Sealing Shielding

Racetrack Grooves: Can O-Rings be used in Non-Circular Groove Patterns?

O-seal for racetrack groovesCan O-rings be used in rectangular or non-circular groove patterns? This question comes up weekly, and the answer is a resounding “Yes!” however there are definite guidelines we want to follow. A non-circular face seal footprint might also be called a racetrack groove, a wandering groove or a custom plan view. When using an O-ring, the main design consideration is the corner or smallest radius (shown “r” in diagram). The inside radius should be at least three times the O-ring cross sectional diameter. In a perfect world, six times greater is even better. What we want to avoid is over-stressing the O-ring around the bend, or causing a corner crease which increases likelihood of corner leakage. Designing the radius at six times the cross section will minimize the bending stress, resulting in increased service life.

O-ring in a racetrack groove


Ideal design: r > 6 x W diameter but no less than r > 3 x W diameter

O-ring cross section






To minimize installation difficulties arising from stretch or OD compression on the seal, the centerline perimeter of the groove should match the centerline circumference of the O-ring. The rectangular cross section of the groove will follow the suggested guidelines in the O-Ring Handbook

For those times when hardware real estate is at a premium and we simply cannot increase the inside corner radii to the desired size, an alternative option is the O-Seal. The O-Seal has a round cross section like an O-ring. However the footprint of the O-Seal is designed to match the shape of the groove. The primary advantage of the O-Seal is custom molding to fit the exact groove, eliminating the concern that comes with bending stress at the corners. A smaller corner radii can be used for the groove, allowing the footprint to fit perfectly within the application’s design constraints.

O-seal in racetrack groove

If there are multiple ports or openings on the face, or bolt holes to contour around, these seals can be consolidated into a single O-seal solution. By consolidating seals, the installation process becomes much easier. All seals are ready to be installed at the same time, and the risk of installing the incorrect seal material is eliminated. This may offer the added advantage of streamlining the bill of materials and simplifying the amount of stock to be replenished during the assembly process.

O-Seals are available in nearly every material family and engineered for optimum size and configuration for each unique application. Parker Application Engineers are happy to assist you with your racetrack groove design or a custom O-Seal. Please contact us today via online chat or by email by visiting Parker O-Ring and Engineered Seals Division website.



Dorothy Kern, Applications Engineer Lead, Parker O-Ring Division


This article was contributed by Dorothy Kern , applications engineer lead, O-Ring & Engineered Seals Division




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Comments for Racetrack Grooves: Can O-Rings be used in Non-Circular Groove Patterns?

this is my first time needing to design a racetrack groove. My question is how do I know the size of o-ring to use?
Dorothy Kern
Thank you for the message!
If possible, it is easiest to go with a standard O-ring size. You'll still follow the design principles on Design Chart 4-3 of the O-Ring Handbook. Which means you need to determine either the minimum ID (external pressure) or the Maximum OD (internal pressure) of the seal, and this will get you close to the best O-ring inner diameter. You'll want to measure the perimeter of the groove wall and treat that as a perimeter of a circle to get the O-ring inner diameter. Groove depth will be a function of O-ring cross sectional thickness, spelled out at the bottom chart.
A complete listing of standard O-ring sizes is located in Table 9-1 of the Handbook.
If you want more hands-on help, feel free to call our Applications Engineering team at 859-335-5101, or e-mail us at
How do I calculate compression ratio for square shaped seal.
Dorothy Kern
Thank you for the questions Sakthi,

Calculation for compression on a square-shaped seal is the same as that of a round seal:

(Thickness - Groove Depth) / Thickness
Han Bin
If it is a square shaped seal.How about the r of a racetrack groove. "r > 6 x Width of square-seal but no less than r > 3 x Width of square-seal".Same rule as o ring?
Matthew P
Hi Dorothy,

I know the ID that I need, but how do I know what cross section to choose?

I know it's a function of the smallest radius in the racetrack groove, but what other factors can guide me? Will a small CS perform equally to a large CS, let's say in terms of a box with a lid that's 3 feet underwater.
Is it possible to use racetrack grooves (i.e. oval-shaped) in static seal applications with radial compression? If so, are there any special design guidelines to follow?
Dorothy Kern
Hi Nicolas,
Thanks for reading, good question. I believe you are asking about a radial O-ring in a piston that isn't round, but is more of an oval shape, or maybe even more of a square with rounded corners. If I understand your question correctly, then yes, it is possible. If the piston is more of a square shape than an oval, it is best to keep the radius at 6x the cross sectional thickness (like a face seal). This should not be an issue for an oval piston. Another suggestions is to be aware of the long, straight sections, which may increase the risk of the seal getting pinched or rolling. Lastly, keep an eye on the concentricity of the groove relative to the bore, as you don't want the seal to be unevenly squeezed.
Dorothy Kern
Hi Han,
Great question. I assume when you say "square shaped seal", you are referring to the cross section? If so, then yes, I would follow the same guideline for the corner bend radius as for that of a round cross section seal.

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