Dust collector system design

[tedrussell]

I'm designing a dust collection system for a new wood shop my son is building in a new makerspace.  He has a 2 hp Delta 50-761.  The plan right now has two 6" horizontal lines - one is a 36' line going to the table saw and chop saw, and the other is a 15' line going to the jointer and planer.  Then there will be 4" drops to the tools.  It will all be with 26 gauge galvanized steel.  I'm making the lines as straight as possible, and using 45 degree bends (not 90) wherever possible. The lines will be 11-12' above the floor (the building is 15' high). Does anyone know this machine enough to tell me if this design sounds adequate?

[fredhargis]

It's always a guess to say whether something like this will work, but that seems to be enough collector for what you want. With a 12" impeller and a 2HP motor, it should draw adequate airOne thing about your design that might bite you in the butt is the 4" drops feeding the 6" trunk line. There needs to be enough air in the 6" to carry the chips/dust, especially across 36'. What i'm queasy about is whether the 4" drops will allow enough air for that to happen.

[tedrussell]

It's always a guess to say whether something like this will work, but that seems to be enough collector for what you want. With a 12" impeller and a 2HP motor, it should draw adequate airOne thing about your design that might bite you in the butt is the 4" drops feeding the 6" trunk line. There needs to be enough air in the 6" to carry the chips/dust, especially across 36'. What i'm queasy about is whether the 4" drops will allow enough air for that to happen.

Thanks.  Do you think I should go with 6" drops? Somewhere I read you need 4,000 ft/min velocity to keep chips and dust suspended.  For 6" drops, that means I'd need at least 800 cfm per line.  If I have two tools operating, the 2,100 cfm total would split into 1,050 per tool, which is enough, but if I have three tools running, it's not enough. For 4" drops, I would only need 350 cfm per drop to keep the 4,000 ft/min velocity.

[Ken Vick]

I'm designing a dust collection system for a new wood shop my son is building in a new makerspace.  He has a 2 hp Delta 50-761.  The plan right now has two 6" horizontal lines - one is a 36' line going to the table saw and chop saw, and the other is a 15' line going to the jointer and planer.  Then there will be 4" drops to the tools.  It will all be with 26 gauge galvanized steel.  I'm making the lines as straight as possible, and using 45 degree bends (not 90) wherever possible. The lines will be 11-12' above the floor (the building is 15' high). Does anyone know this machine enough to tell me if this design sounds adequate?

You are asking a lot from a small dust collector with such long runs and having the ducting that high off floor.  I don't have experience with that particular model but I ran a similar 2HP DC for several years in a more compact shop and had the occasional duct plug up even with much shorter runs particularly from the planer.  This was in a shop with only 1 or 2 gates open at a time.  Since you are talking about shared space, I assume there might be more than one person working in the shop at the same time.  I think that will be trouble, especially keeping sticky planer chips moving through the ducts.  But it might work, I certainly can't predict with certainty, but it would be prudent to optimize everything.  That means 6" drops to the machines including changing out the ports.  Two 4" ducts handle almost as much air as one 6' duct so for machines like drum sanders and some bandsaws, two 4" drops would work.  Move the big chip producers as close to the DC as possible.  I think you would be much happier with a 15 or 16" impeller and a larger motor to spin it.  I know I was and no way would I want to go back to my old DC with ducts plugging up and barely adequate air movement.  Ken

[Ken Vick]

Thanks.  Do you think I should go with 6" drops? Somewhere I read you need 4,000 ft/min velocity to keep chips and dust suspended.  For 6" drops, that means I'd need at least 800 cfm per line.  If I have two tools operating, the 2,100 cfm total would split into 1,050 per tool, which is enough, but if I have three tools running, it's not enough. For 4" drops, I would only need 350 cfm per drop to keep the 4,000 ft/min velocity.

