The function of a scraper ring is to prevent dirt particles from entering the components in a hydraulic or pneumatic circuit; cylinders or valves. This helps prevent contamination of the media which will damage the seal, the surface of the housing and the guide bush.

Bellows provide a complete protection for reciprocating shafts, but they are complicated to produce and can be easily damaged so their use is restricted to special applications. In most cases a scraper ring having one-lip made of wear resistant elastomer, is sufficient.It is important to protect the scraping edge from damage and to have adequate contact with the groove and piston rod diameter.

The lip of the scraper ring is designed to have a pre-load with the piston rod, and this has an influence on the break-out friction. Together the pre-load and the sharp scraper edge wipes off the oil film passing the seal.

Scraper rings are made from elastomeric or thermoplastic materials and some have metal case for stiffness. Special designs are available for applications where, compensation for large radial movements or a stiffer inner lip is required.It is recommended to use scraper rings which are designed to be a tight fit in the housing.

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