Custom O Rings: What You Need To Know

O-rings have been around for a very long time, existing in one form or another since the beginning of the twentieth century. But they are still extremely useful today and, with advancements in materials and technology, plus the common use of custom O-rings, they are probably more widely used and important than ever.

Understanding Standard O-Rings vs. Custom O-Rings

O-rings, as the name suggests, have a circular or doughnut shape and are a type of gasket that is designed for high pressure environments. They are generally positioned in a groove or channel between two components that will be pushed together. The aim of the O-ring is to form a prefect seal when this happens so that gases or liquids do not leak out.

O-rings are usually made from some type of elastomer, which is distorted as pressure is applied so that the seal is formed. Many types of standard O-ring are available for a wide range of general applications. However, custom versions are the only practical choice for specialist uses — when components are of a non-standard shape or size, when excessive pressures or temperatures need to be handled or where applications have very demanding specifications and failure is not an option.

Key Factors for Custom O-Ring Design and Selection

To choose the most suitable O-ring, you must fully understand your application and its demands. If the O-ring is to be subjected to extreme temperatures or pressure, or is to be exposed to harsh chemicals, this will affect the material used and the construction of the O-ring.

One of the main factors when choosing is whether a static or dynamic seal is required. A static O-ring is intended to be used between two surfaces that do not move relative to each other while a dynamic version forms a seal between moving parts.

Static O-rings generally need to be less robust and hard-wearing than dynamic versions, although unnecessary abrasion from components should be avoided. Dynamic O-rings also require more lubrication to operate efficiently.

Material Selection is Paramount

O-rings are available in a variety of materials and choosing the best one will ensure your custom O-ring operates at peak efficiency. Different materials will have varying ability to deal with chemicals, extreme temperatures and pressure ranges:

• Nitrile is a popular material because it is general purpose and is robust so is suitable for demanding roles. It resists petroleum, propane and some hydraulic fluids but can be damaged by halogenated hydrocarbons, brake fluids and certain hydraulic fluids, and cannot handle high pressure or temperatures above 120⁰C.
• Rubber is the most common material and is used in applications that are not too demanding.
• Viton is made from fluorocarbon rubber and is widely used as an alternative to nitrile, with strong chemical resistance and a working temperature of -26 to +205⁰C. However, in dynamic applications at below -15⁰C, the material can become inflexible and is prone to failure.
• Silicone is often used in outdoor applications due to good weathering and heat resistance, with temperature ranges from -50 to +200⁰C. This material has low tensile strength although compound grades have better tear resistance.

Some materials are classed as food grade and so can be used in the catering industry while other O-rings are made from hybrid materials and are used in high performance engines.

Dimension and Sizing

One of the advantages of using a custom O-ring is that, unlike a standard model where the size may be only approximately right, you know it will be a perfect fit.

• The O-ring diameter will be the right size for the groove or channel into which it fits.
• The cross-section size affects the compression, so needs to be correct for the right sealing performance.
• The O-ring will undergo a degree of stretch when in the groove or channel and this must be allowed for.

Application Environment

To function correctly, an O-ring has to deform predictably and uniformly in its groove when pressure is applied. However, this will depend on the temperature and other challenges from the application’s environment. You therefore need to be aware of all the environmental challenges and choose a material and type of O-ring that will handle them.

Whether the application is static or dynamic will determine the sealing requirement, as will the design of the groove or channel in which the O-ring is placed. The component part’s surface finish will affect the performance of the O-ring and in some cases lubrication may be needed to reduce friction. The main environmental factors, however, are normally the operating temperature, the pressure applied and the type of liquid or gas the O-ring has to deal with.

Advantages of Choosing Custom O-Rings

Standard O-rings are generic products that are mass-produced for general use. Although different ranges are available, with varying sizes, materials and capabilities, they are still limited in what they can do.

If you have a specialised application that processes liquids or gases at high temperatures and under extreme pressure, a standard O-ring is unlikely to be able to withstand the conditions imposed on it. Certain industries, such as aerospace and automotive manufacturing, are very demanding and require very precise and reliable performance, often under very harsh conditions. A custom O-ring will provide the assurance that it will work reliably at all times because it is designed to meet specific challenges.

The Custom O-Ring Manufacturing Process

The method of manufacturing for an O-ring will, to some degree, depend on the material it is made from. However, they are generally manufactured using moulding techniques such as injection moulding, compression or transfer. Certain applications, such as for medical equipment, may require manufacturing in clean room conditions while food production needs compliant materials.

Common Applications for Custom O-Rings

The versatility of O-rings means they are used in various industries. Their ability to withstand high temperatures and extreme pressure for several liquids and gases makes them an ideal choice.

O-rings are used in pumps, connectors, valves and cylinders. As a result, they’re commonly used in automotive vehicles, oil and gas pumping operations and for any industry where a reliable seal is essential.

Tips for Specifying Custom O-Rings

The most crucial factor when specifying a custom O-ring is anticipating how it will be used. Be aware of maximum temperatures and pressures, of the nature of gas or liquid being processed and the regulations that need to be complied with.

Take note of the size of the groove and the way the O-ring needs to behave. To ensure your O-rings perform as they should, work with a specialist o-ring supplier to get the specification right. Contact us and we will be happy to help.