The Benefits of a Backup Ring
No matter what type of application you have or who you work for, having a system that will run well for as long as possible should be one of your top concerns.
A backup ring is just one of the many little things you can do to help keep your system running smoothly for as long as possible, along with these other methods. But you might be wondering, just how does it work? There are a few ways a backup ring could improve your system performance and longevity.
Extrusion
O-Rings experience a lot of stress, causing them to wear down in various ways. One of the biggest causes of an O-Ring failure is extrusion, particularly in hydraulic rod and piston seals. Extrusion occurs when the internal pressure of an application becomes too great, causing the O-Ring to extrude – or stick out – into the clearance gap. This extruded or extended portion of the O-Ring will wear down quickly, reducing the amount of material in the O-Ring. After a short period, extrusion results in seal failure.
According to Daemar, some of the common causes of extrusion include:
- Excessive clearances.
- Pressure exceeding system design.
- An O-Ring with an insufficient durometer for the application.
- Degradation of the O-ring due to system fluid.
- Irregular clearance gaps caused by eccentricity.
- Increased clearance gaps due to excessive system pressure.
- Improper machining of O-ring gland.
- Wrong O-ring size installed, resulting in an excessively filled groove.
You should inspect your O-rings for signs of extrusion. Examine the edges of your O-rings on the low pressure or downstream side to see if it appears chewed or chipped. If extrusion has caused your O-ring to fail, you should see small pieces missing from the low pressure or downstream side. In some cases, 50% of the O-ring may have been lost already before the leakage has been found.
Preventing Extrusion
There are three ways to combat extrusion. The first is to reduce the clearances in order to lower the extrusion gap. Unfortunately, this is not practical due to the high expenses involved.
It would be much cheaper to instead raise the durometer of the O-ring. An O-ring with a higher durometer would have a much higher resistance to extrusion, but would also bring two other problems with it: namely, the limited availability of higher durometer materials, and that these materials are not as effective in low pressure applications.
Backup Ring
This brings us to the third option: backup rings. Rather than acting as a replacement for your installed O-rings (as its name suggests), a backup ring is actually meant to work in tandem with the O-Rings you have already installed. Backup rings are typically made of materials with high durometers and resistance to extrusion, including nitrile, Viton (FFKM), or PTFE.
The backup ring is installed between the O-ring and the extrusion gap. The addition of a backup ring will improve the pressure resistance of the O-ring, and prevent it from being forced into the clearance gap, reducing the chances of extrusion and premature seal failure. Depending on the direction of the pressure, you may even be able to install two backup rings. This will provide added protection against extrusion and O-ring failure.
Choosing a Backup Ring
You will have a number of options to choose from to cater an O-ring for your application. They come in two styles: a flat, washer-like style, or a contoured face which provides greater grip and support on the O-ring.
They may also have a solid or spiraled construction. A spiraled construction is made of overlapping rings, providing several different contact levels against the shaft. They provide greater support over solid construction backup rings.
Buy Your Backup Rings From an Industry Leader
From humble beginnings as an O-ring distributor in 1970, Real Seal has grown to become a full-service O-ring supplier and industry leader. Real Seal is not only one of the most technologically advanced O-ring suppliers today; we are also one of the few organizations with a fully-equipped laboratory as well as a full-time chemist and technical staff. This allows Real Seal to meet design challenges special material formulations in a way that no other company can. Don’t wait: give us a call and we’ll provide you with backup rings made to your exact specifications as soon as possible.
