Optimizing Duct Sizes

[Dan Butler]

I have a question that I am sure many of you know the answer to. When using a 6" main duct, I understand the recommendations for keeping the combination of sub-runs as close to the total square inches of the 6" area as possible. For example, many recommend a combination of a 5" and 3.5" run for the upper and lower collection points on a table saw that is connected to a 6" run. With the area of the 6" at approx. 28.3 sq. in. , the total of the 5" and 3.5" is approx. 29.2 sq. in. Since it is very difficult to size sub-runs to exactly match the 28.3 sq. in., is it better to choose a combination of sub-run duct sizes that total either slightly higher or slightly lower than the 28.3 sq. inches? Or, does it really matter at all in actual practice? Thanks for any help you can provide.

[David Kumm]

Dan, for a real answer you need to know what velocity or CFM you are getting through the 6" pipe. If the system is delivering at the low end of the recommended range you want to stay under. If way above it won't matter if you go over. It also depends if you are servicing the table saw and what type of collection you have inside the machine. Some saws have a 4 or 5" port but reduce to a smaller flex inside the shroud so you can't use all the cfm anyway. The minimum recommended fpm for vertical lines is 4000 although I try to stay above 5000. 6000 is even better but keep in mind I'm a cult of one in that belief. Dave

[Michael W. Clark]

I second what David said about knowing your available volume. Maybe try a 5" and 3". Only about 6% different from the 6" area. You may need a gate in the 5" if you need more flow up top.
Mike

[Dan Butler]

I have a ClearVue 1800 but I'm not sure what the fpm is and have no way to measure it. I was just wondering if there is a general rule of thumb of whether to go over or under the 6" sq. in. area for any given situation.

[Dick Mahany]

I recently had the same concern while installing my Oneida V3000 with 6" pipe. I decided to run 6" lines everywhere, with 5" to the cabinet on the Unisaw and 4" to my home made upper guard. The total sq. in. is slightly over the 6'" total, however it works great. I could always throttle down either of the branches with the blast gates, but haven't found it neccessary.
IMGP3598.JPG

Other pics can be seen here:

https://picasaweb.google.com/dmshops...ustCollection#

[Dan Butler]

Thanks Dick. I looked at your shop pictures....nice looking shop. I like the way you designed your portable tree.

[David Kumm]

The clearvue will deliver enough cfm that you can divide the 6" and increase the area some. If you know an HVAC guy ask to borrow a fan type anemometer and measure the velocity at the end of the flex as it is about to enter the machine. Will tell you what you are getting. I bought one on Ebay for about $100 and use it for testing the DC and paint booth. Dave

[Michael W. Clark]

You would probably want to use a 5" and 3" or 5" and 4". A 3.5" may be hard to find. As far as over/under on sizing, I would calculate what I need, then go to the nearest duct/hose size that is commonly available.

I'm going to run a 4" to my router table and split it into either two 3" ducts or a 3" and ~2". One for the cabinet and one for the fence. I may go with the two 3" ducts just because fittings may be more available and I know I should have some extra capacity in the 4" line. Mathematically, I would need two 2.83" ducts or a 3" and a 2.65" duct. I'm not 100% sold on the 3" yet for the top because I think the ~2" hose will be more flexible. I say ~2" because I can't remember what hose sizes and fittings are available in the 2" - 2-1/2" range..

Mike

[Ole Anderson]

I went with a 5" on the bottom and a 3" on top of the TS, and it works great although the pipes don't join together immediately, the bottom goes into a 6" then into a 7" while the vertical 3" goes to a 4" blast gate then a 5" before hitting the 7" main.

[Michael W. Clark]

Ole,
That looks like a 1023 Grizzly saw, that's what I have. I don't want to change topics, but if this is the case, can you PM me what you did for the blade guard dust collection? I would like to add that to mine.
Mike

[Jay Radke]

I recently had the same concern while installing my Oneida V3000 with 6" pipe. I decided to run 6" lines everywhere, with 5" to the cabinet on the Unisaw and 4" to my home made upper guard. The total sq. in. is slightly over the 6'" total, however it works great. I could always throttle down either of the branches with the blast gates, but haven't found it neccessary.
IMGP3598.JPG

Other pics can be seen here:

https://picasaweb.google.com/dmshops...ustCollection#

Dick,

Thanks for the pics. Really enjoyed looking at them. They have given me many ideas. I too have a mobile workspace. Because of that I have not taken the plunge into the cyclones yet. Though I had thought about one of the mobile cyclones. But now looking at your setup I can see what I should be looking at in the future.

Thanks,
Jay

[David Giles]

Dan, if you already own a 1.5-2hp dust collector, then it makes no appreciable difference. Any 4" section will limit the total flow. 6" line keeps the pressure drop low, but the small DC impellers can only pull so much air. I ran 6" line everywhere possible and it works okay. Now if you do not have an existing DC, one can design the duct work, then buy a blower/motor to match the system flow/pressure drop characteristics. But most of us start with an underpowered DC, modify the ductwork to minimize pressure drop, then finally buy a 3-5Hp cyclone.

[ian maybury]

We talked it before Dan, but as has been suggested the precise matching of the size of say the top guard and cabinet ducts to say a 6in main duct isn't all that critical if you're running a big blower that's giving something very comfortably over the 4,000FPM minimum in the main duct, and still has significant pressure capability in hand.

As has also been said - you can pitch the total area slightly larger than the main in this case, favouring whichever of the branches you feel may benefit most from some extra puff. You can like wise reduce the total area slightly with less impact on the flow.

e.g. a big system as before if run with quite a long (say 15ft) flexy hose to a floor sweep is still pulling hard enough to have no trouble picking up quite large chunks of wood (say 1in + chunks), and transporting them back along the flexy and on through the much larger 6in header to the cyclone. Against that it doesn't stop working, but it does lose enough of the pep through the 4in hose to be very obvious and for the transportation to become a bit lazy if one or more other 6in drops are open at the same time.

When your fan is marginally sized the situation becomes a bit more sensitive. Add some extra resistance, and a fan that depends on low resistance to make the numbers will be more severely influenced by this. Reduce the resistance a bit, and motor that was already not too far off full load amps could get tipped over the edge. Favour one branch over the other by giving it disproportionately more of whatever extra cross section/duct diameter is possible and it may hog enough flow to severely disadvantage the other more restrictive branch...

ian

[Ole Anderson]

Ole,
That looks like a 1023 Grizzly saw, that's what I have. I don't want to change topics, but if this is the case, can you PM me what you did for the blade guard dust collection? I would like to add that to mine.
Mike

3" SharkGuard. And I used a big piece of magnetic sign sheeting to cover the arc shaped opening in the front of the cabinet when I am not doing a miter cut. Don't know if they improved it over the years, but Grizz could do a better job of underblade dust deflection.

[Clint Olver]

There is a thread on the clearvue forum about this. It doesn't really matter. Some guys go 5" and 3", some go 6" and 3", some 5" and 4", - all report good dust pick up. I read one thread of a guy who changed over from 6 and 3 to 5 and 3 and reported no noticeable difference. I went with 6" and a 4" that tapers to a 3", so really 6" and 3". Works great.

C