Need Help With Procedure For Draining Expansion Tank


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Old 03-07-10, 02:50 PM
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Need Help With Procedure For Draining Expansion Tank

I have a 30+ year old slant finn boiler that has always worked well and still does. However, the pressure is pushing 30 psi after the boiler has run a while but settles back down to about 18-20psi.

I know from previous experience with this boiler since we've lived with it for 30 years that in the past this has happened for two reasons. 1. the overhead non bladder expansion tank gets full, and 2. the pressure reducing feed valve goes bad because we have hard water and it apparently allows the pressure to creep.

I've always had the company we buy oil from do an annual cleaning and I always provide the service tech who does it with some historical info like "the equipment is very sensitive to having the right nozzle size" and "if the pressure isn't between 12-15 psi at full operating temperature when he's done cleaning it then the pressure is too high" and the tank needs to be drained because its getting full.

Well, the knucklehead the oil company sent last fall to do the cleaning and service apparently thought I didn't know what I was talking about and said the operating pressure was OK at 18-20psi when he left. The pressure has gradually been going up during the heating season and now its pretty consistently at 28-30 psi after the boiler has run for a while.

I know the problem is either the overhead tank needing to be drained or the feed valve needing to be replaced because its been 5-7 years since it was last replaced.

I know from observing past techs who were inexperienced they never seemed to get all or most of the water out of the tank because they simply hooked up a hose to the drain valve and opened it. Then after 24-36 hours the pressure would be right up to 28-30 psi and the next tech would re-drain the tank by opening some other valves and the pressure would be fine after that.

I've done a search on high pressure and read just about every thread in the archives on the subject and have a pretty good idea about what to do to drain the tank, but there are a few things I'm unsure of and wanted to ask the experts here.

Specifically, what exact steps do I follow to drain the tank. I think I've got 1-3 right, its step 4 and beyond I'm unsure of.

1. Turn power off to boiler so it doesn't run while I'm working on it

2. Shut off the shut off valve between the pressure reducing/feed valve and the tank.

3. Hook up a hose to the drain valve on the tank and open the valve and let the tank drain.

4. What do I do to introduce air to the tank so it drains completely? My tank has some type of large red valve where the line from the pressure reducing/feed valve goes into the tank. There seems to be a plug of some sort on that valve? Do I need to remove that plug to allow air into the tank so all the water drains out? That plug looks like its below the bottom of the tank so will water come pouring out when I remove it? Or do I just loosen it to allow air to get in?

After the water is drained what do I do?


I guess if the pressure continues to rise after I completely drain the expansion tank then I have to look at replacing the pressure reducing/feed valve?

I would appreciate any help on how to proceed with draining the tank.

Thank you.

Dom
 
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Old 03-07-10, 03:24 PM
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Hi Dom, welcome to the forum!

If your pressure reducing valve is leaking through, there's no reason that you can't close the manual stop valve in the feed line once the pressure is correct... this will 'get you by' until you have a chance to replace it. You would need to keep an eye on the pressure occasionally though if you do close the valve.

The pressure on a COLD boiler should be 12-15 PSI. NOT on a HOT boiler... expect a hot boiler to be say 8 PSI above that...

You forgot a step in the draining procedure... hopefully it's not because you don't have a shut off valve in the line between the boiler and the expansion tank... most do, but some don't. Does yours?

1. Correct.

2. Not sure what you are saying here... What I said above about the valve between the boiler and the tank... or perhaps your water feed comes in somewhere on the line from the boiler to the tank?

3. Correct, once the proper valves are closed.

4. This will probably be easiest if we could see your system.

Got a digi camera? You can set up a free account at Image hosting, free photo sharing & video sharing at Photobucket and upload the pics there, and come back here and drop a link to the album... then we'll go from there... too hard to guess how your system is set up.
 
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Old 03-07-10, 03:40 PM
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NJ Trooper

I do have a digital camera so I will take some pictures and put the links here so everyone can see how my system is set up.

Thanks

Dom
 
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Old 03-07-10, 04:41 PM
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If I did the Photobucket load and update correctly the following link should bring you to the album I set up with 8 pictures of my boiler setup.

