[OP]
Contributor
I'm in the process of extending my dust collection to a Powermatic dual drum sander that has 2 - 4" exhaust ports. I plan to come off of an 8" main that is fairly close to the Oneida venturi type dust collector with either a 6" or 5" branch, then to a wye fitting that has 2 - 4" ports. A 6" branch would obviously carry more volume than the 2 - 4" ports or 5" branch but with less velocity. Would the 5" branch be better considering the greater velocity?
Last edited by Steve Mathews; 08-08-2022 at 1:16 PM.
Contributor
A 5" duct will only carry 1.56 times the amount of CFM of a 4", so it is not recommended if you have a 2x4 wye branch. A 6" branch will carry 2.24 times the CFM of a 4". If you run a 5" drop, you will be starving the two 4" ports from the sanding machine.
If you're dust collector is strong enough to pull air through a horizontal 8" main, then I believe a 6" drop should be fine.
Last edited by Aaron Inami; 08-08-2022 at 1:27 PM.
[OP]
Contributor
Starving the two 4" ports is what I thought might be beneficial but was thinking more in terms of increased velocity in the branch. It's my understanding that velocity and CFM are both to be considered in achieving a good dust collection system. Maybe velocity isn't as important in this situation where fine dust particles are being moved instead of heavier wood chips.Originally Posted by Aaron Inami
Contributor
I think it really depends on how strong your dust collector is. With 8" main, I would think you need at least a 15" impeller (but a 16" is likely recommended with 5HP motor). An 8" main is a really big main. If you do a 5" drop and that's the only blast gate that is open, it is likely that you have enough velocity to pull dust up the 5", but you may not have enough to move dust horizontally in the 8", unless you have a second drop blast gate open at the same time.
So I think it depends on the power of your dust collector impeller/motor and how many blast gates you have open. Sure, you can starve the two 4", but it may not pull enough dust from the sander.
Based on my reading, the goal is to have enough velocity to pull the dust up the vertical drop. The main is commonly going to be larger and the velocity slows down with a larger main, but it's less difficult to pull dust horizontally through the main than it is to pull vertically up the drop.
A 5" drop has good velocity, but may not provide enough CFM to give adequate velocity for an 8" main (which is why I was recommending to have two drop blast gates open if you use a 5" drop to a 8" main).
At least, that's my understanding.
Last edited by Aaron Inami; 08-08-2022 at 2:48 PM.
[OP]
Contributor
The Oneida DC looks like this one ... https://www.oneida-air.com/dust-coll...dust-collector but has a 3hp motor. The inlet is 8", which is the reason for an 8" main before reducing to 6" as recommended by Oneida. The branches are 5" and 4" depending on the machine it's connected to. The larger going to a 12" jointer and 20" planer. I'm having a hard time seeing something larger than 5" feeding the sander but I suppose it won't hurt using 6" instead. I'll try to post a pic a little later if it helps. BTW, I'm the only user in the shop so only one blastgate is open at a time and all machines have them.
Moderator
No question, I'd use a 6" drop to the wye right at the machine for this application, even with the hi-vac Oneida. You need tremendous air volume flowing for a sander like that; velocity isn't the larger concern, IMHO.
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The most expensive tool is the one you buy "cheaply" and often...
[OP]
Contributor
Glad I dropped in to ask the question. I'll go ahead and branch off of the 8" with an 8"x6" lateral wye and 6" drop to the machine. I plan to use a 6" blastgate before a 4"x4"x6" true wye, then flexible 4" hoses to the machine. Here's a pic showing where I plan to place the sander. The 8" main is in the background.
shop 001.jpg
Last edited by Steve Mathews; 08-08-2022 at 5:47 PM.
Moderator
That will work, Stever. Keep the flex as short as possible for best performance.
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The most expensive tool is the one you buy "cheaply" and often...
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