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Posted by Tony Conner on April 05, 2005 at 08:22:01:
In Reply to: Glycol system air bleeders posted by GeneratorGrrl on April 04, 2005 at 14:49:09:
How is the system arranged? It should be boiler outlet, expansion tank, then air separator, then the circ pump, pulling water out of the boiler, through the air separator. This arrangement means that the air separator sees the hottest liquid, at the lowest pressure (the closest to the boiling point), allowing any dissolved gasses to pop out of solution. If you're pumping TOWARD the expansion tank, you can have a situation in which the air vents can pull air into the system. The expansion tank sets the pressure for the system. The circ pump can't increase the tank pressure, but will still move liquid, because the suction pressure falls. If it drops far enough, you can suck air into your system. I know a number of installers who run glycol systems for a couple of weeks until the dissolved air is removed, make sure that the system is up to pressure, then valve-out the air vents simply because on glycol systems they're so prone to leak.
The only other possible source of air is from make-up water. The make-up line should be connected to the short section of pipe between the expansion tank and the system. However, on glycol systems, the make-up should be left off, as gradually adding water due to leaks, or relief valves lifting will dilute the glycol.
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