\"area\" of no pressure change?

Mark J Strawcutter

Older boiler with built-in air separator (dedicated boiler tapping) and steel (non-bladder) expansion tank. Plan to re-pipe near-boiler and move circ to supply in pumping-away configuration.

What problems, if any, will I create if I add a B&G IAS between the boiler and the circ and pipe both it and the built-in one to the single expansion tank (with airtrol fitting)?

My first thought is that I could have flow out the built-in's pipe and back in thru that of the IAS. While the flow should be negligent/minimal since the regular path thru the boiler has less resistance, it could mess up the flow of air from the IAS to the tank. Wonder if a swing-check in the IAS-to-tank line would help?

Another concern is would I no longer have a "point" of no pressure change but rather an "area" of no pressure change
between the two separators? If so, would this have any nasty side effects.

I've seen multiple expansion tanks in parallel off a single air separator, but never the other way around.

Mark

Steamhead

Mark, is the built-in separator

working as it should? If so, I'd leave it in service. If the existing tank is piped to the separator, it too can stay as it is. If not, pipe it to the separator. Move the circ to the supply line as it leaves the boiler. That should be all you need to do!

Make sure your circ isn't too big (see the sizing charts in Hot Tech Topics), or the increased flow can overwhelm the built-in separator. Ask me how I know that!

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Mark J Strawcutter

I have my suspicions

that the built-in isn't cutting it. Hate to cap it off, have air collect and cause problems in the boiler.

I also considered piping the built-in over to the where the regular supply leaves the boiler. Any air collected would then migrate over to the IAS. Downside is that this would result in a partial "boiler bypass".

Most of my "problem" (air collects in upstairs bath rad, expansion tank waterlogs) is probably due to pumping toward PoNPTC and no airtrol on the tank. Proper piping should take care of things (using built-in separator) but I was trying to hedge my bets and save some re-do work later by adding an IAS.

Mark

Steamhead

If you go with the IAS

> that the built-in isn't cutting it. Hate to cap

> it off, have air collect and cause problems in

> the boiler.

>

> I also considered piping the

> built-in over to the where the regular supply

> leaves the boiler. Any air collected would then

> migrate over to the IAS. Downside is that this

> would result in a partial "boiler

> bypass".

>

> Most of my "problem" (air collects in

> upstairs bath rad, expansion tank waterlogs) is

> probably due to pumping toward PoNPTC and no

> airtrol on the tank. Proper piping should take

> care of things (using built-in separator) but I

> was trying to hedge my bets and save some re-do

> work later by adding an IAS.

>

> Mark





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Steamhead

With proper pipng

Pumping Away, proper circ sizing and an Airtrol, you shouldn't need an IAS. I'm leery of using two separators with that plain steel tank. You definitely don't want to connect them together, and if you put an automatic vent in one of the separators the air won't get routed into the tank.

Of course, you could always switch to a diaphragm-type tank. But I'd try pumping away and an airtrol and maybe re-sizing the circ first- especially if that's a converted gravity system.

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Mike T., Swampeast MO

If you just add an air-trol

and connect the built-in separator to the open tank I believe your air problems will disappear. Mine sure did.