These dynamic-working sealing elements are mostly used in pneumatic and hydraulic systems. There is a metallic ring inside of the seal as well as elastomeric material. That additional metal part gives some advantages on hardness, strength and mechanic abilities. Pneumatic seals can be produced with springs for medias that have low pressure hydraulic. This spring adds an additional radial strength to lips of the seal..
Pneumatic seals can provide the sealing on both sides.