Dust Extraction Piping

bateau · 28 Mar 2021

New to the forum but not new to woodworking. I have just about completed a new workshop. It is 8.4m x 4.2m wide with high cathedral ceilings and a mezzanine floor for my office. It's a nice solid shed, insulted well with a small Norwegian cabin stove to keep warm. Setting up the dust extraction system is the next job and the reason for this thread. I purchased an Oneida Dust Deputy XL cyclone. To the cyclone I will mount horizontally above a 3HP dust fan (i-Tech rubbish). I will cooper (West system boat building technique) a large cylinder holding the dust fan and cyclone so I can make it near sound proof and attached to the back wall of my workshop. The vent from the dust extractor will pipe back into a similar coopered cylinder containing a pair of pleated filters with a dust tray at the bottom and then piped back into the workshop so the dust extractor filter the air and puts it back into the workshop and stay warm.

Just wanted to set the context. I purchased a stack of metal ducting (Nordfab style) which clips together for a previous workshop and didnt complete the system so I have some tubing, bends, branches and clips to reuse. I can see a mistake when I purchased the previous tubing as it's 160mm and not 150mm as I thought. The Oneida cyclone takes 150mm tube into the cyclone and 150mm from the cyclone into the fan and hence the 3 HP fan. As you may see I have a 160mm inside diameter tube being sucked by a 142mm inside diameter from the cyclone which is a 10% reduction in air capacity so my concern becomes air speed. The 160mm tube that runs into the cyclone is at least 1m straight before there is a 30 degree branch that then slowly runs off at 90 degrees to the straight pipe. The straight 160mm tube then continues straight for another 2m before there is a 160mm to 125mm reducer with a 100mm 30 degree branch. I dont have concern for this run as that is such a nice straight run of 3m before reductions to machines and its straight into the cyclone with no bends. The second run that branches off 1m from the cyclone has a slow bend to 90 degrees and then 3.5m straight before another 90degree bend and then runs 3m along a wall in the shop with various machines connected.

So from the cyclone there is a 1m straight pipe in 160mm tube before a 90 degree bend into 3.5m straight of either 140mm, 150mm or 160mm (size to be determined) tube before a 90 degree bend and then 1m to a branch with a 100mm drop and then another 1-2m straight to the 90 degree drop at the end. The end of the line has that 90 degree bend to a 1m drop that has a 125mm blast gate to a branch that has a pair of 100mm tubes for the band saw. The band saw needs 2 x 100mm tubes and because the dust is finer it needs better air speed to remove.

So from the cyclone to the band saw branch (in metal) there is 9m of run with 2 x 90 degree bends before the 90degree end with a 1m drop to the branch. This branch comes off the 160mm tube but I can choose the pipe sizes to help airspeed. The end must be at least 125mm for the 2 x 100mm tubes (about the same flow 1 x 125mm single or 2 x 100mm). So here come the questions. If you dont know thats ok but I was hoping to find someone with some experience.

Do I reduce from 160mm to 150mm from the branch to the first branch or should I Just stay with 160mm? (Am I being OCD?)

I think my plan is to run the 4m from the main branch to the first smaller branch in larger pipe (either 150mm or 160mm) and then possibly reduce from (either 150mm or 160mm) to 125mm with a 100mm 30degree branch drop. Does that sound right?

That 3m run from that first branch into the bandsaw branch of 2 x 100mm. Would you run 160mm all the way to the bandsaw branch rather than reduce to 125mm at the first branch?

I hope these questions make sense and thanks for your input.

Old.bodger · 28 Mar 2021

It's a nice solid shed, insulted well with a small Norwegian cabin stove to keep warm.

Sounds nice so don’t be too hard on it!!!

To address your questions.......I would tend to ‘stay large’ where ever possible and do the reductions at the point nearest to the machines.
Not that I have any expertise, just a gut feeling.

Any pictures to encourage workshop envy?

Inspector · 28 Mar 2021

Welcome to the forum. I had to look up where Barby is. A Canadian answering a guy in France about a Norwegian Workshop building on a British forum.

