Tribological investigation of packing friction along the stem of a valve

A novel valve simulation rig, with a hollow instrumented stem, is used to measure indirectly the evolution of sealing pressure applied by compressed graphite packing as the stem reciprocates. By examining the surfaces of stem and packing after testing by microscopy and EDX, it is possible to define the tribological circuit which controls the behavior of the interface, and hence to explain the physics which underlies the experimental observations. This opens the way to novel and more effective methods for the design of stem seals for low friction and leakage.