Steel Compression Tank Q's

Hilly

I believe reading in Dan's books, I cannot remember which one, I am certain I read that steel compression tanks coming off the top of the boiler should be piped in 3/4" piping. Also if I'm not mistaken I also read that you cannot use a compression tank with a micro-bubbler/air seperator/other name without the use of a certain B&G fitting to permit them to both work properly. Did I make all that up or am I correct?

Tinman

3/4" should be the minimum and I have seen the use of an B&G air separator used with a steel tank in B&G's literature.

Tinman

Here are some illustrations from their literature.

aircooled81

pumping away, ill bet thats where you read that.

hot_rod

get your hands on one of these. originally printed in 1977, reprinted in 2011.

I learned a lot about expansion tanks, design sizing, you name it.

It has info on sizing the "heating leg" fin tube to cool the fluid temperature to the tank. I had heard of this, but never seen the math.

It does include a chapter for sizing the Extrol™ system connection line.

On larger systems, under sizing the line can cause premature relief valve discharge if the pipe size to the tank cannot "move" the expanding fluid fast enough, is how I read it.

JUGHNE

If you truly have a steel compression tank which usually looks too big and hangs from the ceiling and is typically old. Then all the air in the system is supposed to end up in it. If you remove air from the system with an auto bleeder system of some sort then eventually that tank becomes water logged and gives you no expansion value. I learned this the hard way.

That tank should be maybe 2/3 water and 1/3 air. If you have auto air bleeders you end up with all water and the PRV opening.
Even leaking sight glass (if you have one) gaskets on the air side will waterlog your tank.

You use some form of air separator to put the air into the tank not an air eliminator which will remove all the air from the system.

hot_rod

I have never tried it, but could a tube from a microbubbler air eliminator be routed up to the fitting in the tank?

Really the best option is to replace the tank with a diaphragm style, generally about 1/3 the size.

Then the whole issue of maintaining that trapped air bubble goes away, along with all the heatloss from that large tank when heated and expanded water goes into it.

The Amtrol book talks about this skin loss and how insulating the tank would drive up the air temperature inside and limit the expansion capacity "Charles' Law Effect"

Gordy

B&G airtrol tank fitting done. I have a steel compression tank no issues. It is actually quite nice to savor old technology that still does its intended purpose, and works well. K.I.S.S.

And yes no air removal devices with a steel compression tank.