Downhole drag reduction apparatus

A downhole drag reducing apparatus 18 comprises a mandrel 20 and a bearing sleeve 24 mounted on the mandrel 20, such that the mandrel 20 and bearing sleeve 24 are rotatable relative to each other. The bearing sleeve 24 defines a bore wall engaging surface. The apparatus 18 comprises a reciprocating piston 23 mounted within a piston housing 25 to define a piston chamber 27. The apparatus 18 further comprises a rotary valve assembly 29 operated by relative rotation between the mandrel 20 and the bearing sleeve 24 to cyclically pressurise and depressurise the piston chamber 27 to provide reciprocating movement of the reciprocating piston 23 and the generation of vibration within the apparatus 18.