Hydraulic Rod Seals

Hydraulic rod seals are installed in the cylinder head and seal the dynamic interface between the reciprocating rod and the stationary gland. Their primary function is to retain pressurized hydraulic fluid inside the cylinder while allowing a controlled lubricating film to return on the retract stroke. A well-designed rod seal minimizes leakage to the atmosphere, reduces friction and wear on the rod surface, and protects downstream piston seals by maintaining proper oil film thickness. The most common rod seal profile is the U-cup, named for its U-shaped cross-section. The flexible lips energize under system pressure to increase sealing force as pressure rises. UN is the metric standard U-cup used on rods in general industrial and mobile hydraulics. UHS and UPH are higher-performance variants with optimized lip geometry for higher pressure and lower friction. For demanding low-friction or high-pressure applications, PTFE-bronze step seals and Glyd rings are used as primary rod seals. These composite seals use a PTFE sealing ring energized by an O-ring or X-ring to achieve extremely low friction and high extrusion resistance. They are common in servo cylinders, injection molding machines and presses where precise positioning and stick-slip-free motion are required. Our rod seal range covers rod diameters from 6 mm to 400 mm in TPU, NBR, FKM and PTFE-bronze materials. Standard profiles include UN, UHS, UPH, FA, J and step seals. For each application we select the material and profile based on pressure, speed, fluid compatibility, surface finish and operating temperature. Custom sizes and special lip designs are manufactured from drawing or sample.