Just finished duct work on the DC

[Dennis in Mtl]

Still have to build the blast gates...

http://www3.sympatico.ca/mcfern/DC-001.jpg
http://www3.sympatico.ca/mcfern/DC-002.jpg
http://www3.sympatico.ca/mcfern/DC-003.jpg

[Bob, in Lachute, Qc.]

Hi Dennis, great stuff. Man, you don't waste much time. Glad to see you got the spiral pipe. Did you get a good price???

Dennis, I hate to tell you this, but there are a few serious problems, at the drops. Two that I see right off the bat, are that "T", and the table-saw reduction. What size port are you using for the tablesaw??? 4"?, 5"?

We can sort that out pretty quick, and optimize that flow. Instead of a reducer there, off the 6" drop, you should have a wye. Either a 6"x5"x3", or a 6"x4"x4".

I recommend you use a 5" connector, at the saw's base, if you can. That way, using the 6x5x3, you can run 5" porting to the saw base, and 3" to an overarm cover. If you don't have one yet, no problem. Just leave that 3" port open, or run it to a small machine, like a drill press. The 6" drop, needs the combined flow of those two ports, to produce adequate velocity, in the 6" drop, and main, without adding resistance.

If you're gonna use the 4" port that came with the saw, then use a 6x4x4 wye, and again, run that second 4", to another machine, until you get an overarm blade cover. You could also just leave it unconnected, but operational. Don't close it.

As far as the "T" fitting goes, on the first drop, well, you need a 6"x6"x6" wye there. The "take-off" for the drop, should be a 45 degree take-off. You can add a second 45 degree elbow to that. This will give you a nice long-radius turn, with little resistance.

Take a look at "Gus, in Maple's" elbows and wyes. He did a pretty good job there.

http://www.workshopbuzz.com/forum/viewtopic.php?t=202

Good luck Dennis, I'm off to a party (guitar jam)shortly, but I'll get back to you soon if you need some help.

All the best, Bob

[Bob, in Lachute, Qc.]

Dennis, I can't see any blast-gates there. You'll need one for the floorsweep, and one, just after the "T" for the floor sweep, or at least before the first drop after the floorsweep.

The drops, are an "either/or" thing. You use one drop, or another.

As for the floorsweep, be very careful. 1100cfm through a floorsweep, can get you in trouble pretty quick. You might suck up more than you bargained for. Just ask Garrett. You'd probably be better off to put another 6x4x4 wye there, too. Use one 4" for the floor-sweep, and that gives you a second four inch "tap" to something else.

Good luck, Bob

[Bryan in Woodstock]

I don't like floor sweeps, just stir up more dust with a broom. I think a shop vac is better. Had a floor sweep in a shop once though. Cutoffs, etc. sure made a racket hitting the steel fan blade!

[Dennis in Mtl]

Hi Bob,

How was the jam session ? Sounds cool.

I purchased 30ft of 6in spiral for $50. They had quoted me $335 for the whole setup. That was a bit too rich for my blood. So I decided to just get the straight pipe from Mega and got the rest from a local Rona hardware store.

My TS has a 4in dust port. I used 2 reducers to get to 4in from 6in.

As far as the "T"s are concerned, I didn't realize that that might be an issue. You recommend using wyes instead. Although I think I understand why the wyes might be more efficient with the air flow not having to go thru a 90 degree bend, will the wye really make a noticable difference?

You mention installing a wye (6-4-4) at the TS drop and keep the second 4in port open. Won't that cause me to lose a lot of vacuum at the TS?

I didn't put any blast gates yet. Mega was quoting $26 each. Until I either build them or find something cheaper, I am using end caps.

[Wally in Calgary]

Denis-- Here's a simple blast gate that uses just 1 coupling and a little bit of scraps. It works great.
Cheers Wally!!



http://www3.telus.net/public/cass1976/Wally'sWoodPics/Blast%20Gate%203.JPG

[Bob, in Lachute, Qc.]

Nice job on those Wally. Does the trap, go right through, Guillotine style?? The guillotine style, helps prevent jams. Nicely done.

All the best, Bob

[Bob, in Lachute, Qc.]

Hiya Dennis,

We had a ball tonight. Good friends, good music, and the sweeeeetest corn-on-the-cob, this side of heaven.

