Dual function pressure compensator for a lubricant reservoir of a sealed rock bit

An earth boring bit comprising:

• a bit body;
• at least one bearing shaft mounted to the bit body;
• a rotary cutter mounted for rotation on the bearing shaft, defining an intermediate space located there-between;
• a seal disposed between the bearing shaft and the rotary cutter for sealing the intermediate space from an exterior of the bit;
• a flow passage extending from an interior cavity of the bit body to the intermediate space located between the bearing shaft and the rotary cutter;
• a dual function compensator extending between said flow passage and the interior cavity of the bit body, said dual function compensator including an elongate body having a first end in fluid communication with the interior cavity and a second end in fluid communication with said flow passage;
• said dual function compensator having a moveable seal member disposed in said elongate body of said compensator for at least initially being disposed in a first position, adjacent to said first end of said elongate body and preventing fluid flow through said elongate body, and moveable to a second position for passing fluid flow through said elongate body;
• said dual function compensator further including a retainer member for selectably securing said moveable seal member in said first position, wherein said retainer member is selectable for releasing said moveable seal member from being secured in said first position such that said movable seal member is moveable in response to differences in fluid pressure between said interior cavity of said bit body and said flow passage;
• and
• wherein after fluid is expelled from said compensator, said moveable seal member is disposed in said second position within said elongate body of said compensator, with said moveable seal member located aside of a flow path for passing fluid flow from said interior cavity of the bit body to said flow passage.

An earth boring bit comprising:

• a bit body;
• at least one bearing shaft mounted to the bit body;
• a rotary cutter mounted for rotation on the bearing shaft, defining an intermediate space located there-between;
• a seal disposed between the bearing shaft and the rotary cutter for sealing the intermediate space from an exterior of the bit;
• a flow passage extending from an interior cavity of the bit body to the intermediate space located between the bearing shaft and the rotary cutter;
• a dual function compensator extending between said flow passage and the interior cavity of the bit body, said dual function compensator including a tubular body having a first end in fluid communication with the interior cavity and a second end in fluid communication with said flow passage;
• said dual function compensator having a piston disposed in said tubular body for at least initially being disposed in a first position, adjacent to said first end of said tubular body and preventing fluid flow through said tubular body, and moveable to a second position for passing fluid flow through said tubular body;
• said dual function compensator further including a retainer member for selectably securing said piston in said first position, wherein said retainer member is selectable for releasing said piston from being secured in said first position such that said piston is moveable in response to differences in fluid pressure between said interior cavity of said bit body and said flow passage;
• wherein after fluid is expelled from said dual function compensator, said piston is disposed in said second position within said tubular body, located aside of a flow path for passing fluid flow from said interior cavity of the bit body to said flow passage;
• wherein said tubular body of said dual function compensator has perforations extending through the sidewall of said tubular body for providing fluid communication between an interior of said tubular body and said interior cavity, and said tubular body further has apertures extending between said interior of said tubular body and said flow passage for providing fluid communication there-between;
• and
• wherein said apertures, said perforation, said flow passage, and said intermediate space located between the bearing shaft and the rotary cutter are sized for passing drilling fluid.