sizing outlets for air vents-mains and rads

the one i have in hand is a big box Durst A883 with a reputation for short life so i'm installing with blue monsters anti seize tape. not sure where i ended up with this one as I usually purchase from heating distributors but there it is in my vent drawer. this isn't hard to get to and i'll let it serve as test bed. I /can see talk of balancing main venting by ganging number ones or sometimes a 2 but even gorton's literature is vague about the actual comparative rates or orifice sizes of its highly reputed fixed size vents. And to all indications from discussions here a varivalve at max is a wider range than the entire fixed gorton line, although i'm not sure where the actual rates of specs vs. experience retell that.

anyway, wondering if I should drill the 5/64" outlet on this durst out to 3/16 or some such or if the choke point in these vents is the design of the operating parts. I tend to get the sense from the manner in which the adjustables constrain the outlet that you could obtain significantly more venting by increasing the outlet orifice.

this is the single main vent on a small system albeit the main does have two legs and one one leg is counter flow with no main vent while the other branch has a dry return with this vent place just before it drops back to the boiler.

@ChrisJ cause everyone wants an 8 point buck! esp. given that #1s are so much less than #2s, maybe more points is better ;- )

@SteamingatMohawk and @Steamhead thanks for the venting rate links. upon reflection I feel like it is pretty hard not to see the case for just stocking straight and angled varivalves. because the varivalve rad vent is almost twice the capacity of a Gorton #1 main vent. so you could manifold a couple and have the equivalent of a gorton #2 for a third of the price. and you have adjustment capability if you want to balance further. I always liked them, but never considered them for main vent work. but I will now. (and the straight configuration is actually a little higher capacity and lower cost!)

@SteamingatMohawk @ARobertson13

so i think what the note on varivalve is saying is that the venting rate adjuster doesn't provide complete closure but that is a pretty big range. so then the question boils down to the bellows operatin and bellws separation problems mentioned in the "cloggin" thread.

in the NFN department, if the bellows tend to separate and close the orifice by gravity, is therre any reason you don't rotate the unit to face down? then the bellows would be held away from the orifice by gravity but still close when steam gets to the bellows (in contravention of the sellsheet idea that steam never gets to the vent body ;- )

it's disappointing that folks have had trouble getting reliable operation out of these valves that would otherwise offer a wide range of venting rate for stocking a single unit. I have had these on rads before but didn't realize their theoretical range as compared to other standard adjustables.

they are a nice heavy little puck, and seem like a good idea to me and they have been around the block. but they don't seem to get high marks for reliability or manufacturer's responsiveness. i'm going to tiptoe into their use rather than fill the bin and report results.

brian

PS - besides the reference chart posted here at heating help, i thought someone had put in a link to a long list of venting rates of different manufacturers. but i can't find that link in the thread here. maybe it was in one of the threads i jumped to?