Dennis, I have no email currently, 'cause I got hit with a virus today. I'm partially up and running, but I'll get to the email, tomorrow, errr, today. Gonna be a late breakfast. It's after 4:30AM now.

Dennis, the "T"'s definitely are not good. Not major, but not good. You're fairly deep, into a very good dc, very good ductwork. Trust me, you'll be very happy changing to those wyes like Gus has. They're only 7-8 bucks a piece, too.

The reducers, are DEFINITELY, a "No-No". Here's why. The dc, will try to pull all 1100 cfm, through that 4" port. In order for that to happen, you'd need a velocity of over 12,000 fpm. That would DRAMATICALLY increase static pressure resistance. This will reduce the total flow by about half.

Things will "look" good, at that 4" port, it will appear STRONG, But, the 6" drop, and the main, will now be flowing less air, so velocity there would be reduced, possibly to 700 fpm, below the minimum 3500 fpm level required You'd be at roughly 2750 fpm

Opening that second 4", will also feed 550 cfm to the drop duct, and main, so you'll be back to full velocity, and well beyond what you need at over 5000 fpm. Major difference.

Drops, should always flow, equal to the connectors, or vice-versa. If you have a 6" drop, then that 6x5x3, or 6x4x4, or a single 6, is best. The drop will be optimized.

While I'm thinking about it, any floor-sweep, should always have a safety grille, at the opening, to prevent sucking up something you don't WANT sucked up. At that velocity, you could seriously damage your impeller, with a screwdriver, or a stray pet, lol. You may want to consider adding a pre-separator, too. Cheap to build, and effective and convenient. You've got plenty of power for it, too.

The end caps, should be ok for now, but the blast gates will be sooo much more convenient.Try to have the gates go completely through the opening, guillotine style.

Well, see ya later, I'm off to lala-land. goodnight. Bob

[Rick in Brantford]

Dennis,

My background is hydraulics, but air flow in a conductor shares many of the same characteristics.

The volume of flow in your duct piping has a direct relationship to the area of the conductor. I think you know that.

The part that isn't so easy to see is when you double the size of a conductor you roughly quadruple the flow, so when you increase the conductor size 50% you roughly double the flow. This works the exactly the same when you reduce the conductor. This is all based on area dimensions.

Area is calculated using the formula 3.14(pie) multiplied by radius squared or 3.14XRXR. The area of the 6" pipe is 28.266 square inches. The area of the 4" pipe is 12.56.

With 2 - 4" drops off of the 6" and 1 - 4" blast gate closed, the impeller is trying to move all the air through a single 4" opening and it can't acheive that. There may be some increase in air volume through that opening, but not double, and it will not be enough to satisfy the impeller demand. The result is increased negative pressure in the conductor. Velocity (speed) of this reduced air movement will increase signifigantly in an attempt to satisfy blower demand. There is also an increase in static pressure at the single 4" gate. That's why you will feel more suction there than you will at the end of the 6" opening.

Basically the blower is starved of air, hence the suction (vaccuum/negative pressure/increased static pressure). Opening the second 4" gate satisfies the blower demand and allows for correct air velocity and static pressure at each of the gates BUT you still have half the air flow at each of the 4" gates compared to a single 6" pipe due to the area.

The term "static pressure" is a measurement of the difference between atmospheric pressure and the negative pressure in the conductor.

You must open the correct number of gates so that the area of the open gates equals the area of the main trunk which in turn is hopefully sized correctly for the impeller flow.

In all the reading I've done i have not seen any explanation of how conductor (or piping) area affects air flow. I hope all I've said is correct, maybe Bob can critique for me (please), and I hope this makes sense for some of those who weren't quite understanding it.

