So as not to further hijack the recent thread on ducting I thought it best to start my own, but if mod's deem appropriate feel free to combine.
I plan to base my extraction on a twin motor camvac extractor, with a 4" outlet (but who knows you may convince me otherwise). There is a very handy sized space under the extension of my tablesaw where it can live. You may recall I have a shelf around two sides of my workshop as the block walls were thicker than the timber frame that sits on them, this is rather conveniently a little over 100mm wide. Therefore, I am thinking that I can route the ducting around the workshop sitting on this shelf for much of its journey, though another 'leg' may go across the ceiling to reach bandsaw, but I am still thinking about this.
My main question is this. The outlet on the Camvac is 100mm, but if I really wanted I would have space to run 125mm (or maybe even 150mm) ducting to within a short distance of my machines. Presumably to do so I would put a, say, 100mm to 125mm adaptor on the Camvac and then an adaptor taking it down to the size of the outlet from the machin in question. As the whole system starts with the Camvac's 100mm outlet, is there any benefit to doing this? My gut reaction is 'no', but having read up a little on the subject I am thinking there may be benefit as suction loss seems to be in large part down to the friction created as the air passes through the ducting and if I am reading it correctly this is reduced the larger the diameter of the ducting becomes.
I am also thinking of using ventilation ducting, rather than ducting marketed as being for woodwork dust extraction as the cost difference is eye watering. I have now found a source of 2m lengths at £5.76 versus Axminster charging about £16 for a 900mm length, even taking delivery into account the saving is worth having. The technical description does say it is for lower pressure extraction, but having exchanged emails with the company selling it the reason seems to be the manufacturer specifies larger diameter ducting for higher extraction, it has nothing to do with the wall thickness of the ducting pipe.
As ever, words of wisdom much appreciated.
Terry.