I just read your later post.  My comment is don't believe the CFM data that came with the machine.  They are grossly inflated.  You will be lucky in your real world situation to get 40% of that airflow with long runs and high ceilings you have.  Those factory CFM numbers are collected with no load on the machine and the numbers have been debunked many times by actual measurement of airflow in real world duct systems.  Ken

[tedrussell]

I just read your later post.  My comment is don't believe the CFM data that came with the machine.  They are grossly inflated.  You will be lucky in your real world situation to get 40% of that airflow with long runs and high ceilings you have.  Those factory CFM numbers are collected with no load on the machine and the numbers have been debunked many times by actual measurement of airflow in real world duct systems.  Ken

Thanks, Ken. I understand all that, and I believe you.  I'm a retired mechanical engineer, so I get the principles behind it. What I don't understand is why all the guidelines I have found online for dust system design don't mention vertical height as one of the variables, and why they don't tell you that you need to significantly discount the CFM ratings.  Does anyone know of a better design guide that has ALL the important variables? What about losses as the filters start to get clogged? What about losses from a 4" port on a tool that gets quickly expanded to a 6" vertical line?  What about losses as the main trunk line goes into one of the three 4" inlet ports on the collector? This collector was bought used at a reasonable price, so buying a different, bigger collector will involve significant expense which I'd like to avoid if I can have reasonable confidence that the Delta 2 hp machine can be made to work with an optimized system design.

[TDKPE]

 What about losses as the main trunk line goes into one of the three 4" inlet ports on the collector? 

That’s the first thing you change.  Make your own inlet, 6” or greater, for the trunk line.  

Vertical distance doesn’t really matter, as air has no weight to speak of (gravity head), and if the air speed is enough to hold chips in the flow, then height only counts as far as duct length goes, added to the total, or equivalent total footage, allowing for additional restrictions like elbows and such.

And I agree that you’re asking a lot of a 2 HP DC.  Open things up as much as you can.  Vent outdoors if you can.  Use oversized duct or flex after the blower.  Keep the heavy chip producers close to the machine so you can use a larger duct and still have enough air speed to move things along.

And do monitor the current draw.  It’s easy to overload the motor by not having enough restriction in the ducts and filters when opening things up so it can ‘breathe’.  Adding a long duct run will add a lot of flow resistance, which can be balanced by opening things up for better flow, but you do have to be careful about not letting too much through if you want your motor to last.  

I plopped my 2 hp HFDC on top of my Pentz design cyclone, after opening the inlet up to the same 9” diameter as the outlet of the cyclone separator, and ducting the exhaust out the window with 8” flex.  6” trunk line to 4” taps to various machines, and it draws more current now than when stock, with bags.  I have to be careful not to open more than one set of gates - RAS and lathe have a single 6”, while TS has a 4” with 2-1/2” for over arm, and BS has two 4” ducts.  The RAS and lathe are at the far end of the run, so the resistance is a little higher out there than the other machines, which are closer.

[tedrussell]

Vent outdoors if you can.  Use oversized duct or flex after the blower.  

That's all a big help - thanks.  When you say 'vent outdoors', do you mean send the dust and chips outside instead of into a collection bag?  That's not really an option for this building, for several reasons.

[TDKPE]

My cyclone separator removes nearly everything, so I just blow the exhaust out a casement window.  No sign of dust in the snow in the window well, and lots of wood flour in the bin, so I’m comfortable with just aiming it at the neighbor’s garage.  

[tedrussell]

My cyclone separator removes nearly everything, so I just blow the exhaust out a casement window.  No sign of dust in the snow in the window well, and lots of wood flour in the bin, so I’m comfortable with just aiming it at the neighbor’s garage.  

I'm still learning about all this ... I kept seeing mention of cyclones, and thought they were an alternative to a filtered separator.  Now I realize a cyclone is a pre-separator that is upstream from the separator. Correct?  Contrary to what I said before, if I add an $890 Oneida cyclone to the system, I could probably vent the exhaust out of the building, and I'll have a much better performing system.  The additional expense would be less than a new 3 hp separator. But does the cyclone incur an additional static pressure loss that outweighs the improvements of a cleaner filter and open venting to the outside?