surface 34 the use of a throttling cross section will assist in controlling the volume of drilling fluid vented therethrough the tubular body port insert 44 can be sealed to the tubular body 30 with an o ring to prevent washout and backed with a snap ring to prevent the tubular body port insert 44 from backing out the inlet and outlet ends 36 and 38 of the tubular body 30 can include interior and exterior threading 46 and 48 respectively for securing the tubular body in line with the drill string 10 it will be appreciated that the interior and exterior threading 46 and 48 will be of a conventional type such as a pin box type to facilitate ready connection with the drill string 10 the tubular body 30 can be of steel construction or of any other suitable material and can be surface hardened for durability and abrasion resistance the flow separator 60 comprises a disk shaped body having a central bypass passage 62 and a plurality of rotor passages 64 distributed radially around the bypass passage the flow separator 60 is sized to be located within the central bore 40 of the tubular body as illustrated.