What Do O-rings Do?
An o-rings primary use is for sealing. They are designed to be seated in a groove and compressed during assembly between two or more parts, creating a seal at the interface. O-rings are often used in static (non-moving) applications but are also found in dynamic (moving) applications where there is relative motion between the parts and the o-ring itself.
Dynamic (moving) use examples include: rotating pump shafts and hydraulic cylinder pistons.
Examples of static (non-moving) include: fluid or gas sealing applications in which the o-ring is compressed, resulting in zero clearance.
Some o-rings are made with lobed (x-like) cross-sections to work in both static and dynamic applications.
There are around 20 different types of o-rings available to cover these multiple uses. The common round cross-section is the most versatile. This conventional o-ring can be used in almost any application as long as the gland to contain the o-ring is designed correctly and correct size and material are chosen.
Silicone O'rings / SIL
Silicone rubber is used in high and low temperature applications. Silicone can be FDA approved and come in Military Specifications as well as several other common classifications. Silicone rubber is usually non-reactive and stable in most environments. It is used in many different applications for its versatility. Silicone comes in many colors though it is frequently white or opaque.