Choosing O-Ring Material NBR HNBR EPDM FKM Or FFKM

Start With The Fluid

Media compatibility eliminates most of the options before temperature is even considered. NBR handles mineral oils and fuels well and is the default for hydraulics. EPDM is the opposite: excellent in water, steam, brake fluid and many chemicals, and poor in mineral oil. Putting EPDM in an oil circuit or NBR in a steam line is the classic early failure.

Then Look At Temperature

NBR is comfortable in normal industrial temperatures but hardens and cracks as the heat rises. HNBR extends that range while keeping the oil resistance. FKM takes higher temperatures again and resists a wide range of chemicals. FFKM sits at the top for both temperature and chemical attack.

FFKM Is A Decision About Downtime

FFKM costs many times what a standard compound costs, so it rarely wins on the seal price. It wins where a failed seal means an aggressive chemical release, a contaminated batch or a shutdown that costs far more than the part. Specify it where the consequence is expensive, not everywhere.

Hardness Size And Surface Finish

Once the compound is chosen, hardness, the groove dimensions and the surface finish of the sealing faces decide whether it works. An AS568 size in the right compound still fails in a groove machined to the wrong depth or left too rough.

What To Send Us

The fluid, the operating and peak temperature, the pressure, whether the seal is static or dynamic, and either an AS568 size or the groove dimensions.