Pictures by coollx - Photobucket

I can add more pictures if needed, but I think what I've provided will show what I'm dealing with.

Thank you

Dom
 
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Old 03-07-10, 05:10 PM
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I added a couple of pictures to my Photobucket album that gives better detail of where the water feed line goes.

Use this link:

Slant Fin Boiler Photos pictures by coollx - Photobucket

Thanks
 
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Old 03-07-10, 08:02 PM
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Dom, I'm looking to see if there's a valve in between the boiler and the expansion tank that you can close to isolate the tank from the rest of the system. I can't tell from the pics because none of them show which of the pipes at the boiler is the one leading to the tank... maybe step back some steps and see if you can get a few shots that show the whole setup...
 
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Old 03-08-10, 04:16 AM
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NJ Trooper, there is not a valve between the tank and the boiler. The boiler is in the corner so taking pictures of it in its entirety is difficult. I'll see if there's a angle I can use that will give a better view.

Basically, the pipe from the pressure reducing feed valve goes horizontally to the left to an tee with one side of the tee going straight up to the expansion tank and the other side of the tee coming forward where it goes into the front right corner of the boiler. One of the pictures shows where it goes into the boiler.

Now that we know that there's no shut off between the expansion tank and the boiler to isolate the tank what do I have to do to drain the tank completely?

Btw, I believe from past memory that one time I remember a tech (who successfully drained the tank) shutting off some of the valves in the front left side of the boiler that are situated above the two taco circulating pumps. Then he may have connected a second hose to one of the faucet type valves just below one of those inline shutoffs? Could he have been introducing air to the system by doing that so the expansion tank would drain completely?

In the meantime, I'll see if I can take a better picture.

Thanks

Dom
 
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Old 03-08-10, 04:41 AM
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NJ Trooper,

I just added three additional photos that I believe will give you a better idea of the setup. The third picture to the right in the first row of pictures clearly shows what I previously described regarding the path the lines from the pressure reducing/feed valve takes to the boiler.

You should be able to click on the last link and see all the pictures including the three lastest ones.

Hopefully, you have a suggested approach for me to safely drain the tank and get the boiler up and running again.

Thanks for your continuing help. This is just a great forum for those of us that have some knowledge but not quite enough.

Dom
 
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Old 03-08-10, 08:34 AM
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For a basic standard tank installation and how to drain see the link below.
Technical Menu
Choose hot water boiler and in the lower right corner click on draining tank link.
 
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Old 03-08-10, 09:04 AM
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rbeck,

The first problem I have is that there's not a valve to isolate the tank from the boiler so I need some help with an alternative approach.

Dom
 
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Old 03-08-10, 03:25 PM
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Hi Dom, I might have to cut this off in the middle, but if I do, I'll come back and finish it later...

The red thing on the bottom of your tank is a Bell&Gossett ATF, and it has a 'tube' that runs up to what is supposed to be above the water line in the tank. The intent of the device is to make it easier to maintain the water level on initial filling of the system. It doesn't do much when you have to drain the tank, but it MIGHT help to open that little tap on the bottom.

B&G instructs in the installation for this thing that it is NOT necessary to install a valve in the line from the boiler to the tank, but honestly, I have no idea why they would suggest that. It just makes it that much harder to drain the tank when it's necessary... sure, in a perfect world, the tank would never need draining, but this ain't a perfect world... not by a longshot.

In the pics I see that there are valves on the RETURN lines to the boiler, but I can't tell if there are also valves on the supply side... I suspect that there are not. You DO have flow check valves though... and they may help to keep the water up in the system... so you don't have to drain the whole thing...

You could just shut off the water supply, and the two shutoff valves on the return lines, and with a hose on the tank, open the drain. The pressure in the boiler will be relieved, and you will see the gauge go to zero...

When it does, try opening the tap on the bottom of the ATF and see if it sucks air... it might.

Do you have a small air compressor by any chance?

bbl
 
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Old 03-08-10, 04:33 PM
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Yes, I have an air compressor.
 
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Old 03-08-10, 07:23 PM
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Dom, you might be able to fashion a fitting for the bottom of the ATF device that will allow you to add air to the tank via the compressor.

