Hydraulic O-Ring Solutions
High-performance seals for mobile and industrial hydraulic cylinders, valves, pumps and manifolds.
Overview
NBR 70 Shore A is the correct material for 90% of mineral oil hydraulic systems below +100°C. O-rings remain the most widely used sealing element in hydraulic cylinders, valve bodies, pump housings, and manifold connections because they are simple, reliable, and cost-effective when specified correctly.
At O-Ring Supply Co., we supply hydraulic O-rings in NBR, HNBR, FKM, and polyurethane for applications ranging from general industrial machinery to high-pressure mobile equipment. Our standard hydraulic grade NBR is formulated for 34% ACN content and 70 Shore A hardness, delivering the oil resistance and mechanical strength required for mineral oil-based hydraulic fluids.
Typical Components
Hydraulic Cylinders
Piston seals, rod seals, and wiper seals in single-acting and double-acting cylinders
Directional Valves
Spool seals, port seals, and body seals in directional control and proportional valves
Hydraulic Pumps
Shaft seals, housing gaskets, and high-pressure port connections
Manifolds
Static face seals between machined blocks and cover plates
Mobile Equipment
Excavators, loaders, agricultural tractors, and forestry machinery exposed to dirt and vibration
Recommended Materials
Common Failure Modes & Prevention
Extrusion and Nibbling
Cause: High pressure forcing the seal into clearance gaps without backup ring support
Prevention: Install PTFE or PEEK backup rings above 10 MPa in dynamic service
Compression Set
Cause: Thermal overage or over-compression causing permanent loss of elastic recovery
Prevention: Verify squeeze with a compression calculator and upgrade material if temperature exceeds limits
Abrasion Wear
Cause: Contaminated hydraulic fluid grinding away the dynamic sealing surface
Prevention: Improve filtration to Beta 5 >= 200 and specify harder compounds or polyurethane
Spiral Failure
Cause: Dry running or side loading causing the O-ring to twist in the groove
Prevention: Ensure lubrication, correct piston alignment, and reduce squeeze to 10-12%
Typical Applications
- Hydraulic cylinder seals
- Pump shaft seals
- Valve spool seals
- Accumulator seals
- Hose fittings
- Pressure relief valves
- Filter housing seals
- Manifold seals
Relevant Standards
Frequently Asked Questions — Hydraulics
What is the best O-ring material for hydraulic systems?
NBR 70 Shore A is the standard choice for mineral oil-based hydraulic systems. For temperatures above 100C, specify HNBR. For phosphate ester or synthetic ester fluids, specify FKM.
At what pressure do hydraulic O-rings need backup rings?
Backup rings are recommended above 10 MPa for dynamic seals and above 14 MPa for static seals. They prevent extrusion into the clearance gap under pressure cycling.
What causes O-ring failure in hydraulic systems?
The most common causes are extrusion due to high pressure and inadequate backup rings, compression set from thermal cycling, abrasion from contaminated fluid, and spiral failure from dry running or misalignment.
Are self-lubricating O-rings available for hydraulics?
Yes. NBR and polyurethane compounds can be formulated with internal lubricants such as MOS2 or PTFE to reduce friction and stick-slip in low-lubricity or pneumatic-hydraulic hybrid systems.
Do you supply O-ring seal kits for hydraulic maintenance?
Yes. We supply hydraulic O-ring kits containing the most common AS568 sizes used in cylinders and valves. Custom kits with specific materials and sizes are available for fleet maintenance programs.