Press-in wiper seals
PAD and PADV profiles
PAD profiles (fig. 3) have a double-lip design with an internal-facing wiper lip that regulates the lubrication film on the rod. The internal lip wipes excess fluid film from the rod on extending stroke and allows this excess fluid to return under the rod seal on the retracting stroke. Double-acting wipers, therefore, improve the performance and extend the service life of rod sealing systems.
However, excess system pressure acting on the internal-facing lip, such as fluid passing a damaged rod seal, could overcome the press force between the housing and the steel retaining ring and push the wiper seal out of the housing. Therefore, SKF recommends using double-acting wiper seals in combination with U-cup rod seals with a single-lip design, such as S1S profile, to ensure pressurized fluid can return to the hydraulic system. A snap ring may also be required to retain the wiper seal in the housing (fig. 4) in case of pressure build up.
PAD profiles (fig. 5) are also available with a vent in the internal lip (designation PADV). They do not need extra snap rings in most applications. The vent prevents pressure build-up on the internal-facing lip. PAD and PADV profiles are available in the same metric sizes (→ Size list [pdf]). For additional information, refer to PAD and PADV profile data.