US Patent 7213660 Washpipe seal

A controlled leakage seal assembly having 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. The seal includes a first housing and a stack of radially inwardly extending, spaced apart annular stators, and a second seal housing and stack of spaced apart radially outwardly extending annular rotors interleaved with one another. The seal assembly, a cartridge, permits the first and second housings to rotate relative to each other in substantially fluid-tight relation except for the drilling fluid entering an outlet region at greatly reduced pressure. In a preferred embodiment, the seal is held by a sleeve that permits the cartridge to be removed and replaced while the fluid connections to the sleeve remains.