What is the difference between rod seals and piston seals?

 A rod seal sits in the cylinder head (gland) and seals around the moving piston rod, keeping hydraulic oil from leaking out of the cylinder. A piston seal sits on the piston and seals between the piston and the cylinder bore, keeping pressure separated between the two chambers. In short, rod seals prevent external leakage, while piston seals prevent internal leakage (bypass). Both are dynamic seals, but they work on different surfaces, handle different loads, and fail in different ways. Every hydraulic cylinder depends on a set of seals working together. The rod seal and piston seal are often confused because both hold pressure against a sliding surface. Knowing what each one does, where it sits, and how it fails makes it easier to select the right seal, diagnose leaks, and plan maintenance.

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