Dust Collection

  • Advertise with us

« back to Safety in the Woodworking Shop forum

Forum topic by TVC posted 12-16-2020 01:46 PM 587 views 0 times favorited 11 replies Add to Favorites Watch
View TVC's profile


6 posts in 391 days

12-16-2020 01:46 PM

Topic tags/keywords: dust dust collection pvc pipe tapered pvc

I’m in the process of building my dust collection system. I’ve been reading a fair amount of Bill Pentz’s material. I’m going with 6” PVC pipe. Here’s my (potential) problem. I’m also using a Super Dust Deputy. It has a 5” inlet and 6” outlet. I need to hook up the 6” PVC to the 5” inlet. But, most couplings look like they’ll choke the airflow. I’m thinking a tapered piece of PVC would help, gradually moving the air from 6” diameter to 5” inlet. I’m thinking of cutting a long V on opposite sides of a piece of 6” pipe and pulling together (gluing of course) the piece creating a taper down to 5”. Thoughts? Will it preserve most, of not all, of the airflow that a 6” pipe gives?

11 replies so far

View Madmark2's profile


3149 posts in 1868 days

#1 posted 12-16-2020 01:56 PM

No. 5” and 6” pipes have different flows. 5” will never have the same flow as 6” for a given static pressure. As a chain is only as strong as it’s weakest link, air flow is limited to the smallest diameter.

-- The hump with the stump and the pump!

View TVC's profile


6 posts in 391 days

#2 posted 12-16-2020 02:00 PM

Do you think the taper will help at all? I’m wondering if a long taper would ease the flow in transitioning to the 5”.

View Fred Hargis's profile

Fred Hargis

7283 posts in 3773 days

#3 posted 12-16-2020 02:45 PM

The taper will smooth the flow, versus a step down adapter. But you will still be limited by the 5” inlet on the cyclone.

-- Our village hasn't lost it's idiot, he was elected to congress.

View Robert's profile


4782 posts in 2760 days

#4 posted 12-16-2020 02:54 PM

DC is like sharpening on ww’ing forums – many approaches, all achieving the same result. That said, yeah there are some basics to DC, but overall, having done 3 iterations/remodels I’ll tell you I’ve had systems that in retrospect shouldn’t have worked very well but they worked.

To your question, that close to the cyclone, IMO it probably doesn’t matter that much, but it wouldn’t be that hard to fabricate a tapered cone out of sheet metal. Like a lot of guys, I used a 5×6 tapered HVAC adapter.

All I know is, it works fine.

I wouldn’t worry about it & focus on duct layout and fittings.

-- Everything is a prototype thats why its one of a kind!!

View Njner's profile


55 posts in 1900 days

#5 posted 12-16-2020 02:58 PM

With fixed CFM, air velocity will be 44% slower on the 6” side vs the 5” side. For example, a DC that produces 1000 CFM will move the air at 5,092 ft/min through the 6” ducting but will travel at 7,333 ft/min through the 5” ducting. Both of those would be sufficient to move the dust through the ductwork at that CFM as you should target 3,500-4,000 ft/min. This is what is needed for vertical lift of the dust (air moving faster than the dust is falling). However, if you’re only getting 500 CFM, then the 5” would be sufficient, but the 6” would not. Keep in mind this is calculated off actual CFM not DC rated CFM and the drop in rates due to drag from the ductwork. Also, there’s a chance of plugging off going from a large diameter to a smaller one.

View clagwell's profile


392 posts in 1072 days

#6 posted 12-16-2020 05:07 PM

Do you think the taper will help at all? I m wondering if a long taper would ease the flow in transitioning to the 5”.


The long taper will reduce the excess pressure loss at the contraction. It’s not going to be enough to notice. Assuming you have a typical “2HP” DC with a 12” fan you’ll see less than a 1% increase in flow at 500CFM or so compared to an abrupt change in diameter .

-- Dave, Tippecanoe County, IN --- Is there a corollary to Beranek.s Law that applies to dust collection?

View xedos's profile


447 posts in 580 days

#7 posted 12-16-2020 07:05 PM

I think you’re stuck (pactically speaking) with using 5” pipe.

That’s what your cyclone was designed and optimized for. It would have a 6” inlet if the engineers had deemed it appropriate.

View TVC's profile


6 posts in 391 days

#8 posted 12-16-2020 07:14 PM

Thanks folks for all the replies.

View ibewjon's profile


2677 posts in 4073 days

#9 posted 12-16-2020 08:17 PM

I would use 5” steel snaplok duct, 26 guage or heavier. About the same price as pvc. A dust collection taper is longer than a heat duct taped. Oneida sells both. Call Oneida, ask them about your 5/6” conversion.

View fivecodys's profile


1764 posts in 2916 days

#10 posted 12-16-2020 10:45 PM

I called Onieda when planning out my small system. They were very helpful. I would call them and explain what you are trying to do and the issues you have forseen.

-- A bad day woodworking is still better than a good day working.

View TVC's profile


6 posts in 391 days

#11 posted 12-17-2020 12:16 AM

You guys are great. Thanks for all your helpful comments.

Have your say...

You must be signed in to reply.

DISCLAIMER: Any posts on LJ are posted by individuals acting in their own right and do not necessarily reflect the views of LJ. LJ will not be held liable for the actions of any user.

Latest Projects | Latest Blog Entries | Latest Forum Topics