Hydraulic cylinders operate in a variety of applications and environmental conditions, including exposure to dust, debris or outside weather conditions. To prevent these contaminants from entering the cylinder assembly and hydraulic system, dust seals (also known as scrapers, excluders or wiper seals) are fitted on the external side of the cylinder head (fig. 1).

　　Dust seals maintain sealing contact to the piston rod when the equipment is stationary (static, no reciprocating motion of rod) and in use (dynamic, reciprocating rod), whereas the tolerance for the rod diameter d is determined by the rod seal. Without a dust seal, the retracting piston rod could transport contaminants into the cylinder.

　　The outside static sealing of the dust seal within the housing is also important to avoid moisture or particles from entering around the outside of the wiper seal.