SKF
O-Rings and Back-Up Rings
O-rings are the most fundamental static and low-dynamic seals, used extensively in hydraulic systems to seal flanges, fittings, covers, and valve components. SKF supplies O-rings in a wide range of elastomer materials (NBR, FKM, HNBR, EPDM, VMQ) and standard metric/imperial sizes. Back-up rings are anti-extrusion devices made of harder polymers (PTFE, polyamide) that are installed on the low-pressure side of an O-ring to prevent it from extruding into the clearance gap under high pressure. SKF provides matched O-ring and back-up ring sets for hydraulic applications. Proper specification of material and hardness, combined with correct groove design, ensures a reliable static seal that can withstand thousands of pressure cycles without leakage. For high-pressure hydraulic systems, back-up rings are essential to achieving the full pressure rating of the O-ring seal.
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Trusted by Industry Leaders
Universal Static Sealing
Seals flanges, covers, plugs across all hydraulic equipment.
Wide Elastomer Range
NBR (standard), FKM (high temp/chem), HNBR (wear), EPDM (brake fluids), VMQ (high temp static).
High-Pressure Extrusion Prevention
Matched PTFE or PA back-up rings support O-rings up to 1000 bar.
Standard Sizes
ISO 3601 metric and AS568 imperial sizes in stock.
Easy Assembly
Simple groove design; minimal axial or radial installation force.
Cost-Effective
Low component cost, high reliability when correctly specified.
When Back-Up Rings Are Necessary
When system pressure exceeds approximately 100 bar (1500 psi) for standard 70 Shore A NBR O-rings, the elastomer will extrude into the clearance gap and fail. A back-up ring of harder material bridges the gap, protecting the O-ring. SKF provides back-up ring selection data based on pressure, extrusion gap, and O-ring hardness.
Hydraulic O-ring Material Compatibility
Choosing the wrong O-ring material for the hydraulic fluid leads to swelling, shrinkage, or chemical degradation. SKF’s compatibility charts for NBR, FKM, HNBR, EPDM against mineral oils, HFC, HFD, and biodegradable fluids prevent mis-specification and ensure the static seals maintain their integrity.