How Do You Choose O-Rings?

Apr 26, 2020

If you find yourself in a position where you have developed an application that requires seals, you need to ensure that you make the right choice. Finding the correct seals is imperative to the success of your application and as a result, choosing the correct O-Ring should never be underestimate. Along with this, the demands of that application will determine how you select your O-rings.

You should consider performance and durability as well as reducing the risk of failure when selecting O-Rings. However, choosing O-Rings will be determined by several factors and that is what we will aim to cover here.

Choosing O-Rings Material

To select the correct O-Ring, you will need to ensure that you choose the right material, ensuring it is compatible with all media that are working within your application. Therefore, if one of the following factors are considered incompatible then this can have a negative impact on the ring and how it performs.

Operating Fluid – The operating fluid that you use can chemically cause the seal material to degrade. Therefore, the wrong compound and fluid incompatibility can cause the O-Ring to swell. This will result in poor performance and it could even cause it to fail.

Temperature – Temperature can cause significant problems for your O-Ring and how it performs. It is important to keep the temperature within the optimum working parameters because should the temperature drop too low, it can cause the O-Ring to become brittle and lose its elasticity. In contrast to this, if the temperature is too high then this can cause significant degradation that could prove catastrophic.

Operating Pressure – The operating pressure is something that you need to seriously consider. Where a static sealing application is used and when other factors are taken into account, it is usually fine to use a standard 75 shore hardness material as this will usually be sufficient enough for the job. However, once the pressure increases to around 1500 psi, you should think about utilising a backup ring as a way of preventing extrusion. Along with this, it is important to consider a shore hardness of around 80-90.

Housing Design or Seal Grove? 

The performance of the O-Ring is underpinned by the seal housing surface being finished as well as the finish of the mating surface. This is down to the fact that a variation in extremes of smoothness and roughness will not result in a satisfactory sealing. If the surface is rough, then this could cause small cuts to appear in the O-Ring and this will cause it to degrade to the point where it fails and does not last as long as expected. In contrast to this, if the surface is especially smooth, then it can cause an aqua-plane effect and that can lead to leakage.

Therefore, a good guideline to follow is to use a seal grove surface finish of 1.6 Ra for sealing gases and as much as 3.2 Ra for sealing fluids and dynamic applications as this can help to reduce abrasion and the spiralling potential.