O Rings Guide

O Rings Guide

O Rings Guide

15 Feb 2015

O Rings Guide
Our O Rings guide will help you understand the key elements to consider if you are responsible for buying O Rings or sourcing custom O Rings. This article is aimed at purchasers and buyers rather than engineers.

What Is An O Ring?

Whichever way you spell it (we don’t mind, but just for accuracy ‘O Ring’ or ‘O-Ring’ is best), an O Ring acts as a seal to keep liquids or gases in or out and lubricants in, dependent on the application. They are called O Rings not because they are shaped in a loop, but because they have a round-shaped cross-section.

O Rings are often referred to as the ‘original seal’ and were first patented in Sweden in 1896 by a Swedish gentlemen by the name of J. O. Lundberg (although it would be 1937 before a patent would be filed in the US by a completely different person).

Since then O Rings have been developed for many varied applications and can cost anything from a few cent to hundreds of Euro/Dollars. The difference in price will be determined by the specifics of the application and how critical the outcome if the O Ring fails. In a small pump, an O Ring failure will cause the pump to seize, with only the inconvenience of replacing the pump. But many will remember the NASA Challenger disaster, where 7 crew members lost their lives because one of the least significant parts in the space craft, an O Ring in the solid rocket booster, failed just after liftoff.

O Rings therefore come in various sizes and thicknesses and are made to withstand pressures ranging from less than 1 PSI to tens of megapascals (thousands of PSI). O-ring seals are commonly made of rubber (typically from one or more of a range of 36 different rubber types and manufactured through one of four methods: extrusion,injection molding, pressure molding or transfer molding), but they can also be made with plastic or metal.

What Is So Great About O Rings?

The amazing thing about O Rings is that they are such a simple solution to what is sometimes a big challenge. They are simple to make and so can be made in huge volumes. Because of this they are inexpensive and reliability can easily be assured when manufactured by quality providers.

Its secret is in the very fact that it is circular in profile. Once in place, typically in a grooved slot, the seal is designed to deform under the pressure, which improves the sealing action. Because of the nature of the most common o ring materials used, a seal can even be maintained where there are small imperfections in the housing, which is ideal in industrial applications where scratches and contaminants can be introduced.

Finally they can be manufactured to any size and specification and a very wide range of materials.

Typical O Ring Applications

O Rings are used in a wide variety of applications ranging from:

  • Hydraulic equipment (using oil pressure)
  • Pneumatic equipment (using air pressure)
  • Typically dynamic applications (equipment with moving parts like pumps with rotating shafts)
  • Can also be static applications, like a flange
  • Where vacuum or low/high pressure environments need to be created/maintained
  • Equipment that run at or operate in high or low temperatures

Sensitive electronic equipment that need to be protected from radio frequency interference

What Are The Key Considerations When Buying Seals?

There are a number of very important things to consider when buying O Rings, here are the most important ones:

  • Speed: The operating speed of the equipment will have a similar impact on the seal as does temperature or pressure. In some cases the smoothness of the surface finish of equipment to be sealed in a high speed application will be very important to avoid excessive wear on the seal or, where the surface is too smooth, causing under-performance of the seal.
  • Pressure: The amount of pressure acting on the seal will be critical to determining the material used. As previously described, a seal is only effective because it deforms. But if the pressure acting against it is too great then there will be excessive deformation leading to extrusion through the mating parts.
  • Media To Be Sealed: Related to the application, it is important to determine the exact media that is to be sealed. Water, chemicals, oil, air, lubricants, etc. all have different considerations and will impact on the material choice.
  • Temperature: Extreme temperatures, whether high or low, will have a direct bearing on the seal material and type. The physical properties of rubber materials mean that at very low temperatures, rubber becomes crystalline in nature (known as the glass transition temperature), while rubber under pressure that is exposed to high temperatures actually contracts rather than expands (known as the Gow-Joule effect). In both cases the sealing properties will be greatly influenced by the type of O Ring material chosen.
  • Dimensions: A relatively obvious consideration, but the important factors are the inner diameter (ID) and the cross section diameter, or thickness. Your engineering team should be able to provide all these to you.
  • Compatibility: Often overlooked, some materials/compounds are not compatible with each other and so those combinations must be avoided. Additionally, where equipment is flushed, the liquids or gases used in this process must also be determined to ensure premature degradation of the seal does not occur.
  • Durometer: In basic terms this relates to the hardness of the chosen O Ring Material. Higher pressure applications will require higher durometers than low-pressure applications.

A note on speed, pressure and temperature:

These three factors are closely related and impact on each other. Therefore ensure these factors are discussed with your seals supplier thoroughly to avoid excessive failure rates.

Abbey Seals International Limited is Ireland’s premier manufacturer of Gaskets and distributor of O Rings and Seals. Established in 1983, Abbey Seals has over 30 years of expertise in gasket and seal applications across virtually every sector and industry, both domestic and international.

Abbey Seals carries 40,000+ variations of O Rings and seals in stock and can assist in the provision of custom O Rings for unique applications.

Our unique approach means that we can have the product you require delivered to your door within hours of ordering; from a single unit to thousands.

Contact Us to find out more about our products or services or to place an order.

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