Støttering NBR

Product group:
STU back-up ring elastomer
AS/BS størrelser
NBR 90

Shape: KAV concave


Operational application limits

The max. permissible operating pressure depends on the gap dimensions.
Temperature (°C): -30 to + 100
The operational application limits use are dictated by the O-ring selected. It is only the resistance of the sealing system to pressure which can be increased by the STU back-up ring.


Hydraulic oils H, HL, HLP as per DIN 51524 Part 1 – 3, mineral-oil based lubricants and greases, non-flammable hydraulic pressure fluids HFA, HFB, HFC as per VDMA 24317 to approx. + 50°C and water to max. + 80°C


The STU back-up ring is a closed ring concave in cross-section. It is produced entirely as a closed ring with no seams, by the injection-moulding process. For our STU back-up rings we use an NBR material of 90° Shore-A hardness, so as to guarantee a high level of resistance to extrusion and abrasion.
The back-up ring’s concave cross-section provides the O-ring with a larger contact surface, having the effect of allowing the O-ring almost fully to retain its circular shape under high pressures and to be less liable to deformation. This means that the shape of the O-ring is supported better and it can therefore withstand higher pressure loads. This produces a better sealing effect and increases the seal’s service life. Due to its closed design, under high pressures it is not possible for the O-ring to be damaged by a sharp edge at the open-ended joint (as is the case with open back-up rings).
The STU back-up ring is of symmetrical profile. This allows it to be used in both internal and external sealing systems.


The groove widths b1 and b2 are presented in the following table:

profile width
S=1.35 mm S=2.18 mm S=3.0 mm S=4.65 mm S=5.99 mm
b1 3.5 – 3.7 4.7 – 4.9 5.8 – 6.0 8.7 – 8.9 12.0 – 12.2
b2 4.6 – 4.8 5.8 – 6.0 6.8 – 7.0 10.2 – 10.4 14.4 – 14.6
S = Ref. H Ref. T
1,35 004-050 1,14 004-050 1,24
2,18 102-178 1,14 102-178 1,35
3,00 201-284 1,02 201-284 1,27
4,65 309-395 1,52 309-395 1,93
5,99 425-475 2,44 425-475 2,97