Wiper Hydraulic Seals

Wiper hydraulic seals, also known as scrapers or excluders, are crucial components in a hydraulic system positioned as the outermost seal in the cylinder head. Their primary function is to scrape dirt, dust, moisture, and other external contaminants from the surface of the piston rod as it retracts into the cylinder, preventing damage to the rod and internal components.
Function and Design
Wiper seals play a vital protective role in maintaining the integrity and extending the life of the entire hydraulic system.
Contamination Exclusion: They act as a physical barrier against environmental debris, stopping contaminants from entering the hydraulic fluid and cylinder assembly.
System Protection: By preventing the ingress of abrasive particles, the wiper seal protects the more sensitive rod seal, piston seal, and the highly polished surfaces of the cylinder bore and rod from wear and damage.
Film Management: While the rod seal is designed to leave a minimal lubricating film on the rod during retraction, the wiper seal is intended to clean this film off on the next stroke to prevent external leakage and mess, while still allowing enough lubrication for its own operation.
Rod Guidance: Some designs can also offer a certain level of guidance to the rod, contributing to overall system stability.
Types of Wiper Seals
Wiper seals come in various profiles to suit different operating environments and gland designs.
Single-Lip Wipers: These have a simple design, primarily focused on scraping debris from the rod.
Double-Lip Wipers: These feature an additional, secondary lip on the inside that provides a light sealing action, offering a backup to the primary rod seal and further enhancing contamination control.
Metal-Cased Wipers: The elastomer element is bonded to a metal outer shell, providing a secure, rigid fit in the gland and making installation easier.
Snap-in Wipers: These are often made entirely of a resilient polymer like polyurethane and can be easily snapped into an open-faced gland.
Materials
Material selection is key to the wiper seal's effectiveness and longevity, as it must withstand environmental exposure and abrasion.
Polyurethane (PU): The most common material due to its excellent abrasion and wear resistance, high tensile strength, and general resilience. It handles impacts and minor misalignments well.
Nitrile Rubber (NBR): A general-purpose material with good resistance to petroleum-based hydraulic oils and a wide operating temperature range.
Fluoroelastomer (FKM/Viton): Used for applications involving higher temperatures or exposure to a broader range of aggressive chemicals and synthetic fluids.
PTFE (Polytetrafluoroethylene): Offers very low friction, high chemical resistance, and wide temperature tolerance, particularly useful in extreme environments.
Common Applications
Wiper seals are essential for almost any hydraulic cylinder that operates in an environment exposed to external elements.
Construction Equipment: Vital for excavators, loaders, and cranes that operate in dirty, muddy, and dusty conditions.
Agricultural Machinery: Protects cylinders on tractors, harvesters, and other farm equipment from soil and crop residue.
Mining and Heavy Industry: Essential for heavy-duty machinery exposed to harsh, abrasive materials and moisture.
Waste Management: The robust design handles the challenging conditions in refuse collection and processing equipment.
Forklifts and Material Handling: Ensures reliable operation of lifting mechanisms in warehouses and industrial settings.