Expansion Tank

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Old 02-26-08, 01:26 PM
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Expansion Tank

In the last fifteen years I have gone through 3 new expansion tanks. They are the standard bladder tank for a forced hot water system. I think they are pre-charged at around 14 lbs. but don't quote me. Manufactured by Watts which I think is the workhorse in the industry. The pressure relief valve is blowing off at 30psi and the automatic fill is around 12psi. How do I check the current one because tapping it sounds like its full of water. Would you recommend another brand? I have it screwed in the bottom of the air-scoop. Thanks. Joe A
 
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Old 02-26-08, 02:11 PM
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Wink

Do you get water out of the schrader valve ???

The pressure relief valve is blowing off at 30psi and the automatic fill is around 12psi.
When does the P./T valve go off???? When the heat comes on??? Or all the time ???
 
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Old 02-26-08, 02:39 PM
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Originally Posted by JoeA View Post
...but don't quote me...
Sorry Joe, I had to do that ...

You really can't tell much about the tank by tapping on it.

Nor can you check the air charge in the tank when there is pressure on the boiler. So, do this:

Turn off the boiler and let it cool to 100 or less.

Grab a garden hose, screw it onto any boiler drain, direct the hose to a drain or a bucket ...

Close the manual fill valve.

Open the drain and drop the boiler pressure to ZERO.

Close the drain.

Using a good quality tire pressure gauge, measure the air charge in the tank. It should be 12-15 PSI. If it's not, using a small compressor or a bicycle pump, add air until it is.

As Ed mentioned, if you get any water out of the valve, the tank is shot, otherwise you may only need to add air.

When you have the pressure where it should be, open the manual fill valve and let the boiler re-pressurize to 12 PSI (if that's the setting you are using).

Turn it on, and let it heat up and watch the pressure gauge.

I almost guarantee that you only have 5 PSI in the tank...

Realize that those tanks are a maintenance item. They don't hold the air charge forever. The bladder membrane will let small amounts of air past into the water. One manufacturer says about 1 PSI will be lost per year. Also, the tire valve can be leaky. Put some spit or soapy water on the valve to see if it's leaking. If it is, you can replace the valve easily. Any auto part store will have the tire valves and a small tool for replacing them...
 
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Old 02-26-08, 02:58 PM
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Any chance you could show a picture of how/where your exp-tank is mounted?
 
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Old 02-27-08, 09:02 AM
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Give me a maintenance free non-bladder type tank any day of the week. I hate doing things that cause more work. If the tanks are leaking it is an oxygen issue. For something to rust through you need steel, oxygen and water. Eliminate one of the three and corrosion does not happen. What type of system do you have? I see this more on low temp systems as they hold more oxygen. Heat the water up and drive oxygen out of the water.
 
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Old 02-27-08, 09:11 AM
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A picture of the boiler, tank and nearby piping would help.

If you really have the tank screwed directly into the bottom of the air scoop, then it may be that it's being subjected to a lot of heat fluctuations in the system and it's wearing out the bladder. A longish shot, but maybe. Put a short nipple into the bottom of the scoop, then a ball valve, then a couple feet of run to the tank. Put it on or near the floor, or otherwise properly support/suspend it.

My money is on rbeck, though -- oxygen in the system.
 
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Old 02-27-08, 10:04 AM
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The Schraeder valve is definitely leaking water when it is depressed. The system is a normal house set up where cut in is 170 degrees and cut off is 190. The airscoop is approx. 18 " above the top of the boiler and feed gate valve and the expansion tank is screwed into the bottom of it. I am on a well if it makes any difference. 3 zones. 3 circulators. I do get a bubbling sound at the boiler occasionally when it gets to 190 degree cutoff. I thought bladerless tanks were a thing of the past. I wish I knew how to send a picture but one of the notes in the post it page is telling me I can't.
Thanks to all. JoeA
 
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Old 02-27-08, 02:52 PM
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If you are getting water out the schraeder valve bladder is gone. What size boiler, what type of radiation and what model tank?
 
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Old 02-27-08, 06:52 PM
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The boiler is a 135000 btu Slant fin. The radiation is 8" forced hot water radiators. The tank is a Watts ET 60.
This is my third tank in fifteen years. Thanks
 
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Old 02-27-08, 07:26 PM
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Originally Posted by JoeA View Post
I wish I knew how to send a picture but one of the notes in the post it page is telling me I can't.
Joe, you can set up a free account at www.photobucket.com and upload your pics there, then provide us with a link to view the album.
 
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Old 02-28-08, 07:31 PM
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http://www.watts.com/pdf/es-et.pdf go here and scroll down near the bottom. They claim an Et-90 is the proper size with your boiler and cast iron radiation.
 
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Old 02-29-08, 07:55 AM
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expansion tank

Looks like a new expansion tank for me. Looking up the Watts specs, the finned tube radiators in a 135,000btu system calls for an ET30. Has any one else out there been having problems with Watts ETs or X-trol?? Seems like three tanks in 15 yrs. is a little excessive. Thanks
 
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Old 02-29-08, 08:29 AM
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Sorry had you confused with another post with cast iron radiation.
My guess is lack of maintenance. The pressure needs to be checked every few years. This is done with no water pressure on the tank. If the air pressure gets too low the bladder overextends and puts undo pressure on it. It will prematurely rupture.
 
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Old 02-29-08, 08:29 AM
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Joe, you should try and figure out how many gallons you have in your piping, boiler and emitters and anywhere you have boiler water. As rbeck stated, you're likely to have a very large volume system. One thing you can consider is doing a battery of ET-30s depending on what you find your system requires. Three ET-30s doesn't cost much different than an ET-90. You'll need a few more fittings, you'll need to make sure the ambient pressure of them all starts out the same and stays similar. Done right, you could tell with a tap when one goes and change it without even needing to shut the system down.
 
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Old 02-29-08, 08:33 AM
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The difference is when you do a 90 or 3-30's the tapping into the system should be 3/4" for the proper volume of water to move through at the right rate. It would probably work with slight pressure changes as the system heats and cools and the pressure equalizes.
 
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Old 02-29-08, 01:28 PM
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I've got at around 200' of 1" for feed and return in the cellar and probably that or maybe a little less of 3/4" finned tubing in the living area. The last 2 ETs were ET60s and the original looked like a 60 but it may have been a 30. I can't even imagine how to begin an estimate of the water capacity of the system including boiler. The idea of an ET being too small for the volume of water makes a lot of sense but I assumed the bladder expansion would be offset by the pressure relief valve which only seems to be blowing off when the ET has gone bad. Thanks for the ideas.
 
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Old 02-29-08, 03:30 PM
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Joe, the more that bladder moves the sooner it fails. Unlike most things hydronic this is one dimension where the bigger the better and money and space are the only restraints.
 
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Old 03-01-08, 12:46 AM
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I have very little experience with residential heating systems but I installed one for my parents way back in 1973. That diaphragm expansion tank lasted for at least twenty years that I know of.

I have also been intimately involved with several commercial systems and I never knew of a diaphragm tank failing although I HAVE seen several systems where the tank was either minimally sized or actually undersized.

Maybe I was just lucky.
 
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Old 03-01-08, 05:38 AM
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Unless this is a steam to water conversion I would not worry about calculating water volume. The manufacturers have the charts to assist in sizing tanks with a bit of a buffer built in. Are you running antifreeze? When the boiler is cold and you turn it on and it runs to temperature how much pressure change? It should be very minimal. Where is the tank in the system? What water temperature are you working with?
This problem should not be this difficult it an expansion tank. It's affected by water temperature, air charge and water pressure! That's it.
It's time for pictures.
 
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