Patent ID: 7213660

Claim:
A seal assembly for controlling leakage of drilling fluid between a first stationary portion adapted to be connected in substantially fluid-tight relation to a source of drilling fluid and a second portion adapted to be connected in substantially fluid-tight relation to a rotary portion including a washpipe and a drill string, said first seal portion including a first housing and stack of radially inwardly extending, spaced apart annular stators and a second seal portion including a second housing and stack of spaced apart radially outwardly extending annular rotors, said stators and said rotors being interleaved with one another and being axially spaced apart from one another by a working clearance, said stators and said rotors combining to define an elongated radially and axially extending tortuous path from an inlet region at one axial end of said stack of stators and rotors for receiving drilling fluid confined at high pressure and directing said fluid along said tortuous path to an outlet region at the other axial end of said stack of stators and rotors, said seal assembly permitting said washpipe and said first and second housings to rotate relative to each other in substantially fluid-tight relation except for said drilling fluid passing along said tortuous path between said stacks of rotors and stators, and allowing said drilling fluid to enter said outlet region at greatly reduced pressure.