Rick

[Doug in Burlington]

Denis
I built similar ones but used 6" 'fish collars' instead of the plastic collars, available at HD for $1-$2. Cut a 6" diameter hole in a 1/8" piece of hardboard, bent the tabs on the collar and then sandwiched it to a 1/2" piece of plywood. Put two of these assmeblies together with a couple of 3/16" spacers and a 1/8" hardboard gate and you are done. Total cost under $4! They work well. Key is to make the spacer slightly larger than the gate. That way, when the DC pulls on the closed gate it has room to move and get sucked against the fixed part, improving the Vacuum seal. (make sure the smooth side of the hardboard faces the suction side of the collection system.
Regards
Doug

[Dave in Acton]

This is a pic of my new preseparator. The following pics show the new 6" spiral piping routed through out the shop.


http://www.canadianwoodworking.com/chat/pics/pic128756.jpg

[Dave in Acton]

This is the 6" t0 4" Y-pipe to the router table and the mitre saw.


http://www.canadianwoodworking.com/chat/pics/pic128757.jpg

[Dave in Acton]

This is the 6" spiral piping to joiner.


http://www.canadianwoodworking.com/chat/pics/pic128758.jpg

[Dave in Acton]

This is the 6" spiral piping to the table saw. Thanks for looking.

Dave.


http://www.canadianwoodworking.com/chat/pics/pic128759.jpg

[Ed/Leaside]

For simplicities sake, I factor out the value of pi when working with the relative cross sectional areas of ducting as follows:
2" (1)
3" (2.25)
4" (4)
5" (6.25)
6" (9)
7" (12.25)
8" (16)
Now it is easy to see that if I have 3 open 4" ducts coming off the lathe, I'll need a 7" duct to the blower.

[Bob, in Lachute, Qc.]

Hi Rick,

Nothing to "critique" there. That's an excellant explanation of the ducting.

In a dc, the fan-wheel's mechanical efficiency, size, rotation speed, and relative resistance incorporated into the blower's design, will determine it's flow characteristics, and how it deals with added static resistance.

Some fan-wheels, are better equiped to deal with added static pressure increases than others. This is especially true of "caged" back-inclined fan-wheels. With this type of wheel, none of the air will be able to "slip" off the side of the fan-wheel's blades during rotation, because the "Cage" prevents that from happening. All of the air that is moved by the blades, get's projected to the fan-wheel's blade tips, which is the highest speed point, of the wheel. This is the type of fan-wheel that Torit-Donaldson uses in most of their cyclones, as well as many other industrial cyclones. These are "clean side" fan-wheels, capable of dealing with "SOME" small material hits. Mechanical efficiency, is roughly 85%, and they require less horsepower to drive. In other words, more of the energy used to drive the fan-wheel, gets converted into air movement(work).

With a radial fan-wheel(uncaged), these are better suited to material handling. "Stringy" material, will flow without fear of "hang-up". The trade-off, is that they're not as mechanically efficient(generally, 65%). Some of the air will slip off the side of the fan-wheel's blades during rotation. Not all the air, gets projected to the tips.

Many high pressure blowers, use radial fan-wheels, however. The blower housings are very narrow, as are the fan-wheel blades. Blade diameter, rather than width, is important there. The close proximity of the blower housing, to the side of the fan-wheel's blades, makes the housing act much like a "cage", and more air get's projected to the blade tips. Because of the large diameter, the increase in airspeed, from the fan-wheel's hub(slowest speed), to it's tips(fastest speed) creates more static pressure capability. You'll commonly see high pressure blowers rated to 50" SP, which is MUCH higher, than you'll ever see in a dc.

The Belfab JJ, incorporates some of these elements in it's blower design. The blower housing, is quite unique, and patented. While it uses a radial material handling wheel, the blower housing is very close the the fan-wheel's tips, enough to flow material, but, close enough to benefit from a claimed 30% increase in static pressure performance. This partially accounts for that unit's strong suction. It's engineered and optimised for woodworking applications. Another feature, is the elimination of the blower housing "outlet", in the traditional sense. There is no "spiral" to deal with, and none of the assosciated resistance. The entire rim of the fan-wheel, IS the outlet, therefore, air exits the fanwheel, at it's strongest speed point, and no spiral resistance.

Regarding ducting, dc's won't compress air on the negative side(intake). They work essentially at atmospheric pressure. They're "air movers". Some slight compression can occur at the postive pressure side (outlet) if velocities exceed 3500fpm. Excessive restriction at the outlet side(outlet restriction/dirty filters/under-sized filters), create "pressure drops", impacting on the intake side.

All the best, Bob

[Bob, in Lachute, Qc.]

Well holy smoke, Dave, long time no see. All I can say is Wow!!!. I'm REAALLLY impressed with that ducting.

Veeeery nice set-up. Beautiful long radius elbows. That wye is wonderful. That spiral flex looks like J.R. Normand's flex, is it???? Very high quality flex.

