Recommended duct size

[Patrick Curry]

http://www.freecalc.com/ductloss.htm

Why don't you play with the calculator above with what if scenarios? Try with 6" all the way and then with 8" and see what the losses are. Use Larry's 1,200 cfm (or even 1,000 cfm with the short cone cyclone) as it is much closer to what the impeller will produce. You'll get better performance if you can vent outside without filters, subject to proximity of the neighbours.

Thanks Peter. I took it for a spin but may need to spend some more time to understand all those fields. I entered 6” diameter and 1200 cfm....looks like I’m losing 8.9” of water.

[Patrick Curry]

Costs tend to raise my expectations.
I’m $375 ish into the unit. $200 for the Teco 510 VFD which just arrived. I still need to purchase the cartridge filters- $450 for the pair of Wynns. Plus the ducts, elbows, blast gates etc...

To future you reading this...just cough up the $1500 for decent new cyclone and be done with it.

[Joe Jensen]

Here is a post from this forum of an article I wrote on dust collection. If you do the math, the impact on CFM of 8" duct versus 6" duct is negligible. The actual port open at the blade where you are trying to collect the dust BY FAR the biggest impact. Take a look at the PDFs I posted.

[Patrick Curry]

Here is a post from this forum of an article I wrote on dust collection. If you do the math, the impact on CFM of 8" duct versus 6" duct is negligible. The actual port open at the blade where you are trying to collect the dust BY FAR the biggest impact. Take a look at the PDFs I posted.

Joe, did your post this morning include the article? I didn't see it but am interested in reading more.

[Ole Anderson]

7" for horizontal runs and 6" for vertical runs seems to be the sweet spot between minimum velocity and friction losses due to excessive velocity. 800 cfm is a common flow needed to a TS with top and bottom collection. 800 cfm in a 7" pipe is 2993 fpm which is adequate to keep dust and chips moving in horizontal runs. That same flow in a 6" pipe gives a velocity of 4074 fpm enough to move dust and chips up a vertical run, even small off cuts from experience. Higher velocities will of course move even heavier stuff, but at the expense of needing more horsepower to do it, so you can go with 6" as long as you have at least 3 hp IMO. I used a 7" snaplock main with my 2 HP Oneida Dust Gorilla and get some pretty good flow numbers. Numbers taken from the Bill Pentz Static Calculator. If you haven't opened up that spreadsheet yet, it is full of interesting information and opinions, some of them somewhat contradictory, so you have to take a lot of his statements with a grain of salt.

And good luck finding 7" in PVC.

http://www.billpentz.com/woodworking/cyclone/index.cfm go to the Ducting tab, then the Static Calculator Spreadsheet (Excel)

[Joe Jensen]

Originally Posted by David Kumm
I think it is an error to discuss any dust system in terms of 2.5" ports. For those a vac works best. A radial impeller with some speed control still needs larger gates to justify their benefits. I run machines from small 8" jointers with a 4" port to 16" jointers, 24" planers, and big shapers, many old iron. Runs are up to 50' long and have 25 gates. The impeller and filters are remote from the cyclone so there is resistance on both sides of the blower. A curved impeller, even at 17" diameter would not pull the cfm through an 8" reduced to a 7" pipe located 50 ft away to handle my old large machines to my satisfaction. A 15.75" radial not only gave me more cfm in that scenario but pulls 800+ cfm through a 4" port. The cost is that cfm per amp is lower so a 7.5 hp motor is needed. My shaper now gets 2200 cfm at 60 hz and I vary the speed from 55-65 hz depending on what I need. Not an answer for everyone, but there are times when a typical curved blade system won't handle a wide range of machine sizes. Dave



David, the language I used regarding the 2.5" port was referring to the effective cross sectional area of that opening. Take my Felder sliding saw. It has a 5" port on the back of the machine. Inside it connects directly to a 4" flex hose. That 4" flex hose connects to the cast iron blade guard which has an oval opening with an effective cross sectional area of a 3.25" diameter round port. Most machines have a smaller opening at the point of dust generation than the port on the back of the machine.

I broke the paper into small enough files to upload.

Attached Files

• Dust collection optimization part 1.pdf (132.5 KB, 93 views)
• Dust collection optimization part 3.pdf (76.8 KB, 47 views)
• Dust collection optimization part 2.pdf (92.0 KB, 41 views)
• Dust collection optimization part 5.pdf (81.1 KB, 40 views)
• Dust collection optimization part 4.pdf (82.5 KB, 45 views)

[Ole Anderson]

I broke the paper into small enough files to upload.

I have a 2 hp SDG. With the 5" bottom and 3" top (Shark guard) on my TS open I am seeing 5.2" on my suction gauge (Magnahelic) just prior to the DC inlet. Per the fan curve that is just about 1000 cfm. Something isn't adding up with the numbers you are coming up with in the static calculator. My 5" bottom is about 8 feet of 6" steel, 3 feet of 5" flex, a short section of 7" steel, a few fittings and a short section of 7" alum flex into the DC. I have checked the fan curve with a Velicitor air flow meter and it seems pretty close at several data points.

[Bill Adamsen]

Reading Bill Pentz' web-site (Ole provided link above) will give some good background. One objective is to generate velocities that permit catching and moving the type of debris being generated from each machine. Being a one or two open gate shop makes it easier to calculate. For your horizontal runs you want enough velocity to avoid having debris settle (which includes having drops "off the side" – versus bottom – to assist with that goal) and of course you want enough volume to provide the higher velocities required to lift dust in the vertical drops. Most find 7" or 8" horizontals, 6" verticals and 5" port/feeds satisfy this formula. But you should use Pentz' spreadsheet to help make that analysis. I did when designing my system a number of years ago (as well as getting advice here from many knowledgeable folks as you are doing) and my system has performed very well. My only regret was not getting a more efficient and powerful cyclone motor and rotor.

[Jim Andrew]

I have a similar 3hp cyclone, and rigged up a way to dump my exhaust outside, except during extreme weather. I find my system fine when sending the air outside, but when using filters it is disappointing. Seems to have about half the flow when using filters.