Each seal (or gasket) can be classified into one of two types with regard to the motion acting relatively upon it. Static Seals When there is very little or no motion of the mating assembly parts upon the seal, a static condition exists. Usually just an initial compression or periodic (open and close) compressions typify this type of seal; i.e. a liquid seal in a hose joint, a door seal on a home. Design Considerations are rather straightforward. - When compressed, as with an O-ring or face gasket, pressure acts in essentially a vertical direction relative to the face, squeezing between two opposing surfaces to eliminate gaps. - Outward expansion results in the horizontal direction as a pressure relief, and this profile change needs to be accommodated in the mounting surface design. - Compression forces need to be assessed. Various design elements can be introduced if too high; i.e., lower durometer, hollow shapes, sponge/foam and/or thin walls. - Recommended compression range is 10% - 30%, and no more than 50%.