It may seem logical that compressing an o ring more tightly would improve its sealing ability. In practice, excessive compression can create problems, especially in applications involving repeated movement.
O ring compression, commonly called squeeze, is the amount by which the ring's cross-section is compressed when installed in its groove. It creates the initial contact needed for sealing, but the required amount depends on the application.
Why Does an o ring Need Compression?
An o ring is made from an elastic material. When installed, it is compressed between the mating surfaces, creating contact pressure that helps prevent fluid or gas from passing through the sealing interface.
The amount of compression is influenced by the o ring cross-section, groove depth, manufacturing tolerances, and material properties.
If compression is insufficient, the ring may not maintain adequate contact under the operating conditions. This can lead to leakage, particularly when pressure is low or the components move relative to each other.
However, increasing compression indefinitely is not a reliable solution.
Static and Dynamic Applications Have Different Needs
A static o ring seal is used between components that do not move relative to
each other during normal operation. Examples include flange connections, covers,
and stationary pipe fittings.
A dynamic o ring seal operates between moving components, such as a piston and cylinder or a reciprocating rod.
Dynamic applications require careful control of friction. Excessive squeeze increases contact pressure and can raise friction, operating temperature, and wear. In reciprocating applications, it may also contribute to irregular movement or damage to the ring.
This is why static and dynamic o ring glands should not automatically use the same compression design.
Groove Space Matters Too
Compression is only part of the design.
Rubber is nearly incompressible in volume. When an o ring is compressed, its material needs room to move within the groove. If the groove is too small or excessively filled, the material may have nowhere to expand.
Temperature increases and fluid-induced swelling can make this problem more serious. An overfilled groove may increase friction or create conditions that contribute to extrusion and premature failure.
A suitable design therefore considers both squeeze and gland fill, together with the expected dimensional tolerances and operating environment.
What Should Engineers Consider?
Before choosing an o ring or designing its groove, review:
Whether the application is static, reciprocating, or rotary.
The o ring cross-section and material.
Groove depth, width, and tolerances.
Operating pressure and temperature.
Fluid compatibility and possible material swelling.
Required movement, friction, and service life.
Design recommendations should be taken from the relevant manufacturer's engineering handbook or an applicable standard. A single squeeze percentage should not be applied to every o ring application.
Good o ring sealing is not achieved by maximum compression. It comes from providing the correct deformation while leaving enough space for the material to function under real operating conditions.
