O-ring, 78.97 x 3.53 mm – Viton, Part# 50235

This O-ring sits in a groove between two parts. When you tighten the parts together, the O-ring gets squeezed. It fills up all the tiny gaps. It blocks any path for air or oil to pass through.

The Kinney manuals show this type of O-ring being used on head caps and bearing housings . They always remind you to coat it with vacuum oil before installation.

O-rings are made from a material called nitrile or Buna-N. That works fine for some jobs. But vacuum pumps can get hot. Very hot.

Regular rubber hardens and cracks under high heat. It also swells up when it touches certain chemicals.

Viton is different. Viton is a special type of fluorocarbon rubber. It handles temperatures up to 400°F (200°C) or more . It resists oils, fuels, acids, and solvents.