PTFE Backup Rings & Anti-Extrusion Rings

Backup rings—also referred to as anti-extrusion rings—are precision-engineered, washer-like sealing accessories installed on the low-pressure side of an O-ring groove. Their fundamental role is to block the diametral clearance gap into which the elastomer O-ring would otherwise extrude under pressure, a failure mechanism responsible for the majority of premature O-ring degradation in high-pressure hydraulic and pneumatic systems. Manufactured primarily from polytetrafluoroethylene (PTFE) and its filled variants, backup rings represent a mature, cost-effective engineering solution for extending seal service life from mere hundreds to tens of thousands of pressure cycles. The operational principle of a backup ring is elegantly simple yet critically important. When system pressure acts upon an O-ring seated in a gland, the elastomer material experiences a hydrostatic force that drives it toward the low-pressure side of the groove. If a clearance gap exists between the mating metal surfaces—typically 0.10 to 0.15 mm in standard industrial assemblies—the O-ring material flows into this gap. With each pressure cycle, this extrusion progresses incrementally, leading to a phenomenon known as nibbling or shredding, where small fragments of elastomer are sheared off by the sharp edges of the clearance gap. Over time, this progressive material loss reduces the O-ring cross-section, diminishes sealing force, and ultimately results in catastrophic seal failure. A properly dimensioned backup ring occupies this clearance gap, providing a zero-clearance barrier that prevents the O-ring from entering the extrusion zone. Engineering guidelines for backup ring deployment are well established in fluid power design handbooks and sealing industry standards. For dynamic (reciprocating) service involving standard NBR 70 Shore A O-rings with typical diametral clearances, a single backup ring is recommended at pressures exceeding 100 bar (1,450 psi). In static (non-moving) applications, the threshold extends to approximately 150 bar (2,175 psi) before a single backup ring becomes necessary. For pressures above 150 bar in dynamic service or above 200 bar in static service—or in any application where pressure direction alternates—dual backup rings, one installed on each side of the O-ring, provide bidirectional extrusion protection. These thresholds assume standard groove geometries manufactured to AS568 or ISO 3601 tolerances. It is important to note that larger clearance gaps, lower O-ring hardness, elevated operating temperatures, and aggressive pressure spikes all reduce these pressure thresholds, often necessitating backup rings at significantly lower nominal pressures. Material selection for backup rings is governed by the specific demands of the application environment. Virgin PTFE offers universal chemical compatibility, an exceptionally low coefficient of friction (0.05–0.10), and an extraordinarily broad temperature range spanning from cryogenic conditions at -200°C to elevated temperatures of +260°C. This makes virgin PTFE the material of choice for chemical processing, food and pharmaceutical applications, and any service where contamination must be eliminated. Glass-filled PTFE, containing 15–25% glass fiber by weight, addresses the primary weakness of virgin PTFE—cold flow and creep under sustained compressive loads. The glass reinforcement increases compressive strength, reduces dimensional deformation under load, and improves wear resistance in dynamic reciprocating service, making it the standard choice for general industrial hydraulics operating in the 150–350 bar range. For the most demanding applications, bronze-filled PTFE with 40–60% bronze content delivers the highest compressive strength and excellent thermal conductivity, enabling superior heat dissipation and dimensional stability at extreme pressures exceeding 350 bar in heavy-duty hydraulic systems. Backup rings are manufactured in three primary configurations to accommodate varying installation constraints and pressure requirements. Spiral-cut backup rings feature a continuous helical cut that allows the ring to be elastically stretched over a piston or collapsed onto a rod without requiring full gland disassembly. This installation flexibility makes spiral-cut rings indispensable for field maintenance, retrofit applications, and equipment where groove access is limited. Solid (uncut) backup rings provide the maximum possible extrusion resistance because the continuous circumferential geometry eliminates any potential leakage path through the backup ring itself. However, solid rings require the gland assembly to be fully disassembled for installation, restricting their use to new equipment designs and the highest-pressure static seals where structural integrity is paramount. Scarf-cut or contoured backup rings employ a single diagonal cut at approximately 45 degrees, striking an optimal balance between installation convenience and sealing performance. The scarf cut allows the ring to be opened slightly for installation while maintaining significantly better gap closure than a spiral cut, making scarf-cut rings the preferred choice for production assembly lines and general industrial hydraulics in the 150–300 bar pressure range. Our manufacturing capabilities encompass all standard backup ring sizes matching AS568 and ISO 3601 O-ring cross-sections, including cross-sections of 1.78 mm, 2.62 mm, 3.53 mm, 5.33 mm, and 6.99 mm for AS568 series, and 1.50 mm, 2.00 mm, 2.50 mm, 3.00 mm, 4.00 mm, 5.00 mm, and 7.00 mm for ISO 3601 metric series. Custom dimensions are manufactured directly from raw PTFE stock without tooling fees, enabling rapid prototyping and economical production of non-standard sizes. All backup rings are produced under ISO 9001 certified quality management systems, with dimensional tolerances held to ±0.05 mm for standard sizes and material certificates of conformance available on request. Lead time for standard sizes is 7–15 business days; custom sizes typically ship within 10–20 business days depending on quantity and material specification.