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Back-up Rings
Parco makes back-up rings (hard rubber, contoured back-up rings) for use with O-rings in high-pressure applications.
Pressure applied evenly to both sides of a seal normally has no effect on sealing performance. When a pressure difference is anticipated, elastomer selection must also consider differential pressure resistance. High differential pressures will cause improperly specified O-rings to extrude, resulting in seal damage and eventually failure.
Standard O-ring groove and gap dimensions cited in MIL-G-5514 and AS4873 generally provide adequate sealing for differential pressures to 1500 psi for all elastomers. Substantial improvement in extrusion resistance is attainable by 1) using harder O-rings, 2) decreasing the diametral clearance, or 3) using contoured hard rubber or plastic back-up rings. O-rings with high modulus and hardness are better able to resist extrusion. The higher the modulus of a material, the greater the force required to stretch it. Similarly, the harder the material, the greater its resistance is to indentation.
The following graph indicates conditions that result in O-ring extrusion with and without back-up rings.
Below is a list of our popular compounds for back-up rings. If you have any questions about our back-up rings, feel free to e-mail our sales staff at sales@parcoinc.com. You may also contact a Parco customer service representative at (909) 947-2200.
| Compound | Elastomer | Color | Description |
2067-90 | Nitrile | Black | 90-durometer nitrile; extrusion and abrasion resistant; high pressure resistant. |
Nitrile | Black | Low cost; general purpose; 90-durometer nitrile. | |
9009-90 | Fluorocarbon | Black | 90-durometer fluorocarbon; high-temperature resistant; AMS 7259 and AMS R 83248 and MIL R 83248 compliant; QPL-listed. |
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