Air-troll fittings and open expansion tanks

Timco

It is in the book 'Pumping Away' by Dan Holohan..

Tim

Big Will

I cant remember if it was in a Dan book

or a magazine article. I read a very thorough explanation of air migration and the need for air-troll fitting to stop it. Were is the question. I am almost sure it was written by Dan though. Any insight would help. Thanks all.

Mike T., Swampeast MO

Air-Trol fittings work on closed compression tanks, not open expansion tanks. More specifically they're used on plain compression tanks (the old style without a bladder).

While it's impossible for a circulator to move water and air in and out of a plain compression tank, gravity can. The relatively cold water in the tank can "fall" into the system to be replaced by relatively warm water from the rest of the system. This often results in a situation whereby the air in the tank migrates into radiator(s). When the air is bled from the rads, system pressure drops and either the auto-fill or a person adds more water to get the pressure back to normal. The air that was supposed to be in the compression tank is not replaced however and a viscious cycle begins whereby air keeps getting trapped in and bled from rads while the compression tank holds less and less air. Eventually you wind up with a waterlogged compression tank--as the system heats pressure will rise too high and the boiler T&P will often start "weeping" or even lift altogether.

The construction of the Air-Trol fitting eliminates the possibility of gravity circulation into and out of the compression tank. The air stays in the tank where it should and (provided there are no leaks) air problems will become only a bad memory.

While not difficult to install, make sure you read and follow the Air-Trol installation and filling instructions. In nearly all cases, both the inner and outer tubes that extend into the tank will have to be cut properly for the diameter of the tank into which it is installed. Following the fill instructions helps ensure that the proper amount of water/air is in the tank from the very beginning. In converted gravity systems you'll probably find air pockets in a radiator or two a few weeks after filling--vent the air once, bring the system back up to pressure and--with the Air-Trol on the old tank--everything should stay perfect until the system has to be drained and re-filled for some reason.