I played with a duct loss calculator to see what the difference between the 150mm and 160mm duct would be. Now I will switch to North American conventions (the calculator is imperial only) rather than metric so you'll have to do the conversions if you need them to relate. I used 5.9" for the 150mm and 6.3" for the 160mm. Not dead on but close. The calculator is On-Line Duct Friction Loss should you want to play with it yourself. Another useful document has loss figures in feet of straight duct. It illustrates nicely the losses of each kind of fitting starting about page 54. http://www.lorencook.com/PDFs/Catalogs/Cookbook_Catalog.pdf

5.9" galvanized steel duct, airflow of 1,200 CFM (approximate max of 6" duct), 30 ft long, 3 of 90ºelbows of 2R.
The important numbers are 4.15" static pressure loss (measured as inches water column) at a velocity of 6323ft/min.
Going back and only changing the diameter to 6.3" the calculation is 3.006" static pressure loss and a velocity of 5546ft/min.

The important news for you is that the bigger duct will have a 25% less static pressure loss than the smaller duct. This is important as it leaves you more suction to overcome other losses like the cyclone. The drop in velocity is not a problem since the recommended minimum air speed to keep sawdust in suspension is about 4,000ft/min in horizontal ducts and 4,500ft/min in a vertical duct. You have ample to spare. I have never actually seen any measured numbers for the static losses a Dust Deputy XL has. Cyclones add from just over 2" for a very efficient one to over 5" on a poor design. Since your impeller may pull about a maximum 12" with the opening blocked off and about 4" or 5" wide open (both ends of at the fan curve if you have it) any static pressure not lost leaves more to remove the dust. So best to run all ducting as 160mm with no reductions and open the machines to allow the airflow to pickup and transport the dust.

For a bandsaw the best arrangement I have seen is the 6" duct reduced to three 4" ducts in stages not a 3 way wye fitting, less turbulence. One 4" duct under the table at the guides, second into the bottom of the lower wheel guards and the third above the table behind the upper guides.

Sound proofing is best done with several layers of different densities and a baffled or tortured path (zig zag) for the air return. While the coopered housings would look cool the solid sides will resonate and may not reduce the noise as it will be reflected inside and through the walls. More of a closet would be better. In order from inside to outside. Sheets of MDF/OSB/Drywall sealed around the edges, attached to resilient channel (Z shaped metal strips to break the vibration connection of the frame use in drywall installs). 2"x2", 3" or 4"or equivalent studs, followed by resilient channel, with MDF/OSB/Drywall on the outside. The cavities filled with mineral wool batts. The access door being made the same with rubber/foam seals. Sound is contained and absorbed. The air returning back to the room through a sheet goods box, zig zagging through a dense foam rubber / mineral wool held with wire mesh lined maze, path sectional area of 3 times the inlet area. That area would be pi x 80mm x 80mm x 3 = 60,200sq/mm if I remember my math properly. That folding of sound several times absorbs the energy to the point where you should be easily be able to carry on a conversation with someone beside it. The air rushing into the ducting at the machines will be louder.

If you haven't already read it, Bill Pentz has a lengthy, hard to read, useful site on dust collection. Dust Collection Research - Home

Not a professional but I have read and gathered information for years.
Pete

Jacob · 28 Mar 2021

I keep it simple with just one 100mm flexi pipewhich I trail over the floor and connect to whichever machine I happen to be using. No branches, no plumbing, except a 2m length of 100mm drain pipe which I can add with a bit more flexi pipe if I want to go further. Connections all push fit and quick to rig up. Very simple and very efficient.
I've also got a Trend T30 with a long 36mm hose for hand electric machines and general vacuuming.
I've read some of the techy stuff about dust extraction but it might as well be medieval alchemy as far as I'm concerned!
Noisy, but I take my hearing aids out and wear ear muffs.
Timber not good for sound reduction unless damped for vibration. I recently demolished a 60 year old enclosure for a large chapel organ electric wind machine. It was all doubled up panelling with saw dust infill between. Don't know how effective it was but I guess it would have been. Cleverly done - looked like normal frame and panel work with nothing to show that the panels were doubled up.

MikeK · 28 Mar 2021

Pete's information is spot on. I have 120mm steel ducting in my shop and will be upgrading it to 160mm for the main distribution from the cyclone to the point immediately at the machine connection. There's no sense hampering your system by using 100mm ducting except where absolutely necessary to make a connection to the machine. Bill Pentz's information is worth reading if you have time and a few spare gray cells.