Where can I buy better replacement nouns vent for a supplemental solar heat system? The vents it uses currently work for a 6 inch diameter nouns...

The vents it uses currently work for a 6 inch diameter nouns duct. The vent uses 2 flappers that are controlled by a central, removable bar that turns a screw mechanism to open/close these flappers (metal semicircles ). Unfortunately these flappers be not designed to seal powerfully. Brackets to hold and move these flappers, have not here design holes in the flappers. Also within are other gaps along the straight outskirts on each flapper. There must be more modernized air handling valve !
How do i repair hip bath excess and...
Answers:    the kind of dampers you are looking for do exist, but are vastly expensive. it sounds like you would benefit from some 6" round pipe zoning dampers. try this join
http://www.ewccontrols.com/rounds.htm
these are the zoning dampers that I use when i do a zoned house. you can see in the pic they enjoy a rudder lip on the damper blade. the link explains things better than i really want to, so in attendance u have it.

Possum, HVAC guy