Some Rules of Thumb

Following is the first part of our Rules of Thumb series Apple Rubber will be providing in our e-newsletters.

We think you will find a small investment of your time in reading these rules will yield a greater knowledge and understanding of sealing principles. Here are a few to get you started.

1. A stretch greater than 5% on the O-ring I.D. is not recommended because it can lead to a loss of seal compression.
2. A Groove depth is the machined depth into one surface, whereas a Gland depth consist of the groove depth plus diametrical clearance and is used to calculate seal compression.
   
3. To create seal compression the groove depth must be less than the seal cross section. To compensate for this compression, the groove width must be greater than the seal cross section.
4. Static applications are more tolerant of material and design limitations than dynamic applications.
5. The maximum volume of the O-ring should never surpass the minimum volume of the gland.
   
6. For reciprocating seals passing O-rings over ports is not recommended. Nibbling and premature wear and seal failure will result.

Look for more in future issues of this e-newsletter. ALL of these Rules of Thumb and more can be found in the Seal Design Guide section of our web site.