Pneumatic Wiper Seals

Pneumatic wiper seals are located in the cylinder head gland of a pneumatic cylinder, acting as the outermost seal. Their vital function is to scrape dirt, dust, water, and other environmental contaminants from the piston rod as it retracts into the system. This prevents foreign particles from entering the cylinder and damaging the internal components and primary rod seal.
Function and Design
Wiper seals play a critical protective role in maintaining the health and extending the lifespan of the entire pneumatic system.
Contamination Exclusion: They are the first line of defense, creating a physical barrier to stop environmental debris from reaching the sensitive interior of the cylinder.
System Protection: By blocking contaminants, the wiper seal protects the piston rod's polished surface and the primary rod seal from wear, abrasion, and potential failure.
Lubrication Management: In lubricated air systems, the wiper seal helps clean excess oil from the rod on the out-stroke while ensuring enough is left for proper seal lubrication. In lube-free systems, the self-lubricating properties of the seal material are essential for dry running.
Low Friction Requirements: Like all pneumatic seals, wipers are designed with low friction characteristics to ensure smooth operation, high speed capability, and minimal stiction in the system.
Materials
Material selection is key to the wiper seal's effectiveness and longevity, considering exposure to the environment and the need for low friction.
Polyurethane (PU): The most common and versatile material, known for excellent abrasion and wear resistance, high tensile strength, and toughness.
Nitrile Rubber (NBR): A general-purpose elastomer used in standard, lubricated systems, offering cost-effective performance.
PTFE (Polytetrafluoroethylene): Offers very low friction, high chemical resistance, and wide temperature tolerance, making it suitable for high-speed or lube-free applications.
Fluoroelastomer (FKM/Viton): Used for applications requiring higher heat tolerance or chemical resistance than NBR can provide.
Common Applications
Pneumatic wiper seals are essential for virtually any pneumatic cylinder that operates in an environment exposed to external elements.
Factory Automation: Essential for equipment used in assembly lines, sorting, and packaging where ambient dust or debris may be present.
Automotive Manufacturing: Protects cylinders on robotic arms and welding equipment in challenging industrial environments.
Wood Processing Machinery: Shields systems from sawdust and wood chips prevalent in the industry.
Medical Equipment: Found in various devices where maintaining cleanliness and preventing the ingress of dust or fluids is important.
Food Processing: Used in machinery where hygiene is critical, preventing contaminants from entering the system.