Quote Originally Posted by Web Goblin View Post
Jonathan,
I think what he means is starting at the extraction unit he would have say a 300mm dia duct which would then plit and reduce down to three or four 150mm or 100mm dia ducts going to three or four seperate machines rather than a single duct reducing down in size.

Ian
Yes, that's what you shouldn't ideally do. If you think of each length of duct in that system as a resistor, with the smaller diameter ones having a lower resistance, then it's obvious why...you're adding a high resistance in series instead of a low one, which is just inefficient. If you have several ducts open at a time then it doesn't really apply, but then you're not going to do that in a home workshop...