Pipe size for vacuum?

[Martin Wasner]

One of the last things I need to set up in the new shop is the dust collection for the three assembly benches. The saws are easy. I bought an Oneida dust Cobra a couple of years ago to do on my dovetailer since the system in the old shop was over taxed already. It's not currently doing anything and I thought it would be a good option for the random orbit sanders on the benches. So just the finest of material will be picked up by it.

I'm planning on plumbing everything with pvc for this.

Am I correct in thinking 2" would be a good size for this application?

Is there any reason to go smaller or larger?

Ball park guess, and likely over estimating, the longest run will have about 60' of pipe. The shortest will have about 15'.

[Robert Cherry]

That's a fairly high performance unit for the size, but I think it will have a hard time overcoming the pressure drop of 60' of 2" pipe. It has a 2-1/2" inlet, I wouldn't go smaller than that. Can you move the D.C. Closer to the action to shorten the pipe runs'?

[Martin Wasner]

That's a fairly high performance unit for the size, but I think it will have a hard time overcoming the pressure drop of 60' of 2" pipe. It has a 2-1/2" inlet, I wouldn't go smaller than that. Can you move the D.C. Closer to the action to shorten the pipe runs'?

Not really a way to shorten up the lengths.
The benches are as close together as they can feasibly be. There's probably 12' of pipe before it even gets out of the bench. Then going up 9' past the top of the bench to get to the ceiling. Then the horizontal runs. I was planning on hanging spiral pipe for the saws and just zip tying the pvc to it where I can.

I am planning on putting the vacuum itself 10' or 12' off the floor to shorten things up as much as possible there. Same with dust collector.

[Jim Becker]

For smaller tool extraction, that unit should perform well, but distance is still your enemy. The Dust Cobra is well suited to the task, but closer to the work is a better choice. I wouldn't break down the duct to the small hose until close to the bench, too.

[Martin Wasner]

For smaller tool extraction, that unit should perform well, but distance is still your enemy. The Dust Cobra is well suited to the task, but closer to the work is a better choice. I wouldn't break down the duct to the small hose until close to the bench, too.

I was planning on running the 2" pipe right to where the hose will connect.

[jack duren]

I went 50ft on a ridgid vacuum and didn't lose anything, works fine on the Domino.. Reduced to 1.25 at the beginning of 50f....

[John Kee]

Just looked up the unit you have Martin and its says you can run up to 100', I would assume by the specs, 2 1/2" for the inlet would be ideal then step down closer the machine. A very interesting shop vac/DC solution I've never heard any mention of on forums. Thanx

[Martin Wasner]

Just looked up the unit you have Martin and its says you can run up to 100', I would assume by the specs, 2 1/2" for the inlet would be ideal then step down closer the machine. A very interesting shop vac/DC solution I've never heard any mention of on forums. Thanx

Yes, I figured I'd run the full size up until I start branching it off.

As a dust collector, in the traditional sense, the Dust Cobra is borderline worthless. It didn't work well on the dovetailer, and it doesn't work well on a chop saw pulling from a well beneath it

I had a 4" line going to the chop box on the bench in the old shop, I think I'm going to up that to 6" on the new benches and pick up a 5hp cyclone to service all three. It'll be a little short if all three are needing suction, but should be fine with two. Nothing works well on a chop saw except for moving a ton of air. With automated gates it should be Pretty awesome. Especially since the saws don't have momentary switches.

I didn't plumb the benches into the main dust collector because it makes zero sense to have a 20hp dust collector running for the sporadic/momentary use of a 3hp chop saw. I think I'm also about at the limit of my baghouse performance.

[Andrew Seemann]

If you've got a 2 1/2 inlet and want to go PVC, 3" Schedule 40 PVC sounds like it would probably do the trick. The increase in size probably isn't so big that you would loose enough velocity to drop the dust on the horizontals, and it is going to have a much smaller SP drop than 2 inch. Plus it is easily available, since it is a common plumbing size, and they make lots of fittings for it. Putting in some clean outs wouldn't hurt.

That said, it probably would be a good idea to do the math to make sure whatever you are going to put in works before spending the time and money.

[Jim Becker]

If you've got a 2 1/2 inlet and want to go PVC, 3" Schedule 40 PVC sounds like it would probably do the trick.
Martin has a commercial shop...and the friendly OSHA folks have opinions on materials that can be used for plumbing dust collection, air, etc. He may or may not be able to execute on that suggestion. :)

[Dan Friedrichs]

Why can't you just use 4" (or bigger), and drastically reduce any friction losses in the pipe? "Oversizing" the pipe won't hurt anything, in this application, since you're only moving fines, so there's little risk of heavier material settling in horizontal runs (or failing to make it all the way up a vertical rise).

[Mike Chalmers]

Nothing really to add here, but some real life observations to share. Over the holidays, I installed a 2 1/2" "central vac" system, using two large Ridgid machines (a 6 and a 6.5 hp) each pulling through a Dust Deputy before combining for the system. Longest draw would be around 35'. I have my router table and my over head table saw collector permanently connected, with 4 drops around the shop and one in my finishing room. I am truly impressed with the performance. Unscientifically, I am measuring around 270 CFM at the strongest gate, which is pretty good for a vacuum system. As I was building, I tried to use some 2" central vac piping I had laying around. I noticed a significant reduction in air flow, so I bought more 2 1/2". I love the system's performance, the usable space I freed up and the convenience of not pulling around a shop vac/dust deputy cart.

[Tom Bender]

I have the Dust Cobra in a small shop and really like it. I piped it with 3" PVC with 3 drops around the basement so it serves as central vac for the basement and in the shop. Got a rubber connector/reducer to the hose size that works perfectly. Just a twist on the worm clamp moves the hose around and caps slip on the unused connections.