an o ring 116 or other suitable means the central bore 40 also includes a rotor portion 120 sized to rotatably receive the rotor 80 therein the rotor portion 120 ends in a second shoulder 122 for retaining the rotor 80 within the rotor section 120 the flow separator 60 serves to retain the rotor 80 against the second shoulder the apparatus may also include a wear ring 124 sized to abut against the second shoulder 122 and provide an enlarged surface to retain the rotor 80 within the rotor section 120 the wear ring 124 may be sealed within the rotor section by an o ring 126 or the like as shown in fig2 the wear ring 124 functions as a thrust bearing against the rotor 80 the wear ring 124 is easily replaceable and expendable grooves in the bearing surface help prevent debris from collecting on the bearing surface thus improving the wear rate multiple material types can be used depending on the application alternative bearing types such as rolling element bearings are also applicable the rotor 80 and the flow separator 60 may be inserted into the tubular body 30 through the inlet end 36 of the apparatus and are sized to fit through the internal threading 46 as described above the flow separator 60 is a flow distributing device which directs a prescribed amount of drilling fluid flow through to the vanes 98 of the rotor 80 as illustrated in fig2 drilling fluid is pumped downwards within the drill string 10 and therefore through the apparatus 20 as indicated generally at 142 by correctly sizing or adjusting the rotor passage 64 the flow separator will direct sufficient flow through the rotor 80 to allow the rotor to spin.