Where does the positive pressure begin on a Dust Collector?

[SpiderDave]

I have a Shop Fox W1687, 3Hp, 13" impeller, 2800 cfm dust collector. I'm probably not wording this right, but lets pretend I am. Ha! On the inlet lines, if it's not perfectly sealed you'll lose minor flow but at least you won't breath the dust right? Well for the sake of sealing everything up nice and tight, I was wondering where does the positive pressure on a dust collector begin - at the outlet or just before? Around the 13" impeller is the housing with a plate and inlet over that. It's sealed with the usual foam seal between and bolted down all around. Very similar to how the motor is mounted as well. I've always wondered if I should be sealing that for good measure or is that still an area where if there was a leak, the air would be pulled in or pushed out? Seems like the impeller would be forcing air there outward and be pushing on that seal. At what point does the air go for positive to negative pressure? While we're at it, what about all the crimped seams in the body where the sheet metal was joined. would it hurt to seal those up for the same reason? Or is that a waste of time? I don't have it hooked up yet, or I would test it with some smoke and see here it goes. I was hoping someone here might know? Thanks no matter what and have a good one!

[daddo]

On the face of the impeller blades (leading rotation side) especially toward the tips, though there is a degree of cavitation at the tips of any blade. I'm sure there are spots of venturi effects happening inside the housing, but why worry about that unless you have a large opening?
Performance values depends on the quality of the blower motor/vanes/housing design as well as the ducting, type of bags/filters..........clean or dirty, how tight the shop is if you exhaust to the outside..........

[SpiderDave]

On the face of the impeller blades (leading rotation side) especially toward the tips, though there is a degree of cavitation at the tips of any blade. I'm sure there are spots of venturi effects happening inside the housing, but why worry about that unless you have a large opening?  
Performance values depends on the quality of the blower motor/vanes/housing design as well as the ducting, type of bags/filters..........clean or dirty, how tight the shop is if you exhaust to the outside..........

Thanks daddo, that's about what I was assuming. Better to hear it form someone who knows more than me. 

(.... venturi effects happening inside the housing, but why worry about that unless you have a large opening? ) I have some breathing issues to be cautious about but also because I'm considering going with a filter instead of piping it outside. I'd think any kind of filter - especially the more it's used - has some sort of back pressure or resistance? So I was trying to get my head around how tight it would need to be sealed up. I have some peel-able caulking I thought about using. Just in case I ever have to open it up in the future.

If I used it with a filter, I was wondering about the odds of an invisible pin hole of dust would be shooting out into the air. Which if it was leaking, maybe it would clog shut anyway? ha! Either way I go, the room that I work in is separate from the rest of the shop. I'm trying hard not to keep dust confined. I have a question on air filters, but I guess that's gotta be a different thread so I don't go off subject. 

Thanks again!

[jteneyck]

Seal all seams, regardless of on the inlet or outlet side of the fan.  Leakage either way isn't good. 


If you want the cleanest air in your shop and maximum flow from your DC system, duct the exhaust outside.  Filters reduce flow even when new, and get worse as they clog up over time.  A really good cyclone will remove all but the finest fine particles from the air stream and prevent a dust plume outside.  

John

[TDKPE]

If you want the cleanest air in your shop and maximum flow from your DC system, duct the exhaust outside.  Filters reduce flow even when new, and get worse as they clog up over time.  A really good cyclone will remove all but the finest fine particles from the air stream and prevent a dust plume outside. 

What he said.  My Pentz-designed cyclone collects wood flour from sanding.  Super fine stuff.  And I get no visible dust in the snow in the window well where I exhaust the air out the casement window.  So I'm happy with how well it works.  So is my neighbor, who I don't think even knows what that is making that noise in the window toward his garage.  

[daddo]

Mine exhausts straight from the upper bag. I warn people not to park in that spot outside the shop when I'm in the woodworking mode.

[SpiderDave]

Okay, I'll seal every single seam not matter what then. Certainly cant hurt, right? I would like to also just have the cyclone, barrel and pipe it outside also. Seems the best method to me. Thanks for everything!!

[Mike in kc]

...A really good cyclone will remove all but the finest fine particles from the air stream and prevent a dust plume outside...

I agree.    This places all the shop ducting in negative pressure, so there is no "blow out" from the seams. This arrangement also keeps all the big pieces out of your blower which could cause some real damage. Note the BIG SCREEN in your blower, designed to "prevent" same. 

A Cyclone is easy to build should you be so inclined, and, the total cost is less than about 50 bucks, since you already have the blower. Wood Magazine had an article maybe 15+ years ago for making a cyclone, which I built.   I also welded up the blower impeller and built the blower housing.  It's been fifteen years since I built it and its proven to be one of the most useful projects I ever did.

[SpiderDave]

I agree.    This places all the shop ducting in negative pressure, so there is no "blow out" from the seams.   This arrangement also keeps all the big pieces out of your blower which could cause some real damage.   Note the BIG SCREEN in your blower, designed to "prevent" same. 

A Cyclone is easy to build should you be so inclined, and, the total cost is less than about 50 bucks, since you already have the blower.   Wood Magazine had an article maybe 15+ years ago for making a cyclone, which I built.   I also welded up the blower impeller and built the blower housing.  It's been fifteen years since I built it and its proven to be one of the most useful projects I ever did.

Wow, I didn't actually get a quote on the material but I thought it would've been much more than that considering other projects I've done in the past.  I got discouraged trying to get the Bill Pentz equasion or blue prints to build one to proper specs for my set up. I'm more than capable, but attempts to contact them or any other outfit just didn't pan out for me.  A lot of those places are probably so busy, that if you can't figure it out yourself then they don't have time to help you - I'm only assuming.  But if it 's that cheap to build, then I may go round two trying to get the blueprints.  Hmmmm....

[fredhargis]

I also built the Wood cyclone and agree with Mike, I was quite surprised at how cheap it was to build (enjoyable as well, my first attempt at sheet metal work). With the subsequent improvements they published it's a very  serviceable unit. The Pentz design is  a little (maybe a lot) more complicated, but a lot of folks have built one.