Seal Design ยป O-Ring Technical Resources

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The o-ring seal design process begins with understanding the gland type in which the seal will be seated. To ensure the o-ring fits properly it is recommended that the o-ring is stretched 1 to 5% circumferential, with ideal stretch at 2%. Further considerations listed below include; seal gland type, sealing application (fluid, solid gas), pressures, operating temperatures, and chemical interactions.


Each factor involved with the o-ring seal selection should be weighed with the elastomers capabilities and tested thoroughly to ensure the seal design meets the applications demands.

O-Ring Seal Design Links
General Seal Design Factors
O-ring seal gland types

General Seal Design Applications

Materials Links

Gland Design Information

Seal Design Consdierations
Basic O-Ring Design
Basic O-Ring Design
Oring Types of Squeeze
Oring Basci Applciations
Basic Applications
OPring Cross Section / Inside Diameter Calculations
Oring Troubleshooting
Link: Dynamic Radial Gland Design
Link: Dynmaic Reciprocating Glands
Link: Dynamic Rotary Glands
Link: Dovetail Glands
Link: Static Radial Gland Design
Link: Static Axial Interal Pressure Glands
Link: Static Axial External Pressure Glands
Link: Static Crush Gland Design
Link: Oring Materials
Materials / Elastomers
Link: Orings By Materials

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Link: Rubber Material Design
Link: ASTM Classification
Link: Oring Factors Affecting Tolerances

Quick Links

Link: Gland Design Home Page
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O-Ring Seal Design

Preliminary O-ring Design Considerations
An o-ring is a simple and versatile ring shaped packing or sealing device. Having a circular cross section that functions as a seal, in both static and dynamic applications, by being compressed between the mating surfaces comprising the walls of the gland, in which it is installed. Although o-rings can be made from a variety of materials, they are most commonly molded in one piece from an elastomeric material.
 
1. What will be the function of the part 2. What type of Environment will the product be subjected to
- Seal a fluid - Any water, chemicals, or solvents that could cause deformation to the part
- Transmit a fluid - Oxygen or Ozone
- Transmit Energy - Sunlight
- Absorb Energy - Wet or Dry Environment
- Provide Structural Support - Continuous or cycled pressure
  - Dynamic or Static stress
   
3. What is the desired product life 4. What are the desired properties
- Elongation Strength - Compression Set Resistance
- Resistance to Deformation - Resilience (Rebound)
- Compression Sets - Tear Strength
- Resistance to Embrittlement - Heat Aging Resistance
  - Etc. (see materials for more properties)

Basic O-ring Design
How O-rings Seal
An o-ring acts as a seal by blocking any potential leaching path, of a liquid or gas, between two closely matted surfaces. An o-ring is installed in a machined grooved gland (see gland design for examples) in one of the two surfaces to be sealed. As the two surfaces are brought together the o-rings cross section becomes deformed producing a tight seal, see image. The greater the squeeze the greater the deformation . The reason an o-ring acts as such a good seal is because of the elastomer material in which it is made from. An elastomer typically a highly viscous material having the tendency to remember its original shape for a long time, allowing it to be compressed and recompressed without losing its original shape and therefore its sealing ability. It is important to choose the right elastomer for each intended application. Each elastomer has different thresholds for heat, cold water, gas etc. For examples of different elastomers and there unique characteristics please visit Datwyler's elastomer section.
O-ring Seal Design
Types Of Squeeze O-ring Seal Design
As shown, o-ring squeeze may occur in two possible ways.
1. Axial Squeeze "A": Where the squeeze
occurs on both the top and bottom surfaces of
the o-ring.
 
2. Radial Squeeze "B": Where the squeeze
occurs on the inner and outer surfaces of the
o-ring.
 
Basic Applications
Two basic o-ring applications.
 
1. -Static Applications "A": O-ring is contained
within two non-moving parts.
 
2. -Dynamic Applications "B": O-ring is contained
within moving gland walls.
 

Cross Section and Inside Diameter "I.D." Calculation
Dynamic Cross Section   Static Cross Section
- The following refers to a dynamic application, see gland   - The following refers to a static application, see gland design
design section for listings   section for listings
     
1. List the bore diameter   1. List the gland depth and multiply by the minimum and
2. List the piston groove diameter   maximum squeeze requirements ( see the gland design
3. Subtract the groove diameter from the bore diameter,   section for listings).
and divide the difference by two.    
4. Refer to corresponding table (see gland design section   Static I.D. Calculation
for listings) to establish minimum and maximum squeeze   List the diameter of the part that the o-ring that will be
requirements.   stretched over during installation and reduce this figure by 1%
5. Multiply the figure from step three, by the minimum   to 5% therefore reducing the o-rings I.D. to allow for stretch,
and maximum squeeze requirements obtained in step   similar to the dynamic I.D. calculation. Then look up the o-ring
four. The two figures obtained represent the minimum   in the gland design section by I.D. and corresponding
and maximum o-ring cross section diameters, for the   cross section.
particular application.      
    O-ring Seal Design O-ring Seal Design
Dynamic I. D. Calculation  
The inside surface of the o-ring will be resting on the  
bottom of the piston groove. To have a complete seal the  
o-rings I. d. must be smaller than the piston groove diameter  
(see above). The o-rings I. d. therefore will be slightly  
stretched in the application. The stretch should be a minimum  
of 1-2% but not exceeded 5%. The following formula  
calculates the o-ring I. d.  
   
O-Ring I. d. = Groove Diameter / % of stretch desired (1% - 5%)  

 

  
   
       

Reasons for O-ring Failure

 O-rings    
     
Failures are usually due to a number of causes and typically    
include environmental issues. For example, excess friction    
causes heat, which in return causes the o-ring to swell, therefore   Failed O-ring
exposing the o-ring to a possible harsher chemical or environmental  
attack. Successful O-ring  
Such effects may be compounded due to human error in overlooking    
critical elements of gland design; including but not limited to    
preliminary testing, proper o-ring compound use, poor installation,    
lack of proper maintenance or lubrication. Some of the more common Failed O-ring  
reasons for o-ring failure are as follows:  
    Failed O-ring
-incorrect o-ring size   "Non-Fill
-incorrect installation    
-poor maintenance or lack of lubrication    
-incompatibility of the elastomer and the environment subjected too   Failed O-ring
   
These problem causing attributes can be difficult to evaluate, so it is Failed O-ring  
strongly recommended that adequate testing be performed in actual "Extrusion and Nibbling"  
environmental settings.    
     
     
     
      Failed O-ring
      "Breaking or Cracking"
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Due to the number of interacting forces, it is STRONGLY RECOMMENDED THAT YOUR ELASTOMER SELECTION BE RIGOROUSLY TESTED IN THE ACTUAL APPLICATION, performance assumptions must be checked so that you are certain that all variables have been carefully considered
Products Examples by Category
Rubber Molding & Manufacturing:
Engineering, R&D, Product Realization:
Industry Experience & Solutions:
Molded Rubber