Category Archives: Seal Design

Backup Rings

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When the pressure on an o-ring is increased to the point that it can no longer resist being extruded into the diametrical gap, and to compensate for loose fitting components, the use of backup rings to block the diametrical clearance gap and provide support for the o-ring may be a viable solution. A backup ring is made of a harder material than the o-ring itself, but sufficiently resilient to deform under pressure to close the extrusion gap.

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Forces Needed to Compress Seals

One common question concerning static axial seals and gaskets is the amount of force needed to compress them, as it can be a critical design parameter. The amount of force can affect the number, type, size, and spacing of attachments like clips and screws to prevent housing deflection and subsequent leakage.

Testing was conducted using orings of various standard cross sections, materials, and hardnesses. These orings were placed in a universal testing machine and compressed between parallel plates.

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The Importance of Oring Lubrication

Many sealing situations call for the minimization of frictional forces created by a seal. One method of minimizing oring friction is to introduce a lubricant. This lubricant can be of three general types: Internal Lubricant, Temporary External Lubricant, and Semi-Permanent Lubricant Coatings.

Read more to view a plot of insertion and actuation force for AS568-010 orings made from a standard 75 durometer fluorocarbon that has been treated with some common lubricants and inserted into an Aerospace Recommended Practice (ARP)-1233 standard oring groove and bore to show the relative decrease in forces exhibited by the lubricants…

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