I like your roller-stand, for the dc, too. I made mine a lil' longer, to deal with balance(motor weight).

How do you like your Belfab so far??? Are you satified with the draw. Any comparison to your other dc??? Do you feel you got good "value"??

Thanks for sharing those pics. Very impressive set-up.

All the best, Bob

[Dave in Acton]

Hi Bob

Nice to hear from you too. I know you thought someone would find me in my shop with my feet sticking out of the J.J.'s intake. Ha!Ha!I wasn't in a rush to get the 6" spiral pipe up. Just wanted to get it up right the first time. The spiral flex pipe looks like J.R. Normand's but it comes from a company called Rubberline. They are just a little cheaper and a lot closer to me. Bottom of the roller stand is full of concrete so it is bottom heavy. I am really satisfied with the draw from the J.J. It cleans all of the sawdust up from each opening. A lot better than the old D.C. The pre-separator works greatafter experimenting with different size elbows. There isn't any sawdust in any of the bags at all. It all goes into the barrel.

Thanks again for your e-mails and info off of this great Wood Forum.

Dave

[Steve In Kemptville]

The construction of your gate looks very familiar, was this a version of the CAD plan I posted many months ago?

Just wondered if anyone had built one from my plan?

[Wally in Calgary]

No Steve -- I built those a couple of yrs. ago. I do remember seeing one of yours when you first built one though. They are real easy to build (and cheap) so I make one up whenever I need it.
Cheers Wally!!

[Dennis in Mtl]

I now have a better understanding and will implement your recommendations. Thanks for taking the time to contribute to this thread.

Dennis

[Bob, in Lachute, Qc.]

Great to hear you didn't have to be pulled out of the DC, lol;-)). Dave, that flex looks so nice and supple. Maybe you could share that company's address with us. I'd be happy to recommend a good product like that, and I might even buy some, myself. Can you give me an idea of price?? Do they sell only minimum lengths?? Any cutting fees???

Up 'til now, the only place I found, that sold short lengths, with no cutting charge, was Normand.

That looks like a pretty large duct network. Interesting that the JJ can handle that and the preseparator too. Lot's of ways to tweek that separator too, if the need arises.

Again Dave, well done. Very nice set-up.

All the best, Bob

[Bob, in Lachute, Qc.]

Good stuff Dennis. I know you'll be well prepared for future additions, as well. You won't regret it.

If I can get my email up and running, I'll be here if you have any questions.

All the best, Bob

[Gus in Maple]

Hi Dave,
Great looking setup, if you don't mind could you email me. I have a few questions I would like to ask you.
Thanks,
Gus

[Steve In Kemptville]

You're look very nice (fit & finish wise).
My versions were down & dirty (get 'em done quick & put 'em in service) jobs and not quite as pretty as yours http://www.canadianwoodworking.com/forum/images/smilies/wink.gif

How did you thickness the spacers so the knife/slide gate was slightly thinner? I used a couple strips of masking tape applied to the same thickness hardboard spacers to give the extra clearance needed, worked very nicely and really quick to do.

Regards,
Steve.

[Wally in Calgary]

I did the same Steve, only I used duct tape and 1/4" melamine two sides. They slide nice and seal great.
Cheers Wally!!

[Dennis in Mtl]

Hi Doug,
I'm not familiar with fish collars. Where, within HD, are these located. What do they look like. Seems like a viable starting point for a gate.

thanx
den

[Doug in Burlington]

Denis
The fish collars are just round metal collars with a crimped edge to fit inside a round duct on one side and tabs to bend over on the other end. I presume the "fish" name is because the tabs kinda look like gills on a fish (if you have a good imagination!). They are used to join a round duct as a takeoff on a rectangular main duct. You cut the round hole in the rectangular duct, slide the collar into the hole and then bend the tabs over to hold it onto the rectangular duct. For a blast gate you just need to use a thin material to bend the tabs over. I used 1/8" hardboard but you could also make them out of Aluminium or steel (just harder to cut the hole!). I only saw 6" collars at the HD I was at, presumably you can get them for other duct diameters. They were in the bins were they have all the Y's, Tees and elbows for HVAC ducting. Hope this explains it.
Regards
Doug

[Dennis in Mtl]

Got it. Thanx