70 year old Expansion Tank, oil boiler at 27psi

[Etbrown4]

Perhaps this has been the subject of another post, but here goes...

Have a great working old boiler with the old timey expansion tank, (maybe 10 gal) affixed to the basement ceiling. Pretty sure there's no bladder and possibly no air cushion.

As pictured there's an odd looking elbow fitting just below the tank, and there's a small fitting looking like a schrader valve, however it does not seem to be a shrader.

Probably the tank was not setup correctly by our so called heating mechanic who recently installed a new b&g circ pump, and just refilled the system and likely that tank too, probably incorrectly. That's my guess only based on the resulting 27psi, that we've not seen before.

Can anyone share the steps for properly refilling a typical hot water/radiator system with this old style tank (other than the normal radiator bleeding

 

[Etbrown4]

May have found an explanation for a bladerless exp tank.... Just fill it about half full. Trouble is i see no sight glass to determine when half full.

Here's what I found.

HVAC Expansion Tanks: Plain Steel vs. Bladder-Type

As water is heated, it expands. And, as water is virtually incompressible, that additional volume must be directed to an HVAC expansion tank.

blogs.heattransfersales.com

 

[Sponsor]

 

[Etbrown4]

Any reason I can't turn the boiler off, turn the water feeder off, and drain say 3-4 gal from the bladerless exp tank, and believe that may well solve the pressure problem ?

 

[Fitter30]

It's a b&g atf 12 airtrol fitting. That nut on the bottom has a a very small tube attached to it probably 9-12" long about half the diameter of tank. Your extank is a compression tank and they do get water logged. The small tube could be rusted shut and being 70 years old probably won't get it open but it's worth a try since you been this luckly. Need to shut fill off with a hand warm to cool boiler and a floor drain that works. Could pull the tube ant try to clean it or replace the the tank with a bladder tank which will be smaller in size and maybe relocated. Here's the book on it. Since your not at the relief pressure and winter is over might make it for another few weeks.

https://www.google.com/url?q=https://www.xylem.com/siteassets/brand/bell-amp-gossett/resources/submittal/a-320c.pdf&sa=U&ved=2ahUKEwj-spfF-O39AhWqmmoFHa7yARAQFnoECAIQAg&usg=AOvVaw0H9jKuDgCNMc55n50eOwHv

 

[Etbrown4]

I appreciate the info on the fitting below the expansion tank.

If any forum members saw the pics and great writeup on bladderless tanks, what did you think?

It pictured those tanks as ideally half full. Any reason i can't turn off the boiler and water feeder, and make room in the expansion tank by draining 3 or 4 gallons from the spigot at tank bottom?

Is it reasonable to think it might stay half full, as i am under the impression that water can't displace air in an enclosed tank.

 

[John Gayewski]

I appreciate the info on the fitting below the expansion tank.

If any forum members saw the pics and great writeup on bladderless tanks, what did you think?

It pictured those tanks as ideally half full. Any reason i can't turn off the boiler and water feeder, and make room in the expansion tank by draining 3 or 4 gallons from the spigot at tank bottom?

Is it reasonable to think it might stay half full, as i am under the impression that water can't displace air in an enclosed tank.

I think you would be better off getting a modern expansion tank. It would free up some space and they aren't very expensive.

 

[Etbrown4]

Eventually the boiler will get replaced.

Right now the tp relief valve is relieving between 27 and 30 lbs.

Trying to determine if the mechanic who just replaced the circ pump, did or didn't refill the system properly, and if he should correct an error.

So the burning question is, do the very credible drawings and the detailed description of only half filling a bladerless exp tank, reflect correct procedures which a reasonable tradesman should follow? (if not installing an extrol tank! )

 

[Fitter30]

If that small tube is stopped up air can't enter the tank. If you can drain down the complete system. Can pull that tube and can't unblock it drain tank 100% reiinstall tube tight. Refill system tank will fill at a correct level. Have to get air out through all air bleeds in system. If there are any auto bleeds might want to change them for they might leak from not being used.

 

[Fitter30]

Eventually the boiler will get replaced.

Right now the tp relief valve is relieving between 27 and 30 lbs.

Trying to determine if the mechanic who just replaced the circ pump, did or didn't refill the system properly, and if he should correct an error.

So the burning question is, do the very credible drawings and the detailed description of only half filling a bladerless exp tank, reflect correct procedures which a reasonable tradesman should follow? (if not installing an extrol tank! )

Yes the reinstalled tube can't leak air from threads or the tank will refill in a matter of day or two.

 

[Etbrown4]

I don't plan to take the airtrol fitting apart (shown in the pic) or trying to service it, because it is 70 years old and that type of thing rarely goes well.

So getting back to the excellent article on bladerless exp tanks, it sure seems that i should be able to turn the boiler and water feeder off, and then open the spigot on the underside of the exp tank, and drain maybe 4 gal, leaving it half full of air, and therefore room for expansion. Anybody agree it's worth a try?

Here's the bladerless tank article again, in case you missed it.

HVAC Expansion Tanks: Plain Steel vs. Bladder-Type

As water is heated, it expands. And, as water is virtually incompressible, that additional volume must be directed to an HVAC expansion tank.

blogs.heattransfersales.com

 

[John Gayewski]

Eventually the boiler will get replaced.

Right now the tp relief valve is relieving between 27 and 30 lbs.

Trying to determine if the mechanic who just replaced the circ pump, did or didn't refill the system properly, and if he should correct an error.

So the burning question is, do the very credible drawings and the detailed description of only half filling a bladerless exp tank, reflect correct procedures which a reasonable tradesman should follow? (if not installing an extrol tank! )

Yeah it's worth a try. I wouldn't count on it lasting.


You don't need to wait for the system to be replaced to get a different expansion tank. Theres really no reason not to.

 

[Fitter30]

First water pressure = 2.31' per lb. Say ex tank is 7' from bottom of boiler to top of tank = 3lbs that why system has to be be drain down to 2lbs to get air into tank by tank drain valve. Going to drain it that low drain the rest out of it. Regardless could be fighting air in system for awhile.
So any pressure in system when ex tank drain valve is open how will air get into tank? After the main pressure blows out then air will suck in and more water runs out. If there was a valve in the ex tank line could just close it and open ex tank drain then after it drains reopen valve feeding it.