get that way.

I have a Burnham boiler that only provides heat to the house. I have a shut-off valve before the autofill valve that is never open. Since I don't heat my domestic water with the system there is not a coil in the water tank.

For me to gain the extra water in the system both my autofill valve and the shutoff valve before it must be malfunctioning, or is there another explanation for my compression tank to become waterlogged. I have the two part Bell and Gossett system for capturing air in the system. I have the Airtrol boiler fitting and the Airtrol tank fitting.

I know the solution is to drain the compression tank but unfortunately it does not have an isolation valve to aid in the process. Therefore it seems that I have to drain the whole system before I can remove the plug on the bottom of the compression tank. Is this correct?

Thanks in advance,
Blane
 

Last edited by BWSwede; 10-11-09 at 08:44 AM.
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  #2  
Old 10-11-09, 08:25 AM
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auto fill should be lock nutted to maintain 12lbs incoming pressure cold.definitly isolate the line to the tank and add a bleed off..water has no place to expand at the temp limit.
 
  #3  
Old 10-11-09, 09:58 AM
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I have the two part Bell and Gossett system for capturing air in the system.
I need to look at your pics again... I don't remember if they showed this or not... but, if you've got a steel tank, there should be NO auto air vents on your system. You certainly may have the 'air scoop' but the expansion tank should be plumbed to the TOP of the scoop so that any air it traps goes back to the tank.

IF you have an auto air vent, then what happens is that slowly, over time, the air that was originally trapped in the tank dissolves into the water, and is expelled by the vent.

Do your pics show this part?

Yes, I agree that you should probably install an isolation valve if you don't have one, and yes, you may have to partially drain your system... you may not have to drain it all the way though... it all depends on how much you can isolate by valving off, and how quickly you can work. I don't usually recommend this, but you could install a ball valve with compression fittings on the line to the tank, and this would alleviate having to get the pipes dry in order to solder the valve in.

It is _possible_ that local building codes in your area forbid isolation valves in the line to the expansion tank... for protection against an accidentally closed valve. That _could_ be why you don't have one.

There is an alternative that involves an air compressor... maybe furd can tell you about that?
 
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Old 10-11-09, 10:09 AM
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Blane, put up some more pics in your album to show the rest of the piping:

Boiler pictures by BlaneS - Photobucket
 
  #5  
Old 10-11-09, 11:24 AM
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There is an alternative that involves an air compressor... maybe furd can tell you about that?
Of course you need the air compressor if you are going to do this. You need to make up an adapter from the air hose quick-connect to mate with the garden hose connector on the expansion tank. You also need a pressure regulator on the air compressor.

After installing the necessary adapter from the air hose to the expansion tank drain adjust the air pressure regulator to about 20-25 psi. Open the drain valve on the expansion tank and this will pressurize the entire system to the setting of the air pressure regulator. Close the drain valve on the expansion tank and open the drain on the boiler to blow out water until the pressure on the boiler is back to a normal reading. You may need to do this more than once if the expansion tank is really full of water.

After getting the proper pressure on the boiler remove the air hose and adapter from the expansion tank. Screw a garden hose cap (with rubber gasket washer) on the drain from the expansion tank.


I did not re-read the entire thread but if it were my system I would likely do a complete rewire (to eliminate the problem wiring and extra relays) and also install a bladder-type expansion tank.
 
  #6  
Old 10-12-09, 07:27 AM
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All,

Thank you for assisting me with my pressure issue.

IF you have an auto air vent, then what happens is that slowly, over time, the air that was originally trapped in the tank dissolves into the water, and is expelled by the vent.

Do your pics show this part?
I took a picture of a bluish-green bulbous device up at the highest part of the pipes up in my attic. It is connected to a small tube that is inserted into a larger tube that drops down from the attic through my main floor walls and into the boiler room in the basement. I am assuming it does this so that if any liquid comes out it runs down the tube to the boiler room floor drain. Boiler :: Air Vent (?) up at the highest point in the attic picture by BlaneS - Photobucket I am assuming that this is the auto air vent you are asking about.

