Seals play an important role in hydraulic cylinders—they contain the fluid and prevent the leakage of fluid between components. They fall into two main categories: dynamic and static. Dynamic seals are used in between parts that are in relative motion. The seals for a rod sealing system protect the dynamic reciprocating motion for the piston rod and head. The dynamic reciprocating motion between the piston and cylinder bore is another area of a hydraulic cylinder that uses dynamic seals.