Generally, hydraulic type seals are considered to be non-metallic, soft rings that are fixed within combination of rings thus creating a seal assembly shape. They may also be captured in groves. Their function is to separate or block fluid in different reciprocating motion applications. These seals do play a crucial role in machinery. They offer fluid power that gets converted into linear motion. https://bmgworld.blogspot.com/2022/06/know-different-types-of-hydraulic-seals.html