Turbodrill with a reduced drilling fluid pressure on a floating piston

Claim 1

A turbodrill having rotary shaft means supported within a tubular housing and having a lower end extending therefrom for carrying a drill bit, a turbine within the housing for imparting rotation to the drill bit via the shaft means by being actuated by the flow of drilling fluid therethrough, a bearing rotatably supporting the shaft means adjacent said lower end thereof, seal means positioned below said bearing between said shaft means and said housing, and a floating piston positioned between the shaft means and the housing and defining an upper end of a lubricant chamber for containing a lubricant for lubricating the bearing, the floating piston also defining a lower end of a drilling fluid chamber above and opposed to the lubricant chamber for receiving part of the drilling fluid from the turbine, second seal means positioned between the shaft means and the housing above said drilling fluid chamber for restricting the inflow of the drilling fluid from the turbine to the drilling fluid chamber; and means defining a passageway through the housing for communicating the drilling fluid chamber with the outside of the housing; whereby the pressure of the drilling fluid in the drilling fluid chamber acting on the floating piston is made approximately equal to the pressure of the drilling fluid outside the housing.