I'm thinking out loud here, and this might be a flawed idea, but lets chew on it for a bit...

I would come off the bottom with a nipple, then a ball valve, and an air fitting. Turn the regulator on the compressor down to something like 15 PSI.

Check that the boiler is also right around 15 PSI.

Hook up your drain hose, close the water feed valve.

Open the drain hose and open the valve to the compressor. WATCH THE PRESSURE GAUGE on the boiler while doing this... if the compressor is set at 15, it shouldn't go too high... but watch it anyway...

The idea is to feed air pressure into the tank through the ATF and forcing the water out the tank drain. This _should_ eliminate the need to drain the boiler, while getting air into the tank, and displacing the water.

Once the tank is empty, shut off the air FIRST, and then the tank drain. The object is to have atmospheric pressure in the tank... in other words, no 'extra' air pressure. When you close the drain valve and re-open the water feed, it should re-pressurize the system to the nominal 12-15 PSI. You WILL hear water flowing into the tank, and that is NORMAL. Normal operation that tank will be 1/2 or more full of water. The other half will be the air that was in the tank now under pressure of the boiler.

Our friend furd who posts here has given similar advice... maybe he will post up and add his comments.

You might consider adding a valve in the line...
 
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Old 03-09-10, 04:23 AM
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I can work on rounding up the parts you are suggesting to give this approach a try.

One question I have is whether the air I feed into the ATF device will also flow back into the boiler since there is not a second valve to isolate the boiler from the tank? Or is this the reason for having the boiler and the air being feed into the ATF both at 15 psi?

Once the heating season is over I will add a second inline shut off valve between to tank and the boiler so in the future I can isolate the expansion tank for draining.

Thanks for your continuing assistance.

Dom
 
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Old 03-09-10, 07:59 AM
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targa, you might want to go to the bell & gossitt sight for a better understanding of the ATF you have. It's explained there. That screw at the bottom is to set air in to break the vacuum so water can be released.
 
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Old 03-09-10, 09:39 AM
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While it (the tap on the bottom) should and will work that way, that's not the purpose of it... according to B&G.

In any case, without a valve in the line between the boiler and the tank, there is no way to easily drain the tank...
 
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Old 03-11-10, 10:54 AM
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I drained my expansion tank two days ago. First I hooked a hose up to the drain valve after shutting off the pressure reducing/feed valve and let the water drain until it stopped. Then I put air pressure into the tank through the ATF as suggested and more water came out but not a whole lot which surprised me. Maybe I'll need to do it again?

Once I finished draining the tank and closed all the valves, I opened the valve for the pressure reducing/feed valve and let it pressurize the system. When the water stopped flowing the pressure settled in at about 12-13 psi when the boiler was cold (100 degrees).

I have run the boiler continuously for the last two days and the pressure is about 20-21 psi when the boiler shuts off at 200 degrees. When the temperature drops to 140 the pressure is around 18 psi. Does this sound normal?

If the pressure is going to rise back up to 28-30 psi, how long will it take in hours or days for it to happen?

Thank you.

Dom
 
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Old 03-11-10, 03:16 PM
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Sounds like yer on the right track now Dom...

The pressures you cited sound fine.

If the pressure reducing valve is faulty, it can take days, or even weeks, depending on how fast it is leaking through for the pressure to creep up.

If you do see the pressure starting to climb slowly, let the boiler cool to 100 or less, and if it is above 12-15 PSI, drain a little water off until the pressure comes down to that... then CLOSE the manual water feed valve and run the boiler for a period of time (days, weeks) and check the gauge periodically. If the reducing valve IS leaking, you should now see the pressure NOT increase...
 
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Old 03-15-10, 11:15 AM
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There are two types of air management systems.
Air removal which is used in new installations where you have automatic air vents. The other being Air Recovery where the air scoop is piped directly to the bottom of the expansion tank. This type usually will have a sight glass on it. And You Should not have any air vents installed.
The biggest cause relief valves blowing on the Air recovery system is people installing automatic air vents in there systems. Do you have any automatic air vents installed? What this does is removes the cushion of air in your tank and your tank gets water logged . Causing the pressure to rise when the water is heated and subsides when it cools.
 
 

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