A Dust Collection Question

[sweensdv2]

My dust collector has two 4" inlet lines.  One line I have dedicated to use for my table saw and the other line I move around from machine to machine.  Each of the inlet line have a blast gate located at the dust collector.  If I'm using the table saw I normally close the other blast gate and vice versa so only one blast gate is open at a time.  I've always thought that this is what I should do.

I've never really paid too much attention to the vortex action in the bottom bag of the dust collector but the other day I forgot and left both blast gates open.  I noticed that the vortex action in the bag was much stronger with both gates left open then what I was getting with one open and one closed.  My unscientific mind tells me that I'm getting better air flow with both gates open than I'm getting with only one open.  If that's whats happening then why do I always seem to read that you should close the blast gate to any line not in use?

[TDKPE]

The DC will flow more air with more blast gates open, but the air flow through a given hose will be reduced as you open more gates.  

A single 4" hose to a TS is not really flowing all that much air, so I wouldn't want to make it worse by opening others, unless of course, the other is to an overhead blade guard.

[MstrCarpenter]

Just don't run it too long with all the blast gates closed, you'll let out that magic smoke.

[fredhargis]

Just don't run it too long with all the blast gates closed, you'll let out that magic smoke.

Nope, that's not the way things work. though it is a common misconception. It's the opposite....with both gates open the DC is moving more air, and the load on the motor increases. As it tries to come up to stated speed it draws more amps...in extreme conditions that lets the smoke out. (You can easily test this your self with an amp meter). Anyway, what Tom said is spot on. Leaving both gates open reduces the flow at each hose, I wouldn't do it unless this is a really big DC.