Fluorine Rubber (FKM) O-Rings – High Performance Water Resistant Seals

Our FKM O-rings are manufactured in our in-house molding workshop, starting from carefully selected FKM polymer grades. Not all FKM materials perform equally in water and steam; we differentiate our formulations to match actual working conditions. Standard FKM types offer good resistance to ambient and moderately hot water, while specially compounded low-hydrogen FKM grades are deployed for continuous hot water and saturated steam service, to minimise swelling, hardness drop and compression set. We avoid generic off-the-shelf compounds for critical projects, because improper FKM formulation will lead to rapid seal degradation under prolonged contact with hot water or water mixed with additives, detergents and weak acids.

The raw material batches are inspected before production. Each incoming FKM compound undergoes lab testing for hardness, tensile strength, elongation, compression set and immersion behaviour in hot water. This pre-production check helps us eliminate unstable batches before molding begins. Our molding process uses precision CNC machined molds to maintain tight dimensional tolerances, meeting AS568 standard sizes as well as custom non-standard cross-sections and diameters. We control curing time and temperature strictly. Under-cured FKM O-rings swell heavily in water; over-cured parts become brittle and lose elasticity. Our production team adjusts curing parameters according to material grade and part size, aiming to keep compression set low, which is essential for long-term sealing in static and dynamic joints under water pressure.

Water resistance performance is the core feature of this product. FKM demonstrates far better resistance to hot water and steam compared with NBR and many general-purpose elastomers. For cold and room-temperature water, FKM O-rings show very low volume change and stable sealing force. In hot water up to 150°C, properly formulated FKM maintains its physical properties over extended periods. When exposed to saturated steam, the service life depends heavily on temperature and exposure cycles. It is important to note that FKM is not unlimited in steam resistance. At temperatures above 150°C, even premium FKM will gradually degrade, with increased swelling and loss of resilience. For high-temperature steam service above this threshold, we will honestly inform customers about material limits and discuss alternative sealing solutions if FKM cannot meet the service target.

Beyond water resistance, FKM O-rings maintain their sealing function when water carries contaminants. They resist mineral water, tap water with chlorine, weak alkaline water, dilute cleaning agents, hydraulic fluids, lubricating oils and many hydrocarbon solvents. This makes them suitable for equipment that alternates between water flushing and oil operation. Typical application fields include water treatment equipment, high-temperature cleaning systems, steam valves, hydraulic circuits with water-glycol fluids, chemical processing pipelines, automotive cooling circuits and food processing machinery (when food-grade FKM compounds are selected). Our factory can supply FDA compliant FKM grades for applications requiring contact with drinking water or food media.

When compared with other sealing materials, FKM has its own trade-offs. Silicone offers better low-temperature performance but poor resistance to oils and many aqueous chemicals. EPDM has excellent hot water and steam resistance, but cannot withstand oil and hydrocarbon contamination. NBR is cost-effective but fails rapidly at high temperatures and in contact with many solvents. FKM fills the gap where the seal must survive hot water together with oil or chemical exposure. It is not the cheapest option, but it reduces equipment downtime and seal replacement frequency for harsh mixed-media systems.