PBC damper HELP!!!

[ILikePigButts]

Getting ready to fire up my new PBC and when I went to set the damper at the bottom it seems it doesn't close all the way?! Is this normal?

[MBMorgan]

Yes it's normal. The folks at the PBC company apparently just use the disks they cut from each barrel as the damper. Note that the "hinge (just a little bolt) is a little above the hole and because the damper and hole are almost exactly the same size, it will never quite close correctly. In fact, a fully "closed" PBC damper is really about 1/8th open.

[ILikePigButts]

Thank you so much for the quick response. Figured it wasn't defective but I just wanted to make sure. Makes perfect sense now. Ribs going in soon!

[MBMorgan]

ILikePigButts - Enjoy the ribs!

BTW: what's the altitude where you are?

[ILikePigButts]

MBMorgan about 1100 ft. Got it 1/4 open.

[MBMorgan]

"about 1100 ft. Got it 1/4 open."

Actually, I did a little curve fitting a while back so that I could create an Excel-based calculator to compute slightly more "exact" vent settings for the PBC. It suggests that at 1100 ft., your vent should be more like 3/8 open ... kind of like this:



If 1/4 gives you trouble, you might give this a try ...

[smn1285]

I hate to bother you, but, you’ve posted enough charts to spark my curiosity. I’m (according to google) 390’ above sea level. Where does that land me? 3/16” open?

[MBMorgan]

smn1285 - I’ll check it out when I get back to my desktop tomorrow (Sunday). The PBC vent settings aren’t terribly precise so I’ve chosen to round off to the nearest 8th ... but I’ll check to the nearest 16th for you.

[RobertC]

Over the years I have had to have conversations with aerodyamicists for various reasons, including a couple of side discussions with HVAC experts. I don't think aperture-size is linearly related to flow. (In certain odd cases, it's not even ordinally related to flow). Air can be pretty weird stuff.

[MBMorgan]

smn1285 - The calculator says that (rounded to the nearest 16th) your vent should be 29% ... or approximately 5/16th open. According to the PBC folks, the minimum opening at sea level is 1/4 (4/16th) so it would never less than that.

FWIW, I don't bother with anything smaller than 8th's because the vent setting is rather crude in the first place and, even with the graphic I created to help visualize how it should look, it's still difficult to be accurate.

In your case, it should look a bit like this:



Again, this is just an approximation ...

[smn1285]

MBMorgan awesome, thank you!