Pressure fluctuation

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  #1  
Old 01-08-05, 07:14 PM
CMarkT
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Pressure fluctuation

It appears that I need to drain my expanion tank because the pressure in my hot water system is increasing 10 to 12 psi when ever the boiler kicks in. The system otherwise is silently heating my house just fine and I'd like to keep it that way. I'm not very familiar with boiler type heating systems, so I just want to make sure I'm not going to reck something in the middle of winter.
the water enters the expanion tank through an Airflow tank fitting (?) and the tank it self has a garden hose type faucet coming out the bottom.
It looks like I want to shut off the expansion tank from the rest of the system and drain the tank using the faucet while allowing the tank to breath through a valve on the Airflow fitting. After the tank is drained and system valves are open again, I'll need to add water to get the system back up to 10 psi (basement of a one story house).
Hopefully this will lend itself to a quick painless response, but if you have a minute, I'd appreciate it if you could tell me what an Airflow tank fitting is and if I actually know what I'm talking about or not.

Thanks,
Mark
 
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Old 01-08-05, 08:05 PM
A
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Welcome to the DIY Forums

Mark,

Is what you are calling an "air flow tank fitting" like a bicycle tire valve, i.e. a Schrader Valve? This is normal on a bladder expansion tank, and they come factory set at 12 psig. Use a tire gauge and check the pressure on the tank. If you depress it and you get water out the bladder is ruptured, and you will have to replace the tank.

If no water comes out, but you have low pressure, use a bicycle pump and pump the pressure up to 12 psig.
 
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Old 01-08-05, 08:30 PM
CMarkT
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Thanks for the response.
It's not a shrader valve. It has a tag on it that says Airtrol (not Airflow, sorry) tank fitting, size ATF 12. It has a patent number too, it that would be helpful. Red and about 6-7" long, 2.5" wide. Water would have to go through it to enter the tank. Any ideas? I took a digital picture, but I obviously can't add it to the post.

Thanks again,
Mark
 
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Old 01-08-05, 09:03 PM
CMarkT
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It really helps when searching google with the right name.
The Airtrol tank fitting is the one on the far right at the top of this PDF;
http://fhaspapp.ittind.com/literature/files/599.pdf
It looks like I just open the valve on the bottom of this fitting until it stops draining?
 
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Old 01-09-05, 05:54 AM
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The Airtrol setup was a good system. It was made up of 2 parts. One part went on the boiler and the other went on the expansion tank. I hope your boiler still has the air trap part on it. It will be red in color and shaped sort of like a bell. It will be installed on the supply outlet of the boiler. What you need to do is isolate the expansion tank from the boiler. Then open the drain and you can also open the small hex plug on the airtrol fitting at the expansion tank to admit air to the expansion tank. When the tank is empty, close the vent and open the valve to the system. If you have both parts of the airtrol system, (and ONLY if you have both) as the system fills, open the vent plug again and close it as soon as water comes out. If you only have the tank part, don't let any air out at all. Post back if you have any more questions.

Ken
 
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Old 01-09-05, 07:58 AM
CMarkT
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Thanks for the info, Ken.

I'm starting to understand what a confusingly "cusomized" boiler system I have.

The boiler doesn't have the air trap part that you described, but it does have a loop of piping that appears would have the function of directing air to the expansion tank. After coming out of the boiler air is either going to go 3 feet up to the expansion tank or 2 feet straight down before going back up into the radiators. Also, what that PDF describes as the cold water supply enters the boiler seperately and has a pipe that leads up and feeds into the one going expansion tank as well.

It's too bad I couldn't post a photo album of the darn thing.

If you could explain the purpose of that Airtrol fitting, I think I would feel more confident about draining the expansion tank. It'll happen either way, but it might help to reduce my paranoia.

I really appreciate the help,
Mark
 
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Old 01-09-05, 05:01 PM
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The part of the airtrol fitting you have is nothing more than a vent now to get air into the tank when you drain it. Back in the day, the part that went on the boiler had a pipe that dipped down a few inches into the boiler. That pipe was connected to the heating system. Then the outer part of the fitting trapped air at the top of the boiler and sent it up to the expansion tank. It did such a good job that the expansion tank had to have more water than normal in it and that is why you would have to open the vent and wait for water. It would reduce the amount the amount of air in the tank. You don't want to do that. Just drain the tank completely and reopen the boiler supply to the tank and all should be well.

Ken
 
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Old 01-09-05, 10:09 PM
CMarkT
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Thanks again Ken,

The tank has been completely drained and the pressure now only increases about 5-6 psi (about half of what it was doing before) when the boiler reaches it's max temp. It now increases from 11 psi to about 17 psi.

Is that reasonable or should I be shopping for a new expansion tank?
 
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Old 01-10-05, 07:45 AM
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That sounds fine. Problem solved.

Ken
 
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