PADV wiper seals
PAD seals are press-in wiper seals and feature a double-lip design with an internal wiping lip that regulates the lubricating film on the rod. On the extension stroke, the inner lip wipes excess fluid film from the rod and allows this excess fluid to return beneath the rod seal on the return stroke. Double-acting wipers therefore improve performance and extend the service life of rod sealing systems.
However, excessive system pressure acting on the inward-facing lip, for example fluid passing a damaged rod seal, could overcome the press-fit force between the housing and steel retaining ring and push the wiper seal out of the housing. SKF therefore recommends using double-acting wiper seals in combination with single-lip rod seal U-cups, such as the S1S profile, to ensure that pressurised fluid returns to the hydraulic system. Where the housing is pressurised, the wiper seal can also be positively retained in the housing.
PAD profiles are also available with a vent in the inner lip (designation PADV). In most applications they do not require additional retaining rings. The vent prevents pressure build-up at the inner lip. PAD and PADV profiles are available in the same metric sizes.