Wipers are parts that prevent dirt from entering the cylinder. They are designed to remove or scrape off dirt deposited on the shaft, but must allow a light film of lubricant to be present when the shaft is returned.
The ingress of dirt particles into the cylinder would lead to contamination of the lubricant and damage to other sealing and guiding elements of the cylinder itself.
Flexible and rigid designs are available, as well as dual function wipers which combine their own seal with a secondary seal for the piston rod. Low friction wipers combine a PTFE profile with fillers and an elastomer seal (usually NBR) to give the PTFE ring the required elasticity.
Constructions in nitrile (NBR), polyurethane (AU) or filled PTFE.