I generally agree with Dave (dbhost) about closing unused gates, however this will depend on the size of the port on the tool. My cabinet saw, CMS, and OS/B sander all have 2-1/4" ports, and when using any of those I have to open a second, same-sized gate in order to let the DC breathe adequately. (The cabinet saw actually has a 4" port, but the internal hose that connects it to the blade shroud is only 2-1/4", and that controls how much air can flow.
Cool, I made my point and someone got it... Seriously though. My point was more along the lines of making sure you don't say try running a 4" system, and leave several 4" gates open at the same time, it kind of kills everything, at least on my 2.5" system it did. (NOW I know why there was a 2" deep pile of sawdust on the bandsaw!)
Comment