I have attached more pictures of my systems here:

Boiler pictures by BlaneS - Photobucket

After installing the necessary adapter from the air hose to the expansion tank drain adjust the air pressure regulator to about 20-25 psi. Open the drain valve on the expansion tank and this will pressurize the entire system to the setting of the air pressure regulator. Close the drain valve on the expansion tank and open the drain on the boiler to blow out water until the pressure on the boiler is back to a normal reading. You may need to do this more than once if the expansion tank is really full of water.
I don't have a valve on the compression tank drain, it just has a pipe plug. I think I understand the process and concept of what you are describing, but I am thinking that I can't do that until I have a valve on the bottom of the tank. Correct?

I did not re-read the entire thread but if it were my system I would likely do a complete rewire (to eliminate the problem wiring and extra relays)
Since it is working as designed now I think I'll leave it until it gives me problems again.


and also install a bladder-type expansion tank.
Thanks for the suggestion. The system I have has lasted 57 years. From reading the archives it seems the bladder type tanks fail after so many years and need replacing. What is the advantage of the bladder tank over the compression tank?

Thanks again for the help guys. If you need more pictures just let me know.

Blane
 
  #7  
Old 10-12-09, 09:48 AM
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That air vent needs to be removed from the system and the line capped. There appears to be no way to isolate it, so it seems that you're going to have to drain the system anyway - drain and vent the expansion tank at the same time. Refill the system and bleed all the radiators. You're done in short order.

For reasons previously explained, an air vent and conventional expansion tank can't co-exist.

I take it that it doesn't get very cold there. I noticed the piping in the attic and daylight shining through the eave.
 

Last edited by Mike Speed 30; 10-12-09 at 12:14 PM.
  #8  
Old 10-12-09, 01:46 PM
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Mike,

Thanks for the reply. Drain the system, add valves, fill, and bleed. I'll have to think about this awhile to see if I feel up to it or weather I should call in the reinforcements.

As you noticed there is piping in the attic, but it is only the hydronic heat piping (no domestic water pipes). When I first saw this when looking to buy the house it concerned me. After some thought I realized the when the system is running it is not a problem. When the system shuts off all the warmest warm migrates to this area via gravity. During our cold spells in the low to mid teens (it doesn't get very cold here) the boiler kicks on every few hours pushing warm water through the pipes. When we loose power during the cold spells I run the circ pumps via generator.

There are a couple areas where I can see daylight through the eave but with all the code required attic vents in the roof, closing the cracks won't accomplish anything but eating up my time.

Thanks again,
Blane
 
  #9  
Old 10-12-09, 03:32 PM
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Originally Posted by BWSwede View Post
Drain the system, add valves, fill, and bleed. I'll have to think about this awhile to see if I feel up to it or whether I should call in the reinforcements.
You need to cap the system where the air removal device is now connected. You can buy a pipe cap at the hardware store.

Adding a drain valve to the expansion tank should involve removing the plug with a pipe wrench, and installing a nipple and a sillcock or hose bib.
 
  #10  
Old 10-13-09, 07:36 AM
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I am mentally going through the steps to complete the procedure and one thing I can't figure out is how to get the air out of the very top pipes. My house has a basement and a main floor. The basement is all fin tube units fed from above, no air traps here. The main floor has 5 fin tube units fed from below, each one has a bleeder on it. The rest of the main floor system is in wall and ceiling radiant heat. How will I get the air out of the return pipes in my attic? Should there be an air bleeder up there like I have now? Maybe it needs to be a manual bleeder that can be shut off as compared to the auto bleeder (is that what I have?) currently in place.

Thank you,
Blane
 
  #11  
Old 10-13-09, 10:44 AM
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Yes, a manual bleeder would be good - where the air removal device is now (in the attic). You could use just a small ball valve.
 
  #12  
Old 10-13-09, 03:35 PM
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I was gonna suggest that... beat me to it! good on ya mate!

One thing that's gonna happen is that when fresh water is added to the system, and it gets heated, air will come out, and it will collect up at the high points... so, after you drain the tank, and add fresh water, you may have to operate that valve up top several times... which is gonna get to be a PITA.... so, what if you put a valve on the line to the vent, and leave the air vent in place, with the valve open, until the air is outta the system, then shut the valve?

Then, after you have the valve installed in the line to the tank, and all the air is outta the system, you can easily go back one more time, and re-drain the tank, and be done.

I think I would insulate those pipes in the attic...
 
  #13  
Old 10-13-09, 03:53 PM
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You know, I've never thought of it: if I didn't live in a cold area, a bleeder line extending into the attic might be a nice feature.

