Compensator for earth boring bits

Abstract

In an earth boring bit of the type having a rotatable cone secured to a bearing shaft, an improved pressure compensating and relief system. A flexible diaphragm has an enlarge peripheral portion in an o-ring configuration sealingly secured in a compensator cavity to form a mud region and a lubricant region. A central portion of the diaphragm has a perforated and ridged protrusion extending into the mud region to form a self energizing area, exposed to the mud region, that seals the perforation when the pressure of the lubricant is less than or substantially equal that of the mud. A wall at the end of the compensator cavity surrounds the mud passage and engages an area around the protrusion when the diaphragm is fully extended by lubricant pressure build-up that exceeds the hydrostatic pressure. Thus, the resulting pressure differential opens the perforation, releases lubricant and relieves the build-up of lubricant pressure. However, the configuration of the protrusion is such as to prevent the entrance of mud into the lubricant reservoir since the exterior area of the protrusion exceeds that of the interior area. The differential pressure to open the perforation is selected to be not less than about fifty psi and the preferred form of the protrusion is substantially cylindrical, its perforation and lubricant entrance being beveled. An absence of metal bonded to the diaphragm helps avoid failures due to stress induce separations and debonding due to chemical attack. Clearances are used between the diaphragm and the end of the cavity and the end of the protector cup to provide self centering with the lubricant and drilling mud passages.