Product Announcement from Freudenberg-NOK Sealing Technologies

How do O-rings really swell in application?-Image

What Customers Want:

Simrit Engineers Develop Design Tool to Accurately Predict O-ring Swell in Application

With millions of dollars in warranty costs and a company's reputation potentially at stake, why do O-ring companies rely on an arbitrary "rule of thumb" to calculate how much a seal will swell in application?

For 60 years, O-ring engineers and customers have accepted the arbitrary rule that a 25 percent volume change is the maximum limit of material swell for O-rings in most applications. To question this rule, and in response to customer and industry demand, Simrit conducted extensive volume swell testing to develop a design tool to accurately predict the swell of O-rings in actual applications.

Out with the Old – Dismissing the "Rule of Thumb"

In the past, when engineers and customers needed to design and select the best O-ring for a given application, they relied on a general "rule of thumb" for anticipating O-ring swell.

The reason behind the rule was basic – engineers analyzed how O-rings behaved when squeezed in the gland and discovered a 75 percent gland fill was typical, leaving 25 percent free gland for thermal expansion and swelling. This rule had never actually been tested or proven, but simply considered conventional wisdom and, therefore, heavily relied on when O-ring customers and engineers designed and selected seals.

But, with so many applications dependent on the technology that seals them, Simrit's technical experts asked: "Why are engineers relying on a general 'rule of thumb?'"

Simrit Changes the Industry

In response to customer and industry needs, Simrit dedicated itself to becoming the first sealing supplier to conduct extensive volume swell testing to establish relationships that can be used to accurately predict the swell of O-rings in applications.

After months of research, Simrit's team concluded that the maximum volume change for O-rings in application was actually 40 percent, not 25 percent. Obviously, Simrit's results showed the old "rule of thumb" was flawed.

Using the initial results as a springboard, Simrit then developed a first-of-its-kind relationship design tool, which could provide the much-needed, accurate linear dimension change information to customers. The design tool, which is now available to all Simrit customers, provides relationship data for any Simrit material in virtually any sealing application.

Simrit's new data – which has been verified by Underwriters Laboratories and proven 88 percent reliable – allows for new thinking about specifications and opens applications to alternative materials. The data eliminates the guesswork in seal selection and allows customers to select the most cost-effective, application-specific seal available.

With this new tool, Simrit customers now have the ability to choose the best seal for their given application, which can, potentially, reduce warranty issues and opens the possible material options for enhanced low temperature behavior, lower cost and better long-term durability.

The Simrit Promise

When Simrit saw the need for more accurate information, it quickly got to work to provide customers and the O-ring industry a better tool. In fact, Simrit's research data has also been used by Underwriters Laboratories when it was seeking input from the industry on the new standards for materials for ethanol fuels.

Underwriters Laboratories used Simrit's data to develop the new limits in their UL157a requirements for gaskets and seals used in handling gasoline / alcohol blends with higher than 15 percent ethanol. This new standard allows for free swell in these fuels of up to 40 percent based on this data and verification testing.

Since its inception, Simrit has dedicated itself to providing the materials, products and technologies that best help their customers. In doing so, the company has developed material and design solutions that have advanced the sealing industry for the past 60 years. For Simrit, replacing a 60-year-old "rule of thumb" with reliable data is all in a day's work!

In Brief

- Simrit has established a first-of-its-kind relationship design tool to predict the swell of O-rings in actual application.

- The new tool was developed in response to customer and industry needs for more accurate real world information.

- Tool and testing results have been verified and used by Underwriters Laboratories.

- For more information, please contact Robert Keller at

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