Back up rings from manufacturer ➤ Prevention of gap migration

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.

As with the O-rings, it is important that the back-up rings are precisely matched to the specific application conditions. This applies to sealing materials for hydraulic couplings in the form of back-up rings as well as back-up rings for idlers.

Here you will find a brief overview of common materials and their characteristic properties:

Back-up rings PTFE

Most back-up rings are made of PTFE. PTFE back-up rings, also known as Teflon back-up rings, are characterised by their almost universal resistance to media. However, their properties in terms of durability and elasticity are limited.

NBR back-up rings

Many back-up rings are made of NBR or nitrile rubber. This elastomeric material is particularly suitable for sealing machine parts against lubricating oils and hydraulic oils. However, NBR back-up rings are only slightly resistant to ageing, UV radiation and high temperatures (over +120 °C).

FKM back-up rings

An FKM back-up ring is ideal for applications at extremely high temperatures, as this material can withstand temperatures of up to +200 °C. In addition, these back-up rings are resistant to many strong acids and bases, but not to hot water or steam. When selecting back-up rings, it is therefore important to consider the specific properties of the materials with regard to the respective application.

Other suitable materials for back-up rings are plastics and elastomers such as polyurethane, FPM and EPDM.

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.

Structure and use of support rings

The back-up rings are robust protective elements made of an extrusion-resistant material that typically have a rectangular cross-section. In static applications, they are used together with an elastomer seal. This is usually an O-ring selected according to size.

The precise fit between the back-up ring and the bore prevents the pressurised O-ring from entering the sealing gap. This arrangement ensures a reliable seal and protects against undesirable material effects.

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.

Frequently asked questions

Where and why are back-up rings used?

Back-up rings from ttv are used in a wide variety of industries and applications where seal protection is required to prevent gap extrusion. This can increase the service life of the seals and make the overall system safer.

O-rings are used in many different machine components. Back-up rings help to protect the O-rings against gap extrusion, which is increased by high pressures and temperatures.

Back-up rings are used in fittings and valve technology to prevent leaks and extend the service life of the seals.

What types of support rings are there?

Back-up rings can be divided into two basic categories: active and passive.

Active back-up rings are pressed both axially and radially by the seal in the direction of the sealing gap and cover it completely. They act actively by forming a barrier against penetration under pressure into the sealing gap. On the other hand, passive back-up rings lie parallel to the seal and are pressurised axially. Their task is also to cover the sealing gap and prevent extrusion of the sealing material. The choice between active and passive back-up rings depends on the specific requirements of the application, and both variants help to optimise the compressive strength of the sealing system.

Why is a back-up ring indispensable as protection for an O-ring?

A back-up ring is indispensable as it makes a decisive contribution to increasing the compressive strength of a sealing system. In combination with an O-ring, the back-up ring not only provides an effective seal, but also protects the O-ring from gap extrusion. This gap extrusion occurs when the sealing material is pressed into the sealing gap under high pressure, which can lead to damage and ultimately to the failure of the sealing system. The back-up ring therefore acts as a protective shield here, minimising these undesirable effects and thus ensuring the longevity and performance of the entire sealing system.

Why should I choose support rings from ttv?

Quality: We use high-quality materials and manufacture our back-up rings according to strict standards. We also carry out comprehensive quality checks to ensure that we can supply our customers with technically flawless products.

Personalised customer service: We personally support our customers with our team of experts. Throughout the entire project process, from product consultation to dispatch.

Short delivery times: As a manufacturer in Germany, we can guarantee you short delivery times. Please contact us to discuss the details in person.

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