Enhancing Sealing Performance Under High Pressures
Back-Up Rings
Enhancing Sealing Performance Under High Pressures
Back-up rings are essential components used in conjunction with O-rings in high-pressure sealing applications to prevent O-ring extrusion. These anti-extrusion elements are designed to support the O-ring and allow it to maintain its shape and effectiveness under varying pressures. Back-up rings are made from materials that are harder than the O-rings they support, commonly including thermoplastics like Nylon, PTFE, and PEEK. These materials are chosen for their strength, resistance to deformation, and compatibility with a wide range of fluids and temperatures.
The primary function of a back-up ring is to cover the extrusion gap, minimizing the risk of O-ring damage due to extrusion into the clearance gap between mating hardware components. When a system is subjected to high pressure, the O-ring material can be forced into this gap, leading to material failure and leakage. By placing a back-up ring on the low-pressure side of the O-ring (or on both sides in applications where pressure alternates or comes from multiple directions), the clearance gap is effectively sealed against the high-pressure fluid, ensuring the O-ring remains intact and performs its sealing function effectively.
Back-up rings can be either solid or split. Solid back-up rings are used in static applications where the O-ring and back-up ring assembly is not moved after installation. Split back-up rings, on the other hand, are designed for ease of installation in applications where the hardware configuration does not allow for the use of solid rings. Additionally, contoured back-up rings are available, which have a special profile designed to provide even more effective support to the O-ring and improve the overall sealing capability of the assembly.
The choice between using one or two back-up rings depends on the directionality of the pressure. In applications where pressure is applied from a single direction, a single back-up ring may suffice. However, in applications where pressure may come from both directions, it is recommended to use back-up rings on both sides of the O-ring to ensure optimal protection and sealing performance.
In summary, back-up rings play a critical role in enhancing the sealing efficiency and lifespan of O-ring seals in high-pressure applications. By preventing O-ring extrusion and damage, they help maintain the integrity of sealing systems in a variety of industrial, automotive, and aerospace applications.
| MATERIAL | DESCRIPTION | TEMPERATURE RANGE |
| Unfilled PEEK | PEEK (Polyether Ether Ketone) back-up rings represent an advanced class of polymer solutions for extreme application conditions. Renowned for its mechanical strength, thermal stability, and chemical resistance, PEEK is used in environments where traditional materials fall short. | -70°C to +250°C (-158°F to +482°F) |
| Glass Filled PEEK | Glass-filled PEEK back-up rings incorporate glass fibers into the PEEK (Polyether Ether Ketone) polymer matrix to enhance its mechanical properties and thermal stability. This composite material combines the outstanding characteristics of PEEK with the rigidity and dimensional stability provided by the glass fibers, making it an exceptional choice for demanding sealing applications. | -70°C to +250°C (-158°F to +482°F) |
| DCMS Glass Filled PEEK | Springing opening at the gap after splitting PEEK backups results in rejections and failures should the product be utilized in application. Dynamic Cast Molding System™ (DCMS™) is a proprietary process that lowers inherent stress within the tube, meaning better dimensional stability and less stress. Best of all, it means no springing open at the gap. | -70°C to +250°C (-158°F to +482°F) |
| PTFE | PTFE back-up rings are characterized by their exceptional resistance to chemicals, including most acids, bases, and solvents, making them suitable for a wide range of industries, including aerospace, automotive, and chemical processing. They exhibit minimal friction and are non-sticky, contributing to their effectiveness in applications requiring low frictional resistance. | -200°C to +260°C (-328°F to +500°F) |
| Nitrile | Nitrile back-up rings are designed to complement O-ring seals, enhancing the overall sealing performance in hydraulic and pneumatic systems by preventing extrusion and nibbling of the O-ring under high pressure. Nitrile rubber, also known as NBR (Nitrile Butadiene Rubber), is widely appreciated for its excellent resistance to oils, fuels, and other hydrocarbons, making it an ideal material for back-up rings in applications where exposure to these substances is common. | -40°C to +120°C (-40°F to +248°F |
| Fluoroelastomer (FKM, Viton®) | FKM (Fluoroelastomer) back-up rings stand out for their exceptional performance in severe chemical and thermal conditions. FKM, a class of synthetic rubber designed for high temperatures and with remarkable chemical resistance, is used in applications where other materials might fail. | -20°C to +200°C (-4°F to +392°F) |
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