Combination seal and pressure relief valve for sealed drill string unit

摘要

A drill string reamer-stabilizer includes a main body adapted to be connected as an element of a rotary drill string. Individual bearing shafts are mounted axially along the exterior of the main body supporting roller cutters that engage the wall of the borehole. Seal units are positioned around each bearing shaft between each roller cutter and bearing shaft to define a lubricant space. The seal units retain lubricant in the lubricant space and prevent contaminating fluid and materials in the borehole from entering the lubricant space. At least one seal unit comprises an annular cup-shaped elastomer seal member with an annular lip mounted in an annular seal gland in the roller cutter. The seal gland has an inner side adjacent the lubricant space and an outer side exposed to the fluid and materials in the borehole. A ring of compressible filler material fits in the cavity of the cup-shaped elastomer seal member and allows the elastomer seal member to deform so that internal pressure in the lubricant space is vented outward past the annular lip of the seal member but allows external pressure of fluid and materials in the borehole to force the seal member against the inner side of the seal gland creating a fluid tight seal.