The Definitive O-Ring Design Guide

Author: Gallagher Fluid Seals Inc.,

What is an O-Ring?

An O-Ring is a donut shaped round ring also referred to as a torus. While O-Rings can be made from plastic materials, or even metal, this reference guide will focus exclusively on rubber, or elastomeric, materials and their unique design and performance considerations. O-Rings are designed to prevent the passage of a liquid or gas. O-Rings work in concert with the gland in which the O-Ring in installed. The gland is typically cut out of the metallic hardware, and there are different types and styles of glands. The gland and the O-Ring work together to seal, and must be designed together for optimal performance.

How does an O-Ring Seal?

Seals prevent fluid from escaping through gaps in mating pieces of hardware. At rest, the O-Ring sits in the middle of the gland. However as the pressure of the sealing system begins to rise the O-Ring shifts to the opposite side of the pressure. Because the material is soft, the O-Ring is mechanically squeezed to block the gap between the two mating hardware pieces. (see image 1) O-Rings must repeat this process over and over again until one of the many failure modes described in this guide will contribute to the O-Ring failure.