Rod seals are considered the hydraulic seal with the most demanding requirement specifications because they must be the right size, profile and material in order to properly prevent leaks.
Rod seals are made of plastic, rubber or Teflon, depending on the type of fluid to which they are exposed, the amount of pressure and whether the cylinder is single acting, meaning the seals receive dynamic pressure from one side, or double acting, meaning the pressure comes from both sides. They are designed for both linear and reciprocating dynamic sealing applications, and they seal pressure between the inner contact surface of the seal and the outer rod surface while the rod is moving linearly under pressure.
They are used mostly in fluid power equipment applications, including mobile fluid power cylinders, hydraulic cylinders, machine presses and mobile plants within the mining, construction, steel milling, water management and chemical processing industries. They are suitable under low and high pressure, a variety of temperature ranges and are radial and dynamic type of seals.
Rod seals are always press fitted into the housing bore and are contained within moving walls, meaning they must be durable and resistant enough to endure high friction because they are affected greatly by wear and aging as well as changes on the rod surface. They are radial, meaning pressure is applied to both the inner and outer surfaces of the seal.
Rod seals are always round, similar to an o-ring and come in many different shapes and sizes. Their profiles differ considerably, and they may be simple and round, T-shaped, Z-shaped, X-shaped and ribbed, among many other complex profile designs. They fit specifically into the housing bore and their sealing lip always makes contact with the shaft. Rod seals are manufactured three different ways.
They can be extruded and then welded together, which creates a seam, stamped if they have flat profiles or made in a mold. Teflon rod seals must be sintered because Teflon is a material that does not melt. Instead, powder Teflon is heated in a furnace until the powder adheres together and forms a solid product. The seals can be composed of one material or a core material that is coated with a stronger, more resistant substance like Teflon.