Plenum in DC system?

[dlminehart]

My HF dust collector, about to be located in a shed outside my garage, will have ducting coming through the middle of the garage wall. The ducting then needs to go 4 different directions: left and right along the wall, up to and then across the ceiling, and also straight down the wall. If I use the standard branching wyes, it will take at least 5 wyes to do the job, plus a ton of 45 degree elbows, and take up a lot of wall that could be better used.

I'm considering having a "plenum" into which the duct from the DC will come. From there, ducting would go out in all 4 directions. If I make the plenum about a foot cubed, there'd be space for blast gates on each of the four ducts. I could perhaps put a polycarbonate sheet on the front, to observe whether stuff was building up in the plenum.

I'd assume this would not be as efficient as a straight pipe, or even as one with a long 90 degree arc. But how inefficient? Anyone have any ideas or, better yet, experience with this?

[BobSch]

I'd consider making the plenum as round as possible, not a square box. Square corners tend to be dead air zones and collect the stuff you're trying to get rid of.

[lkazista]

OK - I'll bite, what is a 'Plenum"?

[LarryG]

PLENUM can mean different things, depending on the application ... in this case, it's like a common chamber to which a number of duct/hose runs will be connected.

I've seen something similar to your idea, David ... I thought on the Internet, and I had it bookmarked, but I can't find it so maybe it was in a book or magazine. Anyway: rather than a cube it was a long rectangular box -- say 6" x 6" x 2' or so long -- with multiple inlets in the bottom, each with a blast gate, and a single outlet to the DC at one end. The top (or maybe it was the front) was Plexiglas so blockages could be spotted easily. It apparently worked fine (what I saw was a photograph of the built unit, not just a sketch of someone's wild-eyed design). So, same concept, just a different configuration.

[crokett]

Maybe I don't understand your setup, but I count 3 T connectors to do what you want to do. First 1 tees up and down, 2nd tees right and 3rd tees left. Connect them with straight pipe and install your blast gates.

[Tom Miller]

Five wyes isn't so many. I would be surprised if I have as few as 5 wyes in my DC system, and I'm in a pretty small shop!

I think you may be better off with lots of wyes & 45s than with a plenum. In your case, this wouldn't really be operating as a plenum, since only one branch will be flowing at a time (I assume). And this is why you'll have trouble. I think you'll have a lot of turbulence, and a lot of dust/chips falling out of the air stream since most of the plenum volume will be dead space.

Is the issue cost of so many wyes or the space they take up? If the latter, I don't see how a plenum helps so much. Are you working with S&D pipe? Do you have any photos of the shop? I would think we could come up with a solution that doesn't take up too much wall.

Regards,
Tom

[dlminehart]

David, I'm trying to use wyes instead of tees, to maximize flow. The S&D wyes have one straight through with a 45 degree branch. They look kinda like this:

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Using these, each wye provides one branch and one connection to the next wye or, in case of the last one, just the last piece of tubing. Still, you're right, branching 4 ways requires only 3 wyes . . . plus 45 degree angles needed to complete the turns.

[meika123]

quote:Originally posted by LarryG

I've seen something similar to your idea, David ... I thought on the Internet, and I had it bookmarked, but I can't find it so maybe it was in a book or magazine. Anyway: rather than a cube it was a long rectangular box -- say 6" x 6" x 2' or so long -- with multiple inlets in the bottom, each with a blast gate, and a single outlet to the DC at one end. The top (or maybe it was the front) was Plexiglas so blockages could be spotted easily. It apparently worked fine (what I saw was a photograph of the built unit, not just a sketch of someone's wild-eyed design). So, same concept, just a different configuration.

I know what you're talking about. Matter-of-fact, I have the article at home. It is in a Woodsmith magazine. All in all, it looks like a pretty good system. This one shows the construction methods, cut sheets, bill of material, etc.
Let me know-if interested, and I could possibly PDF the article to you.

Dave in NC

[LCHIEN]

Some recent BT3 discussions of plenums in DCs and the definition of a plenum following:

http://www.bt3central.com/forum/topi...hTerms=,plenum

http://www.bt3central.com/forum/topi...hTerms=,plenum

http://www.bt3central.com/forum/topi...hTerms=,plenum

Its a Plenum P-L-E-N-U-M.

The dictionary definition is:

A condition, space, or enclosure in which air or other gas is at a pressure greater than that of the outside atmosphere.

However that usually applies to HVAC ducting where it's a space like a box at the end of a duct run. Th box is pressured higher than the adjoining room by the air flow from the duct. A number of vents in the plenum allow air to be blown evenly into the room ( as opposed to a single vent at the end of the duct.

In commercial buildings there is often a false suspended ceiling below the floor above. This space (a plenum) is either pressured or the return air is sucked by the circulating fan. Special ceiling tiles are used wherever a vent (or return air flow) is needed I this way its easy to add or cut off air flow to areas served by the plenum.

Another example of a plenum is in commercial installation s of computer rooms with false floors. The underfloor is pressurized by Air conditioning and the cold air flows up through the computer racks of equipment which are positioned over holes or opening in the floor.

In a vacuum system (for example a DC) the equivalent box is pressured lower and the air is sucked into the box rather than blown out.

A BAFFLE is a wall placed to direct or deflect the flow.

A VENTURI is a narrowing or restriction in the flow path that causes the air velocity to be increased by this restriction.