How to Use O-Rings?

Over the past 120 years or so, the field of engineering, manufacturing and component design has changed so radically that O-rings have remained more or less the same in form and function. Some of the materials used to make O-Rings have certainly become more high-tech over time, but in essence, O-Rings remain a simple and reliable solution to a problem first posed more than a century ago.

In this guide, we will discuss how and when O-rings are used and what the differences are between static and dynamic O-ring seals.

How do O-rings work?

Whether sold individually, wholesale in large quantities or - increasingly common - as part of a highly flexible line of O-ring kits, O-rings are usually the same in basic form and function.

As implied, their name refers only to the classic doughnut or ring shape, and they exist purely to create a better, more leak-proof seal between two other components, often with the aim of preventing accidental leakage of gases or liquids. In this sense, they are actually a type of gasket - the main difference being that O-rings are more commonly used in high-pressure environments where ordinary cork, paper or rubber gaskets may be prone to failure.

O Ring

In very basic terms, O-rings work by being located in a groove or channel between two surfaces/components that are to fit or be pushed together. O-rings, usually made of some form of elastomer, are located at the joint between these two parts and are compressed to help form a tight seal.

The greater the internal pressure applied to this joint, the greater the deformation of the O-ring within its groove, which can increase its overall sealing force to a certain point - but beyond a certain pressure or under more dynamic working loads, this can lead to a failed seal. It is important to strike a balance between O-ring material, size and operating environment to perform the tasks you need it to perform.

How to Use O-Rings?

O-rings are common in pumps, cylinders, connectors, and valves and help seal connections between components and prevent fluid and gas leakage. They are used with static, dynamic, hydraulic and pneumatic components, making them a particularly versatile solution to a very common engineering problem.

As mentioned above, you use an O-ring in a very similar way to any other type of gasket: an elastomer-based circular cross-section sits in a specially designed groove (its geometry is fairly universal), and once assembled and interlocked, it is compressed between two or more parts. The resulting O-ring seal is economical and reliable, relatively resilient, and easy to maintain/replace when needed.

O Ring

One of the main advantages of an O-ring type seal is that it returns to its original shape after the part to which it is attached is disconnected and the compressive force acting on it is removed. Over time, repeating this process will begin to have an effect on the elasticity and uniformity of the material and the shape of the seal, eventually requiring a new O-ring if the seal is to be maintained.

Under pressure, the O-ring will move in its groove toward the low pressure side of the seal, forcing it tighter and tighter against the inner and outer walls of the gland formed between the two components. To some extent, this will produce an increasingly tight seal, but it is important not to apply more pressure to the O-ring than it is designed to withstand, as too much deformation will eventually cause the seal to start leaking again.

What is the difference between static and dynamic O-Ring seals?

Static and dynamic O-Ring seal designs differ in several key ways. A static O-Ring is any O-Ring designed to make contact with two or more surfaces that do not move relative to each other, while a dynamic O-Ring is an O-Ring that helps create a seal between moving parts.

In general, static O-rings are made of materials that are not as rugged as dynamic O-rings. It is also important that the components joined together in a dynamic environment are carefully designed and finished so that they do not wear, shear, and eventually break the O-ring that lies between them. This is not an issue for O-rings used in static applications, as the only stress they are subjected to is usually compression (they tend to be quite elastic).

While all O-rings require some degree of lubrication for optimal performance, dynamic O-rings require heavier and more frequent lubrication (and more regular inspection, maintenance, and replacement) than static versions. Different types of dynamic motion - for example, rotating, reciprocating and oscillating - require O-rings manufactured with different material qualities to achieve optimum levels of performance.