Function of the back-up rings

With gap extrusion, the material of the O-rings can be pressed into the sealing gap on the non-pressure side when the pressure increases and the gap dimensions are large.

If the pressure then increases repeatedly, permanent damage or even complete destruction of the O-rings can occur.

Back-up rings are used to prevent gap extrusion. Although back-up rings do not perform a sealing function, they support the permanent and damage-free sealing function of the O-rings by closing the sealing gap on the side facing away from the pressure.

Materials of the back-up rings

The material for back-up rings must be so hard and extrusion-resistant that it can withstand the pressure that occurs in the application.

Furthermore, parameters such as operating temperature, gap height and resistance to the ambient medium play a decisive role in the material selection of the back-up rings.

Plastics and elastomers such as PTFE, polyurethane or NBR, FPM and EPDM come into question for the bck-up rings.

Installation spaces of the back-up rings

Due to the large number of installation spaces for O-rings on the market, the dimensions of the back-up rings are usually based on the specified installation space geometry.

In wider installation spaces, the back-up rings are usually mounted on the side facing away from the pressure.

Important parameters for the design of the back-up rings

Dimension of the O-rings
The dimension of the groove including tolerances
The type of sealing (external/ internal sealing, static/dynamic)
Pressure
Temperature
Medium

If back-up rings from existing dimension series, such as NBR 90, are used, the design of the installation space must be in accordance with the manufacturer's specifications.

ttv will be pleased to advise you on all questions concerning the selection and installation of suitable back-up rings.

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