Patent ID: 7673705

Claim:
An isolated pressure compensation system for a Measurement-While-Drilling Tool, comprising: a pressure balance chassis; a circumferential relief on the exterior surface of the pressure balance chassis; a pliable cylindrical bladder circumferentially surrounding the relief, and forming a pressure compensating reservoir; a pair of clamps, circumferentially sealing the bladder to the pressure balance chassis above and below the pressure compensating reservoir; an interior bore extending through the center of the pressure balance chassis; a pressure balance rod slidably located in the interior bore; an enlarged cylinder portion formed on the interior bore; a fluid passage between the reservoir and the cylinder portion; a piston formed on the pressure balance rod, the piston being axially slidable within the cylinder portion of the pressure balance chassis, and being located interior of the pressure compensating reservoir; a piston seal located on the piston, providing a fluid seal between the piston and the cylinder bore; an actuator chassis connected to the pressure balance chassis, forming the upper end of the cylinder portion; a motor-electronics chassis connected to the upper end of the actuator chassis; a rod seal, providing a fluid seal between the pressure balance rod and the actuator chassis; the bladder being exposed to drilling fluid external to the MWD Tool; wherein drilling fluid pressure acting on the bladder is transferred to a fluid pressure acting on the piston; and, wherein upon disconnection of the motor-electronics chassis from the actuator chassis, the fluid in the compensating reservoir remains sealed.