Hydraulic Rod Seals (U-Cups)

Hydraulic Rod Seals, commonly known as U-Cup seals, are designed to prevent hydraulic fluid leakage between a reciprocating piston rod and the cylinder gland. They are essential components in hydraulic cylinders, helping maintain system pressure, reduce external oil leakage and support reliable cylinder operation.

U-Cup rod seals feature a U-shaped cross-section with sealing lips that are energized by hydraulic pressure. As pressure increases, the lips are pressed against the rod and housing surfaces, improving sealing contact.

These seals are widely used in mobile hydraulics, construction machinery, agricultural equipment and industrial hydraulic cylinders.

Features & Advantages

• Effective Rod Sealing: Helps prevent hydraulic oil from leaking along reciprocating piston rods.

• Pressure-Activated Lips: The U-shaped profile uses hydraulic pressure to increase sealing contact.

• High-Pressure Capability: Selected polyurethane U-Cup designs can operate at pressures up to 400 bar.

• Wear Resistance: Polyurethane sealing materials provide good abrasion resistance and durability in demanding hydraulic applications.

• Low-Friction Options: Suitable seal profiles and materials help reduce friction and stick-slip during reciprocating movement.

• Multiple Profile Designs: Available in standard U-Cup, asymmetric lip and secondary-lip configurations.

• Standard & Custom Dimensions: Suitable for OEM cylinder production, maintenance and replacement requirements.

Materials & Seal Construction

Hydraulic U-Cup rod seals are commonly manufactured from polyurethane (PU/TPU) and nitrile rubber (NBR), with other elastomer compounds available for selected applications.

Polyurethane U-Cup seals are widely used in high-pressure hydraulic cylinders due to their wear resistance, mechanical strength and resistance to extrusion.

NBR U-Cup seals provide flexibility and compatibility with many mineral oil-based hydraulic fluids. They are commonly used in selected lower-pressure and general industrial sealing applications.

Some high-pressure designs incorporate backup rings made from POM, PA or other engineered thermoplastics to improve extrusion resistance.

Rod Seal Design Options

Standard U-Cup Rod Seals

Feature a pressure-activated U-shaped profile designed for sealing hydraulic pressure from one direction.

Asymmetric U-Cup Rod Seals

Use different inner and outer lip geometries to optimize sealing contact with the moving rod and stationary gland.

Secondary-Lip Rod Seals

Incorporate an additional sealing lip to improve sealing stability and control the lubricating film on the rod surface.

U-Cup Seals with Backup Rings

Combine a primary sealing element with an anti-extrusion support ring for selected high-pressure applications.

Typical Applications

Common applications include:

• Excavators and construction machinery

• Agricultural tractors and hydraulic equipment

• Forklifts and material handling equipment

• Hydraulic presses and industrial cylinders

• Cranes and lifting equipment

• Mining and earthmoving machinery

• Hydraulic cylinder repair and maintenance

Standard & Custom Supply

CORA SEALS supplies hydraulic rod seals in various U-Cup profiles, materials and dimensions for hydraulic cylinder manufacturers, industrial distributors, repair workshops and aftermarket replacement applications.

Standard metric and inch sizes, as well as custom sealing profiles, can be sourced according to technical drawings, samples or existing part numbers.

For quotations, please provide the piston rod diameter, housing groove dimensions, seal profile, material and required quantity. Working pressure, operating temperature, rod speed and hydraulic fluid information are also helpful when selecting the appropriate seal.