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The job of an anti-extrusion ring

The job of an anti-extrusion ringO rings perform an essential job supporting various applications.

Creating a tight seal between the two housing parts that hold it, o rings help prevent liquids and gases from escaping from an application, preventing any detrimental harm and defects from occurring.

Therefore, choosing the ring o ring in terms of dimension and compound is essential. And these elements matched with the surface finish of the housing parts will affect the capacity of the ensemble and, therefore, can be the determining factor on whether you will require a backup ring for additional seal support.

Learn more about o ring compounds and various o ring materials suitable for a range of applications here.

When to use anti-extrusion rings 

When we use o rings as seals in applications where pressure levels are high, extrusion of the seal can become a risk factor. i.e., the o ring begins to extrude from the housing, causing physical damage to the seal, making the seal no longer fit for purpose.

This risk can be increased further when the makeup of the o ring is soft, and the play between the two housing parts is large.

Of course, extrusion may not pose too many complications for some applications, and risk may be deemed as low.

However, this is not the case for others, especially those in high-pressure conditions.

Therefore, an anti-extrusion ring will be required to prevent the o ring from moving and causing extrusion in these instances. 

The most common causes of o ring extrusion include: 

  • Incorrect o ring size 
  • Incorrect installation 
  • O ring elastomer and housing surface finish are incompatible 
  • Too much or too little compression. 

Anti-extrusion rings 

Anti-extrusion rings, also known as backup rings, are used in conjunction with o rings in high-pressure applications as this particular type of ring seal provides relative diametrical play and can reduce the level of friction.

To prevent leaks and gaps from occurring, soft and flexible o rings are required; however, this type of material can be prone to pinching, tearing, and being easily pulled from its position. This is where a hard inner ring must be used.

Used alongside o rings to prevent extrusion, an elastomeric rigid seal, anti-extrusion rings hold their shape and position between the two housing units with ease.

This inflexible ring helps to hold the seal to its shape and keeps the rings in their desired place.

For all, we state, inflexible, and anti-extrusion rings are, of course, more rigid; however, they still have a relative amount of elastic, allowing them to deform under stress and close the extrusion gap appropriately. 

The most common anti-extrusion rings are PTFE.

PTFE backup rings include spiral wounds, split, and solid. However, spiral wound o rings are one of the most popular choices because, in an ideal situation, o rings should return to their original form after compression to continue providing a high-quality seal.

PTFE also has the benefit of low friction in dynamic applications. In addition, o ring grooves are enlarged in size so that they can comfortably contain the use of backup rings if required.

Spiral wound PTFE o rings are easier to install; they can often provide a better fit and they help to prevent extrusion.

Anti-extrusion rings are needed when: 

  • Low endurance o rings are installed 
  • For use within hydraulic cylinders 
  • Dynamic applications over 100 bar 
  • Static applications around 950 bar 
  • High-pressure systems 
  • High-pressure valves. 

To find the best backup ring, you must consider ring thickness, inner dimensions of the ring, outer dimensions of the shaft, and radial cross-section of the elastomer.

Benefits of anti-extrusion rings

  • Ideal when you can’t control play between parts
  • Ideal when play is variable due to various working conditions
  • Suitable in elements with large dimensions
  • Allows for minimum reachable pressure inside the system to be achieved
  • No longer do you have to change the types of o rings to suit the application
  • Can support the o ring when stress is increased on the seal
  • You don’t have to change contact surface finishing.

Anti-pressure rings can be used in pairs or individually, depending on your particular requirements.

We would recommend:

For single-acting applications, one backup ring.

For double-acting applications, two backup rings.

As one of the leading professional o ring suppliers in the UK, Specialist Sealing Products provide a vast range of backup rings manufactured from materials to complement a variety of seal types and a range of applications. 

To find the right seal for you and your applications, check out our full range online today. For any queries, questions, or if you would like any further information, please call 01535 274 776 or email your requirements and specifications to sales@specialistsealingproducts.co.uk.

Read the next article: Is fluorosilicone rubber o rings a sustainable choice?

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