Table of Contents
General Groove Guide
There are many variables that go into properly designing an O-ring groove. This page is intended to serve as a guide for how to use all of these variables to formulate the best O-ring sealing assembly possible.
Please keep in mind that every O-ring application is different and that there are always exceptions to rules. These are general considerations. When determining exact O-ring groove dimensions, it is also wise to see our more specific O-ring groove design tables.
If you have any questions or if you need assistance with engineering design, please feel free to get in touch with our engineering team.
O-Ring Inside Diameter - Stretch & Interference
When O-rings are used in O-ring sealing applications, there will almost always be some stretch (the ID of the O-ring is smaller than the ID of the gland) or interference (the OD of the O-ring is larger than the OD of the gland).
Depending on the O-ring application, different levels of stretch and interference are recommended.
Relevant Equations
General Recommended Values *
-
Face Seal (Internal Pressure): 0-3% Interference
-
Face Seal (Internal Vacuum): 0-5% Stretch
-
Rod (Static): 0-2% Interference
-
Piston (Static): 0-5% Stretch
* Please keep in mind that recommended O-ring stretch and interference values can vary depending on the application. Please see our O-ring groove design tables for more specific recommendations, or get in touch with our engineering team.
O-Ring Cross Sectional Diameter - Small VS Large
Depending on the cross sectional diameter (CS) of an O-ring, the behavior of the seal can vary significantly.
Larger O-ring seals tend to be more effective in environments with frequent encounters with granular contaminants, such as dirt or dust.
Smaller O-ring seals tend to be more effective in environments that encourage explosive decompression.
Regardless of what O-ring size you need for your application, TKF Tech will be there to support your needs!
* Particularly true for Fluorocarbon Elastomers & Nitrile Elastomers. Less applicable to EPDM and Silicones.
** Applies to the tensile strength and elongation of Nitrile Elastomers. Also applies to the elongation of Fluorocarbon Elastomers.
*** Can vary depending on O-ring sizing standard and popularity.
Please see our O-ring groove design tables for more specific recommendations, or get in touch with our engineering team.
Gland Corners
One of the most common O-ring failure modes is damage caused during installation. To avoid O-ring installation damage, it is important to eliminate burs or sharp surfaces that may interact with the O-ring seal.
By replacing any sharp corners with Chamfers or Fillets, most O-ring damage can be avoided.
Additionally, a lack of sharp corners will help prevent the O-ring from being damaged by the groove shifting during use or by high pressures.
Please see our O-ring groove design tables for more specific recommendations, or get in touch with our engineering team.
Friction
When designing dynamic O-ring sealing applications, Friction is often one of the most important variables. For example, if the friction is too high on the O-ring seal of a hand operated syringe, it may be too difficult for the user to actuate. Inversely, if the friction is too low on an O-ring valve assembly, it could mean that certain components don't hold together predictably while in motion.
* This is a minor factor and should typically be ignored except for ultra high speed applications.
Please see our groove design tables for more specific recommendations, or get in touch with our engineering team.
Gland Surface Finish
When designing an O-ring sealing assembly, it is important that the sealing surfaces have the proper finish. If the finish is too rough, the O-ring sealing material might not be able to completely fill all surface voids which can lead to leaks. A lower durometer O-ring sealing material can help fix this problem by flowing more easily into surface voids.
Additionally, rough surfaces can damage O-ring seals, especially in dynamic O-ring applications. Sometimes it is best to use a harder, more abrasion resistant O-ring sealing material to help slow the effects of dynamic friction damage.
General Recommended Values *
-
Static Seal (Liquids): 32 RMS
-
Static Seal (Vacuum and Gases): 16 RMS
-
Rod & Piston (Dynamic): 16 RMS
* Please keep in mind that recommended surface finish values can vary depending on the application. Please see our O-ring groove design tables for more specific recommendations, or get in touch with our engineering team.
O-Ring Compression
When O-rings are used in sealing applications, there will almost always be some compression. Without sufficient O-ring compression, the surfaces of the O-ring sealing material would not mate properly with the gland surfaces, likely causing loss of sealing performance.
Depending on the application, different levels of O-ring compression are recommended.
Relevant Equations
General Recommended Values *
-
Face Seal: 10- 25 -35% Compression
-
Rod & Piston (Static): 5- 20 -30% Interference
* Please keep in mind that recommended O-ring compression ratio values can vary depending on the application and O-ring materials used. Please see our O-ring groove design tables for more specific recommendations, or get in touch with our engineering team.
Gland Fill
When O-rings are compressed into closed glands, the O-ring sealing material deforms and fills a certain percentage of the volume of the groove. If the gland fill is too high, the O-ring can be damaged during assembly by the O-ring material swelling when contacting chemicals, or even by thermal expansion.
Depending on the application, different levels of O-ring gland fill are recommended.
Relevant Equations
General Recommended Values *
-
Static Seal: 65- 75 -85% Gland Fill
* Please keep in mind that recommended O-ring gland fill values can vary depending on the application and materials used. Please see our O-ring groove design tables for more specific recommendations, or get in touch with our engineering team.
O-Ring Gland Concentricity
When O-rings are used in pressurized or vacuum Rod & Piston O-ring sealing assemblies, it is important to maintain a relatively consistent seal compression across the entire O-ring.
In a perfectly Concentric sealing assembly, the clearance and O-ring seal compression would be constant across the entire assembly. In a Diametric sealing assembly, the compression of the O-ring seal and clearance would vary.
A diametric O-ring model is more realistic because it is technically impossible to achieve a perfectly concentric O-ring model. If a diametric O-ring sealing assembly is too unbalanced, it can cause leaks. If the Diametral Clearance is too large, the O-ring seal can experience extrusion.
Please see our O-ring groove design tables for more specific recommendations, or get in touch with our engineering team.
Diametral Clearance = A + B
O-Ring Extrusion & High Pressure Applications
When O-rings are used in high pressure sealing applications, there is increased risk of extrusion. Without sufficient O-ring seal protection or proper O-ring gland design, the O-ring seal can be irreversibly damaged. Harder O-ring materials and Backup Rings typically produce a more extrusion resistant system.
Depending on the pressure levels, smaller O-ring clearance levels may be recommended.
Please see our O-ring groove design tables for more specific recommendations, or get in touch with our engineering team.
Backup Rings
Backup rings are crucial components in O-ring sealing systems, providing enhanced support, reduced friction, and improved O-ring sealing capabilities. Backup rings prevent extrusion of the O-ring under high-pressure conditions and maintain a secure O-ring seal even at elevated pressures. In dynamic O-ring applications, backup rings reduce friction between the O-ring and mating surfaces, minimizing wear and ensuring longer-lasting O-ring sealing performance.
Additionally, backup rings help maintain the correct O-ring compression and ensure proper seating of the O-ring, optimizing O-ring sealing efficiency and preventing potential leaks. Using one backup ring on either side of the O-ring helps protect the seal against dynamic pressures in both directions. Overall, backup rings play a vital role in improving the reliability and efficiency of O-ring sealing systems in various applications, providing engineers with peace of mind in critical O-ring sealing environments.
Please see our O-ring groove design tables for more specific recommendations, or get in touch with our engineering team.
