PTFE back-up rings

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.

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 SU

– 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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