Patent ID: 7926592

Claim:
A steerable drilling system comprising: a bias unit, the bias unit having at least one actuator operable by pressurized drilling fluid or mud delivered downhole to the at least one actuator, and a separator arranged to remove particulate matter from the supply of pressurized drilling fluid or mud to the at least one actuator, the separator comprising a hydrocyclone located upstream of the at least one actuator to remove the particulate matter before the drilling fluid or mud acts on the at least one actuator, wherein the hydrocyclone includes a housing defining a substantially conical recess having a large diameter end and a small diameter end, an inlet in fluid communication with the large diameter end for providing the drilling mud thereto, a first outlet in fluid communication with the small diameter end for outlet of relatively dirty mud, and a second outlet in fluid communication with the large diameter end for outlet of a supply of relatively clean mud for the plurality of actuators, wherein the separator is arranged such that particulate matter separated from the supply of drilling fluid or mud to the at least one actuator rejoins a flow of drilling fluid or mud towards a drill bit.