Back-up rings are manufactured from extrusion-resistant material as protection and support elements, usually with a rectangular cross-section. For static applications they are fitted in the groove together with an elastomer seal – usually an O-ring. The tight fit between back-up ring and bore or rod prevents the pressurised O-ring from extruding into the sealing gap.

Back-up rings

Data sheet (PDF)

Logos: certified quality, TÜV SÜD, German Federal Ministry for Economic Affairs and Energy, ESF, EU, European Social Fund.

Cross-section of a white PTFE component with horizontal grooves.

Back-up rings made of PTFE and other high-performance plastics

Diagram of the sealing gap with markings p, s and gap.

Gap extrusion destroys the O-ring

Drawing of an O-ring supported by a back-up ring in the groove.

Back-up ring supports the O-ring

Back-up rings can be used in static applications as well as for translational movements or slow rotations.

Cross-section of a seal in a groove with dimensions d1, d2, L and P.

If the pressure acts on one side only, it is sufficient to install the back-up ring on the side facing away from the pressure.

Sectional drawing of an O-ring seated in a groove between two machine parts.

With alternating pressure, use two back-up rings, one on each side of the O-ring.

O-ring installation space details and recommendations

Sectional drawing of an O-ring in a groove with dimensions b, t and Ød.

Pressure direction <->

Sectional view of a seal with dimensions b1, t and ød.

Pressure direction ->

Cross-section of a seal in a groove with dimensions b2 and t and a diameter d.

Pressure direction <->

Back-up rings SU

– Rectangular profile – For static as well as reciprocating or slowly rotating movements

Back-up rings SG

– Rectangular profile, split – Alternative to unsplit back-up rings if these cannot be installed or no split groove is possible – For static and reciprocating movements – Oblique cut at 30° or 45°; the ring is split without cutting so that no gap remains when installed

Back-up rings SKU

– Concave profile – Mainly for static applications, reciprocating movements possible – The larger contact surface protects the O-ring against extreme deformation under pulsating pressure – The dimensional stability of the O-ring has a favourable effect on sealing force and service life

Back-up rings SKG

– Back-up ring, spiral form – Alternative to unsplit back-up rings if these cannot be installed or no split groove is possible – For static and reciprocating movements – Oblique cut at 30° or 45° – For applications with large temperature fluctuations – Larger tolerance variations are compensated by helical contraction or expansion

Back-up rings SP

– Back-up ring, spiral form – Alternative to unsplit back-up rings if these cannot be installed or no split groove is possible – For static and reciprocating movements – Oblique cut at 30° or 45° – For applications with large temperature fluctuations – Larger tolerance variations are compensated by helical contraction or expansion

Back-up rings SUQ

– Special designs made of PTFE (snap-back, quenched) – Easy installation in closed grooves thanks to the recovery property of PTFE – Because their dimensions deviate from the standard designs, these back-up rings are only made to drawing on request

O-ring groove dimensions for static applications

Cross-section (mm) ø d	Groove depth (mm) t ± 0,05	without back-up ring b + 0,25 (mm)	1 back-up ring b₁ + 0,25 (mm)	2 back-up rings b₂ + 0,25 (mm)	recommended back-up ring width (mm)
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
10,00	8,50	12,50	15,00	17,50	2,50

Further application notes:

The risk of gap extrusion is typical at high pressures or with small O-ring cross-sections, in static but also in dynamic applications. A back-up ring may only be used together with an O-ring. The back-up ring itself does not seal.