STORAGE QUESTIONS

[leaddog]

This is the expansion tank I'm using. I think its 330 gallons and it's off a field sprayer. It's just like a propane tank and I just ran a line from the bottom into my boiler line. The amount of water in the tank goes up and down approximately 12"s when I change from 125 degrees to 190 degrees. I have not added any air to this and I'm in my second year.

How do you initially set this type of system up?Do you add air to the expansion tank or do you simply just add the tank once the rest off the system is full ?Do you have a make up water system also? Thanks Jeff.

lWe plumbed the tank into the system and as the system was filled it compressed the air and that gave it the pressure charge. If you look hard at the green tank that SDRobertson put up you will see some markings on the side. They were calibration marks I made as I filled it with cold water to pressure test. I could see the water line from condensation moving as the water filled and I marked it to corespond to the gage.
If for some reason you would have to add air you can just add air with the air valve and let out the amount of water you need to . We don't use a makeup system but you could. We don't as you will never have to add water if you don't have a leak and this way we will know if we have a leak. Remember we are both using 2000+gals so if we have a leak that makeup water is trying to make up to keep the boiler wet we have a HUGE problem. We would rather know if a small leak develops.

 

[Jeff S]

Leaddog.thanks for the info.I all ready have my system plumbed with a bladder tank,but if I decide to add more storage later this could be a option.

 

[DaveBP]

You fellows using propane tanks (steel tanks without bladders) as expansion tanks;

are you using water treatments in your system water to prevent corrosion?

I'm interested in how little air is being absorbed into your system from the expansion tanks. I'm still debating what to do for expansion, myself.

 

[RobC]

I will be flushing and treating with what was recommended by (broken link removed) which I found out about from this site. I have 6.5 well water with iron. Between the Tarm and a 5 year old Burnham OB all the piping etc to much $ and time invested.
I sent wood boiler solutions a Email with as much info as I could provide about my system and my water quality and he called back that day and recommended a practical cleaning and treating regiment when I get my system on line. He also said after a couple of months to take a water sample and send to him an he will test to see how we did. What I found to be refreshing was he didn't try to sell me extra stuff and took a minimal, practical approach. With around 1200G total it still adds up.
Rob

 

[RobC]

Air... I'm not an engineer but I don't see how a gas can dissolve and migrate down and up into system. It's not like air in your supply or returns with water rushing past and dissolving. I will be running my tank into the bottom of a Spirovent about 15' away. Leaddog mentioned there is so little disturbance he doesn't have his tank insulated because the hot system water doesn't get to it. This is a good topic because expansion tanks are $...
Rob

 

[sdrobertson]

You fellows using propane tanks (steel tanks without bladders) as expansion tanks;

are you using water treatments in your system water to prevent corrosion?

I'm interested in how little air is being absorbed into your system from the expansion tanks. I'm still debating what to do for expansion, myself.

I ended up buying a case of treatment and treated all of my storage. This is because when I installed my boiler lines to the house, I had a OWB and I put in pex lines that are not O2 barrier. My fear is that I would get small amounts of fresh O2 through those lines as I never could get a good answer on how much O2 would come in through those lines. Next year (isn't that what we always say) I'm going to replace these but I had to get through another year. With the steel tank with no bladder, I don't think that the system absorbs enough O2 from this air to be that concerned about. As stated, the water doesn't move that fast and the air pressure doesn't seem to change but I would certainly like an expert to answer this. What I would do if I was installing it again would be purchase enough treatment to treat as much water as I would have just in the expansion tank. I would hook up the system and fill all the system and then dump in the treatment into the expansion tank.

 

[in hot water]

There is a fitting you might consider for a non bladder expansion or compression tank. It's purpose is to maintain that air bubble in the tank and prevent it from being re-absorbed and vented out. B&G makes them and has a good explanation of the how and whys of expansion tank design and concepts.

It was commonly used in compression tanks, often with a sight glass to "see" the air bubble in the tank. This link will take you to the B&G site.


www.bellgossett.com/homeowners/CompressionTank.htm

hr

 

[RobC]

I had seen these B&G web site has a lot of good info on the how and why of all the boiler parts. The only issue I see with using this valve is it goes to the bottom of the tank. I don't know the weight of a 100 gallon propane tank ( 400 lbs ) but their heavy enough that sitting on a cement floor is a good place for them. As leaddog advised to use the existing propane fill gauge to monitor the water level. I had thought of putting in a sight glass but why not use the existing gauge ? Keep it simple.....
hr... As for the oxygen absorption with the tanks on the ground whats your opinion ? Is the dissolved O2 a potential for system rust? A couple of these tanks have been in use for a couple of years and they haven't had to be adjusted. To me that says there isn't much O2 be absorbed. I was planning on putting my 1/2" expansion line from tank bottom to bottom of Spirovent, about 15" away, or I could go straight up to cieling above tank 7.5' to the 1000G storage tank hot / supply line easier to plumb than up and over to same line where Spirovent is ?
Thanks Rob

 

[Gooserider]

Oxygen only makes up about 21% of the air we breathe, the rest is mostly nitrogen and a touch of other gasses... Nitrogen is essentially inert for our purposes, so the worst case would be for all the oxygen to be absorbed into the water, leaving just the nitrogen which would cause a 2-3psi pressure drop, etc... The O2 would then essentially cause a small amount of corrosion as it gets "locked" into the walls of the ferrous system components. This is not going to be significant, more or less just a thin film of oxidation - small amounts of O2 aren't enough to cause any harm, it's the constant exposure that you would get from regular water replacement or 02 permeable PEX that causes problems.

In practice, while I'd expect SOME O2 absorbtion, I doubt that it would be enough to be noticeable except over a very long period of time.

In terms of tank placement, I don't know the answer, as I lack the "hands on" experience that HR and friends have, but what I'd wonder about is if having a tank that didn't connect to the air vent might not contribute to a loss of air over time... With that B&G fitting, the air separator is part of the connection to the tank, so any air that gets dissolved into the boiler water gets separated out and returned to the tank, maintaining the pressure and volume in it. If the tank wasn't connected back to the air vent, I could see how air might dissolve into the water from the tank, and then later be released by an atmosphere venting air separator - I don't know if this would happen in practice or not... I do vaguely remember that the expansion tank in the house I grew up in was suspended from the ceiling near the boiler (mostly tucked up between two of the ceiling joists) but I don't know if it was for this reason or not.

Gooserider

 

[RobC]

Thanks for the info Gooserider. I started thinking about alternatives to the bladder tank set up over the summer when I was contemplating my storage set up. My first home had the "tank in the joists" that you mentioned, that's what got me thinking about alternatives in the first place. Rob

 

[in hot water]

Well tanks were the same way years ago before bladder tanks. They had a small air admittance device to sip some air into the tank. Of course a well system is a bit different from a hydronic system as you open the faucet and let water out. I imagine the non bladder tank would hold an air bubble for a period of time. With a sight glass, even opaque pex tubing, you could monitor that air bubble.

Lack of sufficient expansion room will just reward you with a seeping relief valve, at worse it pops off some excess pressure. Best to avoid either, as relief valves often fail to reseat after they pop once.

hr

 

[Hansson]

if you are going for the semi open system you can do it like this.
Then you get the cold bottom water to the expansion tank.
The other pipe let out the steam if the boiler starts to boil