The main function of a Backup-Ring is to prevent gap migration under pressure with large gaps. The Backup-Ring prevents this consistently and thus a rapid O-Ring destruction.
Installation is simple and fast. The Backup-Ring is fitted at low pressure side. In case of a double-acting seal two Backup-Rings can be installed on both sides.
The life of the seal is extended. The costs of the sealing system are low: it allows more tolerance of parts to be sealed, thereby reducing the processing cost.
Operation conditions Temperatures of:
–20 °C to +200 °C with FPM
–30 °C to +120 °C with NBR
The function of a PTFE Backup-Ring is similar to that of a Backup-Ring of NBR, but it has a wider range of applications:
Temperatures of –150 °C to +250 °C
With gap extrusion, the material of the O-ring 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-ring can occur.
Back-up rings are used to prevent gap extrusion. Although they do not perform a sealing function, they support the permanent and damage-free sealing function of the O-ring by closing the sealing gap on the side facing away from the pressure.
The material of the support ring 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 choice of material.
Plastics and elastomers such as PTFE, polyurethane or NBR, FPM and EPDM come into question.
Due to the large number of installation spaces for O-rings on the market, the dimensions of the support ring are usually based on the specified installation space geometry.
In wider installation spaces, the assembly is usually carried out on the side facing away from the pressure.
Dimension of the O-ring
The dimension of the groove including tolerances
The type of sealing (external/ internal sealing, static/dynamic)
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.