Dust collection ducting - more straight runs or less curved runs? blast gate to close

[jeff norris 2011]

I am shifting my duct work around and I am left with on awkward run to the cabinet saw lower collection.

hopefully this picture gives you an idea of layout:

IMG_2909.jpg

My choices are:

1. include a direct but independent run that increase the total amount of duct work by about 7' (run c)
2. connect a drop that I have right of my TS and looping it back to the cabinet (run b)

option 1 is what I have right now and I get about 500 cfm to a shop made 5" port. I don't use this port that much as my blade guard dust collection is more effective. so this port is used more for clean out or when I can't use the guard for a cut.

option 2 takes advantage of the run that goes to my jointer, bandsaw, planner and router table. (I use to drop downs and connect what ever I am using. It is obviously a super inefficient path to the table saw, but as the blast gate is before the drop down it reduces the overall ducting in the system

So to the question - does unused ducting have a major effect on performance?
If so is it worth having blast gates to block off entire branches when not in use?



FYI - I run 5" duct work with a mix of 5" and 4" ports. My DC is a true enough 2hp 11" impeller POS model made off shore that does not exist anymore. Despite its dubious origins, the performance has been good enough for my needs as I am not trying to get every micron of dust and I am happy wearing my respirator and/or working with the double garage door open or even outside.

[Andrew Seemann]

You could work out all the engineering, but it probably doesn't matter significantly either way. If you can do c easily to that as it is shorter, but b probably would work just fine also. I'd probably just pick the easiest one to do and see how it works.

If you only open one blast gate at at time, that is the only run that matters, none of the other ducting has any appreciable effect on the system. It is the length of the active run that matters for performance, not the total length of the system (unless you have a lot of leaks). If you have blast gates at the ends of the runs (i.e. at the machines) you don't need to have them at the wyes in the system. One could maybe argue that they might reduce turbulence, but one could also argue that they could increase turbulence as well depending on where they are.

[jeff norris 2011]

You could work out all the engineering, but it probably doesn't matter significantly either way. If you can do c easily to that as it is shorter, but b probably would work just fine also. I'd probably just pick the easiest one to do and see how it works.

If you only open one blast gate at at time, that is the only run that matters, none of the other ducting has any appreciable effect on the system. It is the length of the active run that matters for performance, not the total length of the system (unless you have a lot of leaks). If you have blast gates at the ends of the runs (i.e. at the machines) you don't need to have them at the wyes in the system. One could maybe argue that they might reduce turbulence, but one could also argue that they could increase turbulence as well depending on where they are.

Thanks, that is what I wanted to hear.