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Backup Ring

A rigid, non-elastic ring installed adjacent to an O-ring in its groove on the low-pressure side to prevent the O-ring from extruding (being forced) into the clearance gap between mating metal surfaces under high pressure. Without backup rings, O-rings begin to extrude above approximately 7 MPa (1,000 psi) in static applications and 3.5 MPa (500 psi) in dynamic applications, depending on clearance gap and rubber hardness. Materials: PTFE (most common — low friction, chemical inertness, -200 to +260°C), nylon/polyamide (economical), PEEK (high temperature and pressure), and hard rubber (90 Shore A). Types: continuous solid ring (requires stretch over bore — spiral-cut backup ring avoids this), spiral-cut (two-turn PTFE, most popular for field installation), and split ring. Per AS568 and ISO 3601 groove dimensions must accommodate both O-ring and backup ring. For pressures above 14 MPa, use backup rings on both sides of the O-ring. Backup rings extend O-ring pressure rating from 7 to 35+ MPa. Brands: Parker, Trelleborg, Freudenberg.

What you need to know

  • A rigid, non-elastic ring installed adjacent to an O-ring in its groove on the low-pressure side to prevent the O-ring from extruding (being forced) into the clearance gap between mating metal surfaces under high pressure.
  • Without backup rings, O-rings begin to extrude above approximately 7 MPa (1,000 psi) in static applications and 3.5 MPa (500 psi) in dynamic applications, depending on clearance gap and rubber hardness.
  • Materials: PTFE (most common — low friction, chemical inertness, -200 to +260°C), nylon/polyamide (economical), PEEK (high temperature and pressure), and hard rubber (90 Shore A).
  • Types: continuous solid ring (requires stretch over bore — spiral-cut backup ring avoids this), spiral-cut (two-turn PTFE, most popular for field installation), and split ring.
  • Per AS568 and ISO 3601 groove dimensions must accommodate both O-ring and backup ring.

Full definition

A backup ring is a crucial component in sealing applications, often used alongside O-rings to enhance their performance under high pressure. Its primary function is to prevent the O-ring from extruding into the gap between mating surfaces, which can occur when pressure exceeds certain thresholds. In static applications, O-rings can start to extrude above approximately 7 MPa (1,000 psi), while in dynamic applications, this threshold is lower at around 3.5 MPa (500 psi). The risk of extrusion depends not only on the pressure but also on the clearance gap and the hardness of the rubber used in the O-ring, which is typically measured on the Shore scale. For applications involving high pressures, it becomes essential to implement backup rings to ensure reliability and longevity of the seal.

Backup rings are made from various materials, each providing unique advantages. The most common material is PTFE, known for its low friction and chemical inertness, suitable for a temperature range of -200 to +260°C. Other materials include nylon or polyamide, which are more economical, PEEK for high-temperature and pressure applications, and hard rubber with a durometer of 90 Shore A for specific conditions. Backup rings come in several types: continuous solid rings require stretching over the bore, while spiral-cut backup rings, which are generally made of PTFE and are popular for field installation, eliminate the need for stretching. Split rings are also available and can be used in various configurations.

According to standards such as AS568 and ISO 3601, the groove dimensions must accommodate both the O-ring and the backup ring to ensure proper function. In high-pressure situations exceeding 14 MPa, it is advisable to place backup rings on both sides of the O-ring to maintain effective sealing. By utilizing backup rings, the pressure rating of O-rings can be extended significantly, often from the standard 7 MPa to 35 MPa or more, thus enhancing the reliability of the sealing system in demanding industrial applications.

What you need to know

  • What you need to know:
  • Backup rings are critical for preventing O-ring extrusion in high-pressure scenarios, particularly above 7 MPa (1,000 psi) statically.
  • Common material for backup rings is PTFE, offering low friction and a temperature tolerance of -200 to +260°C.
  • Backup rings can extend the pressure rating of O-rings from 7 MPa to over 35 MPa, enhancing sealing effectiveness.
  • Types include continuous solid rings, spiral-cut rings (most common for field use), and split rings.
  • For pressures above 14 MPa, it's recommended to use backup rings on both sides of the O-ring.

Industrial applications

  • 1Used in hydraulic systems where high pressure can cause O-ring failure.
  • 2Applied in pneumatic systems to maintain effective seals under varying pressure conditions.
  • 3Common in automotive and aerospace applications to ensure reliability of seals in critical components.
  • 4Utilized in oil and gas industries for sealing equipment exposed to extreme pressures and temperatures.

Common mistakes

  • ✕Using backup rings in applications below the recommended pressure thresholds can lead to unnecessary costs.
  • ✕Failing to account for the clearance gap when selecting backup rings can result in improper fit and seal failure.
  • ✕Neglecting to verify compatibility of backup ring material with the media being sealed can lead to chemical degradation.
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Pro tip

Always ensure that the groove dimensions are correctly designed to accommodate both the O-ring and the backup ring to prevent seal failure.

Technical standards

  • AS568 - Standard sizes for O-rings and their grooves.
  • ISO 3601 - International standard for O-ring dimensions and tolerances.

Suppliers of seals & gaskets in Mexico

AguascalientesVer Hule Industrial
Ciudad JuárezVer Hule Industrial
Ciudad de MéxicoVer Hule Industrial
GuadalajaraVer Hule Industrial
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Applicable standards

ISO 3601
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