Compressibility goes to heart of what gaskets do. Here we’ll explain what gasket compressibility is and why it’s such an important property of gasket materials.
Compress to Seal
Gaskets are used to seal mating services, particularly between flanges. They take up imperfections in the two surfaces that would otherwise let the fluid being sealed leak out, and accommodate any changes in the gap as might be caused by temperature changes or vibration.
Gasket material works by deforming against the harder flange to take up even microscopic deviations in the surface. Compressibility is a measure of how readily the material does this.
Recovery From Compression
Gasket compressibility goes hand-in-hand with recovery. This is the degree to which the material springs back to its original thickness after being compressed.
Recovery matters because every joint is somewhat dynamic. Whether it’s opened and closed repeatedly, like an access door or panel, or just subject to varying temperatures, loads and vibrations, the effective gap being sealed will keep changing size. To maintain a seal the gasket material must expand and compress with these changes.
Closely related, compression set is when a material doesn’t spring back to its original thickness as the clamping load is removed.
Compressibility Measurement and Specification
The ASTM F36 test provides a standardized way of measuring gasket compressibility. The data needs some interpretation because the test conditions almost certainly don’t replicate your application, but it lets you compare materials.
Compressibility is stated as a percentage of the original thickness. Recovery is given as a percentage of the compression.
Material Selection Considerations
In general, materials that compress readily under light loads lack strength. Open cell foam is a prime example. You wouldn’t use this to seal a pressurized gas or liquid as it would almost certainly fail.
EPDM, neoprene and cork are examples of materials with good compressibility. Higher strength materials tend to have lower compressibility.
Gasket material manufacturers publish ASTM F36 test data, but for advice on a specific application, consult a gasket specialist, like those at Hennig Gasket & Seals.
