Sliding rod pump seal - has different rod diameter in middle portion thus varying pressure on O-ring

摘要

The seal is for use with a thrust rod sliding axially between two end positions and into a gas-tight housing containing e.g. sulphur hexafluoride, whose pressure differs from the ambient, having an O-ring of elastic material fitting in a groove in the housing. The diameter of the rod in its central portion is less than that at the ends, so that as the rod slides the O-ring is subjected to variable pressure. This pressure can be high in the end positions and lower in the middle, and the end portions of the rod can merge gradually into the central one. The rod can be honed to reduce friction. The design is particularly for flameproof switch contacts, and reduces friction and consequent heating of the O-ring during rod movement.