Protected lubricant reservoir with pressure control for sealed bearing earth boring drill bit

A rotary cone rock bit for use in a borehole, comprising:

• a bit body including a plenum therein and a plurality of legs extending therefrom, said plenum having a plenum surface and terminating in at least one nozzle adjacent said legs, said bit body including a threaded connection for attachment to a drill pipe, said drill pipe having an inside diameter for the passage of circulation fluid, an annulus being defined between said body and the borehole;
• said circulation fluid passing through said plenum and said nozzle, said circulation fluid creating a pressure drop across said nozzle such that the pressure of the circulation fluid in said plenum is greater than the pressure of the circulation fluid in the annulus;
• a roller cone rotatably supported on each of said legs;
• a sealed bearing system between each cone and the leg on which it is supported;
• a lubricant reservoir in fluid communication with said bearing system and containing a lubricant, said reservoir having an installation opening in said plenum and being at equal pressure with said annulus.

A rotary cone rock bit, comprising:

• a bit body including a plenum therein and a plurality of legs extending therefrom, said plenum having a plenum surface and terminating in at least one nozzle adjacent said legs, said bit body including a threaded connection for attachment to a drill pipe, said drill pipe having an inside diameter for the passage of circulation fluid;
• said circulation fluid passing through said plenum and said nozzle, said circulation fluid creating a pressure drop across said nozzle such that the pressure of the circulation fluid in said plenum is greater than the pressure of the circulation fluid in the annulus;
• a roller cone rotatably supported on each of said legs;
• a sealed bearing system between each cone and the leg on which it is supported;
• a lubricant reservoir in fluid communication with said bearing system and containing a lubricant, said reservoir having an installation opening located on the bit body exterior, a second opening in communication with the plenum, and a pressure balancing device positioned in said second opening such that pressure in the reservoir is substantially equal to the pressure in the plenum,
• wherein said lubricant in said reservoir is subjected to a pressure of no more than 100 psig as compared to the circulation fluid pressure in said annulus.