Dust Collector Ductwork -- does this matter?

[Dan Case LR]

I'm putting some final touches on the ductwork design for my new Oneida V3000 and have a portion that I need some objective input on.

ScreenShot039.jpg

This is the end of the ductwork farthest from the cyclone. I'm running 7" mains (brown duct) and 6" drops (yellow duct) in 26ga steel. The port to the far right in the image is a 6" floor sweep. The other 4 drops are for machines that have 4" ports on them that can't be reasonably upsized--13" planer, small drum sander (Jet 10-20), 12" disk sander, etc. I'm using 6" blast gates throughout the shop with a view toward future machine upgrades, and will do the reductions as close to the machines as practical. The run along that wall is lower to accommodate the lumber rack above.

Here's the point I'm waffling on...the "when in doubt, overbuild" engineer in me wants to take the 7" as far as possible, as shown. the "geezelouise this ductwork is expensive" tightwad thinks I should go for "Plan B" -- put a 7-6-6 pants wye right after the 7" 90 that drops down the wall and do the run under the lumber rack in all 6". I'm a one-man garage shop, so the only way (in theory) I'd have more than one gate open at a time is if I forget to close one (and that does happen).

I realize there's a good bit of hair-splitting here and either option would work in my situation, but I'm in what I call a "waffle loop," trying to settle the internal debate. Nothing works better at this point than an objective opinion or three from outside the loop.

So, is there any tangible benefit in running as much in 7" as possible, or is plan B just as functional? I can save a few bucks with plan B--an important thing this far into a project with a swelling price tag--but initial cost isn't my only consideration.

Thanks!

D.

[James Baker SD]

I cannot answer the technical question of which is better for airflow and dust collection. However I did a somewhat similar decision making on my duct layout and ended up using all 7" pipes from a 5hp Oneida, reducing only when I reached the flex hose to the individual machines. My thinking was if I ever re-arrange the shop (one man shop in half of a 2 car garage with 2 cars still parked inside), then having all 7" pieces would maximize my flexibility in reusing the pieces for the new layout. By the time I was finalizing my layout, the budget was so badly blown, I just closed my eyes and pretended it would go away, so the price difference got lost in the noise.

[Wade Lippman]

As I understand it...
Presumably you will only have one line open at a time, and have small machines on a 3hp cyclone. It would probably work if you ran 4" everywhere. The concept of two 4" coming together at a 6" and two 6" coming together at a 7" is only important if you are using several machines to balance the load.

I didn't see all that much difference in cost between the different sizes, and did it properly; 8" to a couple 6", 6" to a couple 4". With my Grizzly 3hp I get plenty of suction even if I forget to close a few blast gates.

My recommendation is to not worry too much about it; it will work whatever you do.

[Jim Andrew]

I looked at your plan, looks like the Y's are turned down with a 45 to complete the 90 degree drop. I had a couple set up like that with my previous setup, and chips would fall down the Y when I had the further gates open. The chips cause a plug when set up that way. A better way to set it up is to position your Y flat, and then turn down with a long sweep 90. If you have a local Ace hardware, check out the cost of their pipe and fittings. I would ask the manager if they can order longer pieces of pipe than the 2' pieces at my local Ace.

[Michael W. Clark]

Its hard to give a difinitive answer, but based on the fact you have a 3HP collector and 4" connection points, I would stay 6". Jim's point above is good in that if you have enough velocity in the duct you are less likely to experience the situation he is referring to. The 4" connection at the machine is determining (the choke point), having a 7" will give you less loss in the 7" section, but you also need more flow to keep up the velocity. Look at it from the perspective of maintaining 3500-4000 FPM in the ductwork.

Mike

[Dan Case LR]

I looked at your plan, looks like the Y's are turned down with a 45 to complete the 90 degree drop. I had a couple set up like that with my previous setup, and chips would fall down the Y when I had the further gates open. The chips cause a plug when set up that way. A better way to set it up is to position your Y flat, and then turn down with a long sweep 90. If you have a local Ace hardware, check out the cost of their pipe and fittings. I would ask the manager if they can order longer pieces of pipe than the 2' pieces at my local Ace.

Jim, I know the downturned wyes are less than ideal. I've had that exact problem with my previous setup, and went to a lot of effort to eliminate downturned wyes in the new setup. Unfortunately, flattening them out and adding an LR90 will force the machines along that side farther from the wall, and I don't want to lose that space if I can avoid it.

Thanks!

D.

[Kent A Bathurst]

So, is there any tangible benefit in running as much in 7" as possible, or is plan B just as functional? I can save a few bucks with plan B--an important thing this far into a project with a swelling price tag--but initial cost isn't my only consideration.

Yes. In general, take the largest dia as far toward the source as you can - either physically or financially.

You're running 3hp - I assume you will have one blast gate open at a time. You aren't going to have a big problem either way. I'd put the big waste generator - planer - closest to the DC if that is possible.

If it was me, I wouldn't break the bank on this topic. But then, its your shop and your money, and I'm in the peanut gallery.

One design note - the plumbing for the floor sweep looks kinda odd to me. Unless I am missing something, I would make that drop right above it from the main horizontal, rather than crossing the shop and reversing course to cover the yardage you already had won.

[Dan Case LR]

One design note - the plumbing for the floor sweep looks kinda odd to me. Unless I am missing something, I would make that drop right above it from the main horizontal, rather than crossing the shop and reversing course to cover the yardage you already had won.

I think the graphic I posted may have given you a wrong idea of the space. The ceiling line drops by about 16 inches just behind where the 7" main runs (which presents all sorts of ductwork design challenges). The floor sweep are on the same wall as the 4 machine ports, but back under the lower ceiling.

D.

[mike mcilroy]

I just set up a Grizzly and I used 8" for 1 section of duct then reduced to 6" for the rest of the system I am with Wade you will have plenty of pull even with mutiple gates open. My worst offender SCMS is fine even with another gates open and leaks everywhere as I am still waiting for some blast gates so I am using crimped end caps hand fit and a few kiity litter plastic lids taped over 6" wye openings.
As far as the down turned wyes just open the others one at a time with the machine on.

[mike mcilroy]

Also if you have clear flex from the drops you'll be able to check it while in use e.g. watch drops between where you're working and the collector.

[Thomas Canfield]

I like to use reducing "Y" fittings for branch and even at end of trunk. One of my concerns for a cyclone is to maintain a sufficient flow of air for the cyclone separator to work and cause the lighter dust to have enough velocity to not be carried out to the fan and final filter. I always have an extra gate open on my 2 HP Oneida cyclone, and try to have it on the larger trunk line to keep velocity up in the larger diameter and also for the cyclone since the trunk is sized for multiple units operating. Higher velocity in the trunk will also help prevent particles dropping out when passing the down turned branch "y"s which are much better than "T" branches.