expansion tank woes?

todd_6

I have a brand new radiant system, with a 50 gal expansion tank(5gal). Before firing the boiler, normal pressure is about 12 lbs. After firing when the system gets hot, pressure goes over 22lbs. I am assuming that my expansion tank is too small. If necessary, can I just add another 5 gal beside the one I have? Air bladder pressure is 12lbs. Any thoughts?

Mark Eatherton1

So long as you don't get to

27 PSI, I wouldn't lose any sleep over it. I'm assuming your pressure releif valve would begin releiving itself at 30 PSI.

If need be, you COULD add additional expansion tanks. Just be sure they both connect to the system at the same point.

Keep an eye on it, and if it doesn't approach 27 PSI when it's EXTREMELY cold outside, spend your thoughts on something else...

ME

S Davis

Expansion Tank

When you checked the pressure on your tank did you take the pressure off the system side?

S Davis

Apex Radiant Heating

Sweet

Exp tank

Have found that at over 5000 ft altitude which is where Im located exp. tank out of box is minimum 5 psi over name plate pre charge 12psi. Dont know if this is coincidence or elevation. But I check pressure on all new tanks.

zeke

I have calculated the expansion of water from 70 to 140 degrees and it's about a 1% increase in volume. If that's the case your 50 gal should increase 0.5 gal which should increase your 12psi initial pressure in the 5 gal exp tank by;
5.5/5*(30) or about 3psi. If you conservatively assume an additional piping volume of say 50 gal then I get an increase of 6psi. I don't understand the huge difference unless the 12 psi is not accurate.

todd_6

pressure tank

Yes, I drained water pressure down below to 0 on the boiler gauge, then went and checked the pressure valve on the bladder tank with a gauge. I then fill the system thru the pressure reducing valve which is set to 12psi. After running the system circulator and ensuring all air has been purged with the boiler pressure gauge measuring 12psi, I fire the boiler. When the boiler reaches 170' the pressure is about 22psi or so.

todd_6

further observation

After watching the system a bit more, I noticed some air bleeding off the system on occasion. If there is still excess air in the system, do you suppose that is causing the high pressure when heated to 170'?

lchmb

generally

After filling most system's and heating them to 180 I find that most system's end up in the area of 20-22 lbs....sound's like your fine to me. Just because the tank is set to 12lbs does not mean it will keep the system there...as long as you stay below 27-30lbs...

Weezbo

how many gallons of fluid in the system?