Back-up rings are manufactured from extrusion resistant material as protection and support elements, normally with a rectangular cross-section.
For static applications they are used together with an elastomer seal – usually an O-ring – placed in the groove.
Because there is a tight fit between back-up ring and bore hole or rod it prevents the O-ring from extruding into the sealing gap under pressure.
Back-up rings
Gap extrusion destroys the O-ring
Back-up ring supports the O-ring
Back-up rings can be used in static applications as well as in translational movements or slow rotations.
If the pressure is one-sided, it is sufficient to install the seal on the side opposite the pressure.
With pressurization on alternate sides, two back-up rings should be used, one back-up ring on each side of the O-ring.
O-ring installation clearance details and recommendations
Pressure direction <->
Pressure direction ->
Pressure direction <->
Back-up ring SUv
– Rectangular profile
– For static and back and forth movements or slow rotations
Back-up ring SG
– Rectangular profile, split
– As alternative to unsplit back-up rings if these cannot be installed or in case a split groove is not possible
– For static and back and forth movements
– Oblique cut at 30° or 45° angles, the back-up ring is cut chipless so that there will be no gap when installed.
Back-up ring SKU
– Concave profile
– Mainly for static applications, possible use in back and forth movements
– Protects the O-ring against extreme deformations during pulsating pressures due to the larger contact surface.
– The form stability of the O-ring has a favorable influence on leak tightness and service life
Back-up ring SKG
– Concave profile, split
– Mainly for static applications, possible use in back and forth movements
– Protects the O-ring against extreme deformations during pulsating pressures due to the larger contact surface.
– The form stability of the O-ring has a favorable influence on leak tightness and service life
– As alternative to the unsplit SKU back-up rings if these cannot be installed or in case a split groove is not possible
Back-up ring SP
– Back-up ring, spiral form
– As alternative to unsplit back-up rings if these cannot be installed or in case a split groove is not possible
– For static and back and forth movements
– Oblique cut at 30° or 45° angles
– Application under large temperature fluctuations
– Large tolerance variations are compensated through spiral contraction and expansion
Back-up ring SUQ
– Special designs made of PTFE (snap-back, quenched)
– Easy installation in enclosed groove areas due to the recovery property of the PTFE material
– Because the dimensions deviate from standard designs, these back-up rings are manufactured only on request based on drawings
O-ring installation groove dimensions for static applications
| cord strength (mm) | droove depth (mm) | w/o back-up ring (mm) | 1 back-ring (mm) | 2 back-ring (mm) | recommended back-up ring width (mm) |
|---|---|---|---|---|---|
| ø d | t ± 0,05 | b + 0,25 | b1 + 0,25 | b2 + 0,25 | |
| 1,50 | 1,10 | 2,10 | 3,10 | 4,10 | 1,00 |
| 1,78 | 1,35 | 2,50 | 3,50 | 4,50 | 1,00 |
| 2,00 | 1,56 | 2,70 | 4,20 | 5,70 | 1,50 |
| 2,50 | 2,05 | 3,30 | 4,80 | 6,30 | 1,50 |
| 2,62 | 2,18 | 3,50 | 5,00 | 6,50 | 1,50 |
| 3,00 | 2,52 | 3,90 | 5,40 | 6,90 | 1,50 |
| 3,50 | 3,00 | 4,40 | 5,90 | 7,40 | 1,50 |
| 3,53 | 3,00 | 4,40 | 5,90 | 7,40 | 1,50 |
| 4,00 | 3,40 | 5,00 | 6,70 | 8,40 | 1,70 |
| 5,00 | 4,25 | 6,30 | 8,00 | 9,70 | 1,70 |
| 5,33 | 4,53 | 6,70 | 8,40 | 10,10 | 1,70 |
| 5,70 | 4,85 | 7,10 | 9,10 | 11,10 | 2,00 |
| 6,00 | 5,10 | 7,50 | 9,50 | 11,50 | 2,00 |
| 6,99 | 5,94 | 8,80 | 10,80 | 12,80 | 2,00 |
| 7,00 | 5,95 | 8,80 | 10,80 | 12,80 | 2,00 |
| 8,00 | 6,80 | 10,00 | 12,50 | 15,00 | 2,50 |
| 10,0 | 8,50 | 12,50 | 15,00 | 17,50 | 2,50 |
Further application information:
The risk of gap extrusion is typical under high pressures or with small ring cross sections in static but also dynamic applications.
A back-up ring must always be used together with an O-ring. The back-up ring itself provides no sealing.
Materials
- TFE pure (CCN-01), standard material
- PTFE + bronze
- PTFE + glass fiber
- PTFE + carbon
- POM, PA, PEEK …
Application limits
> depends on back-up ring material and sealing gap
DYNAMIC APPLICATIONS
- Translational motions: approx. up to 40 MPa
- Rotation: approx. up to 15 MPa
- Operating temperature: -200 °C to +200 °C
STATIC APPLICATIONS
- Approx. up to 250 MPa working pressure
- Speed: approx. up to 2 m/s
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