Machinery Lubrication

Machinery Lubrication March April 2017

Machinery Lubrication magazine published by Noria Corporation

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Page 58 of 88

ydraulic wiper seals are the first line of defense in many hydraulic systems. Unfortu- nately, they are also a perpetual problem for most users of hydraulic machinery. Microscopic scratches and gouges on the surface of cylinder rods can significantly reduce the life of wiper seals and give contaminants an easy path into the system. Particles as small as 5 microns can act like sandpaper on these surfaces, causing a chain of wear that grows exponentially in these fine-tolerance systems. Wiper seals, which are also known as scrapers, excluders or dust seals, are installed on the external side of the cylinder head to prevent dirt, dust, chips and mois- ture from entering the cylinder/piston rods as they retract into the system. This in turn prevents contamination of the hydraulic oil, which could damage wear rings, seals and other sensitive components. Wiper Seal Designs Wiper seals are not created equal, nor should they be, as they must work in many diverse industries. They must also deal with contamination from high-pressure wash- downs, exposure to extreme weather and chemical attacks. To survive these condi- tions, wiper seals are typically made from heavy-duty materials like high-performance polyurethane. In addition, there is the design factor to consider, including the seal's lip and groove geometry. When the cylinder rod extends past the rod seal, a thin film of oil remains on the rod, trapped in microscopic surface imper- fections. The thickness of the oil film will depend on the surface finish, rod seal and surface speed of the rod. During the return stroke, this thin film can be removed by an aggressive wiper lip, resulting in system leakage. Therefore, it is important to prop- erly pair wiper and rod seals. For example, an aggressive wiper lip design requires an aggressive rod seal lip design. If the wiper and rod seals are not matched correctly, leakage and premature failure can occur. Some of the more common wiper seal designs include single lip, straight lip, beveled lip, rounded lip and double or HYDRAULIC H MITIGATE H y d r a u l i c s How to Contaminant Ingression Systems 54 | March - April 2017 | BACK PAGE BASICS mich a el BroW n | Nori a Corpor at ioN Wiper seal with single lip Straight wiper lip Beveled wiper lip Rounded wiper lip Wiper with double or redundant seal lips Internal Wiper Lip External Wiper Lip in

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