But Yes, absolutely, insulate that bare, horizontal line that now goes to the air removal device (and will now go to a new bleeder valve). Better yet, remove that uninsultated horizontal line and install the new bleeder valve over on the end of the insulated vertical piping run.
 
  #14  
Old 10-13-09, 03:57 PM
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NJ,

Great idea putting the valve before the auto air vent. I'll do that.

I followed everything else you said except for the part about draining the tank one more time. Is the compression tank going to fill up when I fill the system?

Thanks,
Blane
 
  #15  
Old 10-13-09, 04:11 PM
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Originally Posted by BWSwede View Post
I followed everything else you said except for the part about draining the tank one more time. Is the compression tank going to fill up when I fill the system?
I think I can read Trooper's mind.

The answer is Yes and No.

Yes, as air is removed from the system and diverted to the expansion tank, it might get completely filled, and more, with air. No, not filled with water.

After you've bled air from the system and run the circulator, isolate the tank and drain the tank. Shut the tank's drain valve and open the tank's iso valve. The tank will then flood to its proper level.

Otherwise, maybe the tank might wind up with 100% air, which wouldn't be good.
 

Last edited by Mike Speed 30; 10-13-09 at 05:02 PM.
  #16  
Old 10-13-09, 04:37 PM
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I think I can read Trooper's mind.
I could say something nice...

like: "Great minds think alike"

but self-deprecating humor is more my style...

Mike, it's a VERY short story!

Blane, what Mike said... after the system is up and running, and air all bled out, just re-drain the tank one last time to insure the proper levels in the tank.
 
  #17  
Old 10-13-09, 04:59 PM
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To drain the tank I am assuming that I need to open the air valve on the Airtrol valve to introduce air into the top of the tank, otherwise wont the water just hang in there?

Many thanks,
Blane
 
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Old 10-13-09, 05:09 PM
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Yes, that sounds correct...

You did say you were going to install the tank isolation valve, right?
 
  #19  
Old 10-13-09, 05:12 PM
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I thought the plan was to remove the plug from the tank, and install a drain valve? Are we thinking differently here? (Otherwise, your stated plan might work, but I'd need to think more.)

Please double check that there is not already a drain valve on the tank. It would be surprising if there were not.

Once you close the iso valve to the tank, and open the tank drain valve (if it's there), the tank will gurgle out water while air enters. When finished gurgling, the tank will be full of air (at atmospheric pressure, 0 psig).
 
  #20  
Old 10-13-09, 05:19 PM
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Yes, I will install an isolation valve for the tank. I will also remove the plug from the bottom center of the tank and put in a valve with a garden hose thread.

It sounds like I don't need to mess with the Airtrol valve. My fear is that by doing so it will slowly start leaking the air out of the tank.

One last question, do you think it is possible to close the auto air vent valve up in the attic by tightening a nut or bolt? If so, I wouldn't have to remove that valve to put in a shutoff valve upstream. I thinking it might be like the bleed valves on the fin tubes I have.

Thanks again guys,
Blane
 
  #21  
Old 10-13-09, 05:31 PM
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Originally Posted by BWSwede View Post
do you think it is possible to close the auto air vent valve up in the attic by tightening a nut or bolt? If so, I wouldn't have to remove that valve to put in a shutoff valve upstream. I thinking it might be like the bleed valves on the fin tubes I have.
You'd have to look at it. Maybe just thread in a plug or cap on the outlet of the air vent?

If you do remove the vent, it wouldn't be necessary to add a valve upstream. A new bleeder would be fine.

If you've got bleeders on the fin-tube units, then a bleeder in the attic wouldn't be necessary. But one way or another, the existing air removal device has to go - or somehow the outlet plugged.
 
  #22  
Old 10-13-09, 08:43 PM
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Unfortunately the Hoffman (brand) vent in your attic does not have any means to close off the vent. You need a valve before the Hoffman.
 
  #23  
Old 10-15-09, 03:29 PM
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Originally Posted by furd View Post
Unfortunately the Hoffman (brand) vent in your attic does not have any means to close off the vent. You need a valve before the Hoffman.
Another idea: replace the existing vent with an old, reliable Maid-O-Mist (comes with a cap). No additional valve needed.

Another thought: what pressure is your boiler running, cold and hot? For a 2-storey house (with boiler in the basement), 12 psi (cold) is about right. But with that jobadoo up in your attic, I would add about 4 psi - it's almost like a 3-story house.
 
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