on the rotor for rotating the rotor as the drilling fluid flows therepast application_number US 45800509 A description referring to fig1 a drill string 10 is illustrated down a bore hole 8 in a soil or rock formation 6 the drill string includes a drill bit 12 at a lower end 14 thereof and an apparatus according to a first embodiment shown generally at 20 for vibrating the drill string within the bore hole 8 the apparatus 20 may be located proximate to the lower end 14 of the drill string 10 or at an intermediate portion 16 of the drill string 10 it will also be appreciated that a plurality of apparatuses 20 may be located at a plurality of locations along the drill string turning now to fig2 the apparatus 20 comprises a tubular body 30 a flow separator 60 and a rotor 80 the tubular body 30 has a cylindrical wall 31 having inner and outer surfaces 32 and 34 respectively extending between inlet and outlet ends 36 and 38 respectively the inner surface 32 defines a central bore 40 the tubular body 30 includes at least one radial tubular body port 42 extending therethrough the tubular body port 42 may be formed as a bore through the wall 31 or may optionally be located within a tubular body port insert 44 as illustrated in fig2 the use of a tubular body port insert 44 facilitates the interchangability of tubular body port 42 of differing sizes as will be further described below as illustrated the tubular body port insert 44 may be threadably secured within the wall 31 or by any other suitable means such as by way of non limiting example compression fit latches.