Overview of Seal Design Section

The purpose of the Seal Design section is to assist in designing a groove for a specific size o-ring, to search for possible standard o-rings for an existing groove or to evaluate an o-ring in an existing groove. The results of this section will require some analysis by the user. Ideally, the Seal Design section is used after a product has been selected for the application. The following describes the functionality of the Seal Design menu options.

Design a Groove for a Specific Size O-Ring

This section of the program is used to design a groove type for a specific size o-ring

1. As a first step, the process conditions and design parameters need to be entered. Chemical swell is estimated if actual performance data is unavailable. The table below provides a rough estimate of the chemical swell of a Kalrez® product. The rating color for Kalrez® products can be obtained from the Kalrez® Product Selection section of the Guide.
   
   How to match a rating color from the Kalrez® Product Selection section with a chemical swell value.

   Green - 3% volume swell
   Blue - 15% volume swell
   Yellow - 30% volume swell
   Red - Product is not recommended for the application

2. Installed Compression is the initial compression on the o-ring, in the groove, at room temperature. Values for compression vary depending on the type of seal; dynamic, static, vacuum, etc. The data below provides some typical nominal compression values. The program defaults to these values

   Seal Type	Nominal Compression
   Dynamic	8%
   Static	16%
   High pressure gradient (vacuum) seals	20%

3. The Free Volume is the amount of empty groove space that is targeted at the operating conditions. A typical value for free volume is 16%, and is used for most grooves. This leaves sufficient room for additional o-ring expansion in the case of higher operating temperatures, higher than anticipated o-ring swell due to the chemical environment, etc.

It is suggested that the design utilize nominal o-ring dimensions. A standard o-ring can be used or specific o-ring dimensions can be entered. Tolerances can be applied to the groove and these will be used in the groove dimension calculation. O-ring Performance values are calculated for the groove and o-ring combination that were chosen.

O-ring Options for a Nominal Groove

This section of Seal Design determines if any standard o-rings are available for an existing groove.

1. The groove dimensions must be entered in the program. It is suggested that as much information as possible be input about an existing groove. That would include the nominal dimensions as well as dimensional tolerances. Groove information is then entered directly into the Dimensions table or can be entered directly into a diagram by clicking on the Edit Via Diagram button.
2. Search settings must be input to define the operating conditions. These include such values as Temperature, estimated Chemical Swell, Minimum and Maximum values for various groove configurations, Minimum and Maximum CSD (cross section diameter) Compression for the o-ring (as installed), etc. Enter the Minimum Free Volume allowed in the groove at operating conditions.
3. The following are suggested minimum and maximum compression values for o-ring search criteria.

   Seal Type	Minimum CSD Compression	Maximum CSD Compression
   Dynamic	6%	10%
   Static	14%	18%
   High pressure gradient	18%	22%

4. For Minimum Stretch and Maximum Stretch, the value range chosen depends on the type of seal and whether the pressure is internal or external. For example, if the o-ring needs to be stretched, then it may be stretched typically 0.5% to 3%. If an o-ring is stretched beyond 5%, the additional stress may lead to premature failure. Suggested search criteria are listed below. These are suggested guidelines only and individual applications may require different criteria.

   Groove Type	Minimum Stretch	Maximum Stretch
   Flange Seal With External Pressure	0%	5%
   Crush Seal With Chamfer in Housing	-2%	5%
   Dovetail Groove	-2%	5%
   Dovetail Groove – Sidewall Height (ID<OD)	-2%	5%
   Half Dovetail Groove	-2%	5%
   Reverse Half Dovetail Groove	0%	5%
   Piston/Housing With Groove in Piston	0%	5%
   Piston/Housing With Groove in Housing	-1%	5%

   When a seal is used with internal pressure or a chamfer on plug, then the o-ring should be situated toward the outer edge of the groove. In the two groove types below, OD interference refers to compression on the outer diameter of the o-ring from the outer diameter of the groove.

   Groove Type	Minimum OD Interference	Maximum OD Interference
   Flange Seal With Internal Pressure	-5%	1%
   Crush Groove With Chamfer on Plug	-5%	1%

5. The final information needed for a search is the Minimum Free Volume. This is the minimum amount of free volume acceptable for the groove at operating temperatures. A typical search value is 5%, although this could be changed depending on the application information.

The program displays any o-ring sizes that fit the search criteria and the o-ring performance values when used in the service. This information can be reviewed to determine which o-rings best fit the service.

Design a Custom O-ring for a Nominal Groove

This section of the Seal Design is used when a standard size o-ring does not properly fit in an existing groove. Although a custom ring will have to be designed and molded, this method often yields the optimum o-ring/groove combination. A nominal compression value is requested since the o-ring is designed for a specific groove and optimum conditions can be chosen. When all conditions are entered the program will automatically calculate the custom o-ring dimensions. Nevertheless, a custom o-ring may still not be suitable for the groove.

Evaluate an O-Ring for Use in an Existing Groove

This section is most useful for determining if an o-ring is properly sized for a groove. This may be especially important if there has been an o-ring seal failure. If not already entered, groove dimensions can be entered directly into the dimension table or into a diagram of the groove by clicking on the Edit Via Diagram button. After entering the groove dimensions, enter the application parameters as well as the o-ring size or dimensions. Changes can then be made interactively to evaluate the effect of these changes on the groove/o-ring fit.

The O-ring Performance Values include initial and operating o-ring compression, initial ID stretch (or OD interference) and the free volume in the groove. These values will change depending on the type of groove and specific application. Typical values have already been listed in previous sections of this detailed program overview. The typical values are only a guideline and many o-ring applications will perform satisfactorily even if the values are outside of the suggested ranges. However, the further outside the range, the more susceptible the o-ring is to premature failure.