Overflow expansion tank in attic

[Anonymous]

We have an historic home complete with the big radiators and a 50 gallon expansion tank in the attic. About 10 years ago we had a new boiler put in and asked that the attic expansion tank be removed from the system with a new tank installed in the boiler room. The plumbers said they couldn’t disconnect the tank in the attic but they did put in the new tank in the basement. Now water is coming down the overflow from the attic tank (via a wierd series of pipes and old hose!). Our plumbers are all out fighting fires (this is Montana) and we were advised to replace the reducing valve so we did that but on starting the fill up, the overflow started again. Could this mean the new expansion tank needs to be recharged? If so, how do we do that exactly — we know it can be pumped with a tire gauge but how does one isolate it, and then to what pressure should it be filled? If this is not the problem what is??? Thanks, Cris

[daveroconnParticipant]

The only way an expansion tank can drain is for air behind the bladder to push it out. If your tank does not drain completely than it does not have enough air in it to displace the water inside.

If you have air in your water than your expansion tank needs to be replaced because the bladder has a hole in it.

To drain an expansion tank

First you need to drain the tank as far as it can go by itself. Next using a bicycle tire pump add air to the tank only until the water begins to flow out. Do not over pump the tank or you may ruin the bladder. Keep doing this until you are sure all of the air is out of the tank. Now to obtain the propper air pressure this can only be checked with the tank empty. Most 75 gallon well tanks use 30 to 38 PSI empty. Now it would be a good time to disinfect the storage tank with some bleach. Use an empty filter sump housing to introduce about a 1/4 cup of bleach into the tank you will need some valves to do this. Now rinse the tank by filling it and draining it sevrall times.

[Harold KestenholzParticipant]

This is a problem of age. The people who knew what part was which and why when they put the gravity system in have passed away.

The expansion tank in the attic was all that was needed when the system was installed. It is a 50 gallon tank because the water in the system can be as much as 1000 gallons. That much water will expand an extra 40 gallons when heated to 180F. If they did not change the system to new copper tubing, but left the old large pipe, there can be that much water in the big pipes and radiators. That is about 4 tons of water.

The old attic tank is still there for some good reasons besides the amount of water. If you remove the old tank and seal the sytem off to be a modern pressurized system, high pressure can turn your old pipes into an unregulated sprinkler system. Also, the people who put the new tank in the basement will have to put the right size commercial bladder expansion tank in the basement, or about 30 of those little tanks in the basement to take care of all the expanded heated water.

I wouldn’t worry about the little tank in the basement. The problem comes from having the automatic fill or pressure regulator attached to the line. The attic expansion tank has those pipes and hoses up there because the tank was supposed to be hand filled periodically. There is most likely a handle in the middle of an upstairs bathroom wall that doesn’t turn anything in the bathroom on, but when it is opened, eventually water spills down a pipe into the tub or a sink. That was the fill and spill, when water spilled – the tank was filled.

The new automatic pressure regulator has to be set just at the point where water will not spill out the top. This is too tricky a job for most, and as the regulator ages, this will have to be readjusted. So when the water spills from the top, close the valve and shut off the regulator. Once a month or so, open the valve, let the water spill, then shut it again and your historic museum-piece heating system will function just the way our forbears intended.

The people who really know about this yet are the blokes in Great Britain. Why use a pump when gravity does the job for you just as well?

[SylvanLMPParticipant]

Normally you when Install a new automatic feeder, they are factory set at 12-15 PSI
outlet pressure.

OK here is where it gets tricky. If you take the pressure times 2.31 it will tell you how high this will elevate the water.

Also on systems where your not sure how much pressure you actually need, try to do the following.

Measure from the boiler to the top of my highest radiator and take this number and times it by . 434 (no flow conditions) BUT also add another 10 ft of static head so you know you have a positive pressure in this system (keeps air out)

Example 50 ft static head . 434 = 21.7 PSI

To prove take 2.31 times the pressure 22 PSI would equal 50. Ft approx.

Add the fudge factor and then size your expansion tank accordingly as when this water is heated it will expand.

To find the total gallons required to fill this system, All you do is drain it filll it up through a water meter and it will give you the measurement in cubic feet (7.48 gallons) this would you help you in sizing the actual volume your dealing with.

Personally I love open tank systems as you know you have a constant head pressure. Air in the system will find its way to this open tank and NOTHING mechanical to fail. Of couse it this tank does leak flood city LOL ( hey you cant have everything)

[SylvanLMPParticipant]

I forgot to add the following.

If you fill the system the system and look at the altitude part of the compound gauge this will give you the static pressure.

Easiest way fill the system until water flows out the highest rad.

Check out the gauge THEN add 5 PSI more and this is your set pressure.

[jimncrisParticipant]

I really appreaciate the help you are sending. We are trying to follow the ideas (I’ve had just enough physics to be “dangerous”)I forgot to ask why this is suddenly happening. To me it means the “new” expansion tank has failed. It is about 20″ high and less than a foot in diameter. The attic on is 50 gallon. It has a clear tube to gauge how much water is in it. We also have a guage in the basement the owner (original family member for the house) told us regulated how high the water went in the house. It is regulated by a valve that comes from the outgoing stacks. Is this the valve you were talking about Mr. Kestenholz? We have kept the tank in the attic empty according to the tube guage and the regulating guage so why is it that when we allow water in the system it now is running out the hose end of the overflow pipe (in the basement)? ~ Cris

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