Exclusion Seals

Exclusion seals, wipers, and scrapers clean the surface of a retracting rod, removing abrasive particles such as dirt, mud, and ice. This protects the seal and extends service life. The importance of wipers cannot be overemphasized. Often a seal fails prematurely because the wiper wears out long before the primary seal. In such cases failure is not due to misapplication of the seal, but to the wiper not protecting the seal from abrasive wear. are usually produced from a material like high-quality polyurethane. They are designed to snap directly into the glands on common cylinders. Typical properties for wiper materials are: hardness, 85-95 Shore A; tensile strength, 6,000 psi; elongation, 400%. They can typically be used in a temperature range from -40 to 210°F, although some manufacturers predict reduced life if the rods are exposed to steam and water over 190°F. are made with a sealing lip at the bottom and a rod wiper at the top, so the wiper can perform as a pressure-energized lip seal inside the cylinder at the same time it wipes contaminants from the outside. The two most common types are a double-lip U-seal and a double-lip V-seal. Both are one-piece snap-in replacement seals that provide both sealing and wiping action. are exclusion seals that have a metallic lip or hard plastic scraping element to scrape heavy or tenacious materials from reciprocating shafts. The hard lip is kept sharpened by the honing action of the shaft. Wipers are sometimes used behind scrapers to catch any fine particles or fluids that pass the scraper. There are two types of scrapers, conical scrapers and scraper rings. The conical scraper has a sharp knife edge that digs under the foreign matter and lifts it from the shaft. The scraper ring has a flat top, 1/32 to 1/16 in. wide.