Hi All, I am designing a vertical venturi tube to be inserted into a 18" piece of ductwork in order to pull steam generated in a 12'' perpendicular duct. I would like to reduce the diameter from 18'' to 6'' at which point i will tie in the 12'' perpendicular duct (nozzled down in size) in which steam will be pulled from the hut. After a short distance the 6'' diameter will be expanding back out to the original 18" (done at a angle of 15 degrees or less). The fan currently attached at the bottom of the 18'' vertical duct work pushes about 4800 CFM with a 10hp 3 phase induction motor. My concern is that I will need a bigger motor to overcome the increase in static pressure and was wondering if anyone had any advise on calculating how much larger (if necessary) my motor would need to be? Also any other design advise on a venturi would be extremely helpful. Thanks.