I need some expansion tank theory help... :-)

hot_rod · September 2003

For the how and why's of the charts, try this link. Siggys new software has a great sizer and volume calculator, very handy.

hot rod

http://www.pmmag.com/CDA/ArticleInformation/features/BNP__Features__Item/0,2379,4067,00.html

jess askey · September 2003

I need some expansion tank theory help... :-)

Firstly, let me say that over the last 5 years I have found that Dan's site, The Wall and The Lost Art of Steam Heating have been the best site for a DIY'er like me. I appreciate all the help everyone and Dan has given me the few times I post my silly questios here.

Also, I still have a free 'antique' ARCO coal fired boiler in working condition in Laramie, WY if anyone wants it!!!

Now to my question...

Im in the process of pouring a hydronically heated slab for my workshop/pinball room. It is 3/4" tubing and I have approximately 300' in my single loop which to my best calculation is 6.8 gallons of water. Operating temps would be from 55 degrees (F) to 125 degrees. So, how do I size my expansion tank. I realize that the expansion depends on my pressure but that is going to be very low I beleive. I could not find a good water thermal expansion equation anywhere. I was looking at this 'hydronic expansion tank' (http://www.zurn.com/operations/wilkins/pdfs/specsheets/wxt-HXT.pdf) but could someone plese chime in and connect the dots for me. I dont' want a 15 liter tank if I only need a 2 liter inline version. Plus I guess Im a bit unsure of how to actually balance an expansion tank (I will read some instructions that I found however for a quick tutorial) but feel free to edumacate me on that too. ;-) thank you again.

jess askey
laramie, WY

John@Reliable_4 · September 2003

Jess, check this site out............

http://www.amtrol.com/website/content.nsf

Big Ed · September 2003

Chart

hope this helps

Arthur · September 2003

Expansion tank

Water expands at 1/22 from cold to hot. ie If you have 22 galls when cold in your system you will have 23 galls when hot.
It's always better to have too large a tank than too small. The static pressure in the tank (system empty) should be the pressure you pump the system up to when cold. Then the diaphragm will dilate as the water expands equaliseing pressure on both sides of the diaphragm. Too much rise in pressure cold to hot is usually a sign of a tank which is 1) too small for the system or 2) The tank has lost it's pressure or 3) The system pressure has been set far too high above the tank pressure resulting in the diaphragm being prematurely distended and unable to take the expansion of the system. With the good quality european tank we use over here I've never seen a diaphragm in a tank go yet if properly installed.

Mark Eatherton1 · September 2003

NZ...

would that be New Zealand???

ME

jess askey · September 2003

Thanks... You guys rock!!!

Thanks for the links, plenty to keep me busy. Anyone have any opinions on the watts inline expansion tanks (seem to take up much less space)...

http://www.plumbingworld.com/expansiontankbywatts.html

Arthur · September 2003

expansion tanks

Yep. That's New Zealand. That paradise in the south pacific just to the east of Australia.
Come down and visit us some time.

Arthur · September 2003

Expansion tanks

The watts expansion system would be aright on an direct domestic hot water system and could be quite an advantage to help absorb water hammer and expansion of a small cylinder, note it has a water expansion value of 1.15 galls which means it would be ok on a cylinder up to about 30 galls. the pre pressure is far too high for a heating system at a prepressure of 40 PSI.
A 30 gall cylinder is going to have an expansion of approx 1.25 galls from cold to hot.
It is obviously designed for a DHWS not a heating system.
Horses for courses.

I need some expansion tank theory help... :-)

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