Splitting DC lines...

[rjwaldren]

I have a quick question on splitting DC while maintaining maximum airflow.

My thinking is that if I keep the total area of the branches as close the area of the 4" mainline I should get what I'm looking for without starving the DC. For instance a 4" DC hose has a face area of 12.6", so I can have a 3" (7.07sq in) and a 2.5" (4.91sq in) branches and still be moving the roughly the same volume of air.

I realize theory and reality are 2 different things and design has a lot to do with it, but is my basic thinking correct?

The idea is to split an single connection between the bottom and back DC chute on the BT3100 and between the router chamber and fence on an enclosed router table. I'd like to make it as efficient as possible... I'm sick of the mess.

[Uncle Cracker]

The DC will draw the most air through whichever path has the least resistance. The cross-sectional area of the ducting is only part of the equation. The air access to the router cabinet and to the fence, along with the length of the piping in each branch, are the rest of it. You might be able to control it to some degree by making the intake area independently adjustable between the two branches. A temporary hookup might give a clue as to the expected results.

[rjwaldren]

I see what you mean. It shouldn't be a big problem on the BT since both lines will essentially be pulling from the same cavity. Also the blade does a good job of setting the majority of the dust into motion directly into the 2.5" hose.

On the router table I was thinking of an adjustable slide vent on the router chamber door to accommodate the variance in airflow due to different size rings at the bit opening.

I hadn't thought about dampers at the source.

[Uncle Cracker]

I hadn't thought about dampers at the source.

I think the effect would be the same, whether they were at the source or at the other end. The idea is just to balance the two dynamics.

[LCHIEN]

part of the reisstance is the are thru which you suck it, the other part is the surface area.

For exampe If you have 2 4-inch hoses or 1 six inch hose, the 4-inch hose pair will have less cross-sectional area actually (~24 square inches) than the 6-inch (~27 Sq in), in addition the two-four inch hoses will have ~288 sq inches of internal surface area per run-foot vs ~216 sq inchs or are per run-foot, more for the air to drag over.

So 2 4" hoses is worse than one 6". On splitting, the airflow will tend to even out, more air will go the path of least resistance but the increased airflow will increase the resistance so it will tend to equalize. If you have two unequal sized lines, then more air will tend to go in the larger hose and this will be the equilibrium.

[billfrommich]

Also bear in mind that if you are collecting waste (chips/dust) from two different areas on a machine you don't necessarily want or need the branch flows (and there are several factors, such as flow velocity and flow volume)to be identical, as the type and amount of waste being produced may be different. For example, one branch line might need to handle large chips that are confined and fall naturally (by gravity) towards the bottom of a machine's cabinet while the other branch might have to get the fine dust "spray" being generated at the machine's cutting edge. Some trial and error is probably unavoidable.