Seals are vital for stable hydraulic system operation. Wrong material selection causes leakage and premature aging, leading to costly downtime. Nitrile Butadiene Rubber (NBR), Fluoroelastomer (FKM) and Polyurethane (PU) are the most common hydraulic sealing materials, with distinct performance in temperature, pressure and fluid compatibility.

NBR (Nitrile Butadiene Rubber)

NBR is a cost-effective general-purpose elastomer. It works well with mineral hydraulic oil, offers good elasticity and low compression set, with an operating range of -30℃ to 120℃. It is compatible with water-glycol fire-resistant fluids but cannot withstand phosphate ester media. Ideal for standard hydraulic stations and general machinery using mineral oil.

FKM (Fluoroelastomer)

FKM is a high-performance sealing material, resistant to high temperatures from -20℃ up to 200℃. It excels with mineral oil and phosphate ester hydraulic fluids and has strong chemical and ageing resistance. Its downside is poor compatibility with water-glycol and higher material cost. It suits high-temperature equipment and systems using phosphate ester fire-resistant fluids.

PU (Polyurethane)

PU features outstanding wear and extrusion resistance for high-pressure service, compatible with mineral oil. Its working temperature spans -35℃ to 80℃. PU is vulnerable to hydrolysis in water-glycol and incompatible with phosphate ester. It is widely used for high-pressure hydraulic cylinders and piston rod seals in heavy-duty machinery.

Fluid Compatibility Overview

Mineral hydraulic oil: NBR, FKM and PU are all suitable

Water-glycol fire-resistant fluid: NBR recommended; FKM and PU not recommended

Phosphate ester fire-resistant fluid: Only FKM works; NBR and PU are not applicable

Conclusion

Pick NBR for cost-sensitive, ordinary mineral oil hydraulic systems. Choose PU for high-pressure reciprocating cylinders requiring wear resistance. Select FKM for high-temperature applications or phosphate ester hydraulic circuits.

Factors such as moving speed, extrusion gap and service life should also be considered to prevent early seal failure.