Expansion tank full?


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Old 01-26-07, 10:42 AM
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Expansion tank full?

When I put my hand on the expansion tank the bottom and top are warm - almost like it's full of water. Isn't it supposed to be about half full at all times? I have drained about 3-4 gallons out of it but it always seems to fill back up. I've had persistent water banging and am wondering if it's from this tank being water logged...

http://s105.photobucket.com/albums/m213/cassellgrafx/?action=view&current=Furnacediagram1b.jpg

The tank (#1) is an 8 gallon. Valve #4 is always open. The vertical pipe from where valve #4 is located, goes to the tank above and down to the boiler below. I drained the tank with valve #2. It seems like the tank would just keep re-filling full with the way the pipe is set up. Any ideas? Thanks.
 
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Old 01-26-07, 10:56 AM
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This might sound like a silly question, but when you drained the 3-4 gallons out, did you actually let 3-4 gallons of air back in? If not, you did nothing. It's hard to get any replacement air in those tanks unless you drain the whole thing.

Do you bleed your rads or purge air annually or more?

(nicest, best labelled pic ever - just call it a boiler next time <g>)
 
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Old 01-26-07, 11:04 AM
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addendum

To drain your tank...

Close your feed valve and #4, open #2, let it drain completely.


Once fully drained...

Then close #2. Then slowly open your feed valve and let it fill as slow as possible. Then open #4 very slowly... once equlaized, open #4 fully and close your feed valve. You will be introducing lots of little bubbles which make the whole deal a revolving circus.


Personally, I'd get rid of that tank and put in a diaphram type compression tank. You do have the advantage of a very long drop from the tank but air can still go into solution and end up other places. Even with the tough challenge it gets on yoru system.
 
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Old 01-26-07, 11:42 AM
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Thanks Who! OK, your explanation makes sense - but I'm not sure what the feed valve is. Is it the valve that lets water into the boiler from the house water supply? I thought that stayed open always. How do I know when it's equalized upon refilling? Thanks.
 
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Old 01-26-07, 11:57 AM
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Yes, the feed valve feeds domestic water into the boiler. When draining the expansion tank, I would turn it off, until you are ready to fill. I should also point out to shut off the boiler while draining the tank. It' obvious to most, but if you don't the pressure will go crazy with the tank isolated from the rest of the system as the water heats and tries to expand with nowhere to go.

If you boiler doesn't leak, why leave the feed valve open?

If the boiler does leak, how will you know if your feed valve is open?

If it leaks fast, a closed feed valve means there is only so much to leak.

Do you have a LWCO device to stop the boiler if your water is too low? You should... it's a key safety device. If you don't, then there is debate as to whether or not it should be left open. Dry fired boiler verses flooded home. A LWCO ends this debate.

As for equalization, you'll hear when the water stops moving. We aren't pros so we can fill the tank up reeeeeeeeeeeally slowly, the feeeeeeeeed too. ;-)
 
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Old 01-26-07, 12:11 PM
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Makes sense. No the boiler doesn't leak. The drain valve on the boiler itself drips 10-15 drops every day so I guess technically that's a leak. I'm planning on replacing that valve once it's spring time and "safe" (no home heat needed) to work on the thing - maybe a good time to switch for a diaphram style expansion tank and LWCO device as well. Thanks again!
 
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Old 01-26-07, 01:17 PM
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You could twist a little drain cap onto that. Not a bad idea in general to have those on, especially if there are small futur D-I-Yers around.

A leak like that will decrease your pressure over time.

Some valves can be tightened by tightening the packing nut that the handle goes through.
 
 

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