Double Lip Rotary Seals

Double lip rotary seals have two sealing edges: a primary inner lip to retain lubricant and a secondary outer lip to prevent the ingress of external contaminants like dust, dirt, and moisture. This design offers enhanced protection for machinery in harsh environments compared to single lip seals.
Design and Function
The dual-lip design provides a robust sealing solution for demanding applications.
Primary Lip: This inner lip is the main seal, designed to press against the rotating shaft to contain oil, grease, or other fluids within the system. It is often spring-loaded with a garter spring to ensure consistent pressure and reliable sealing.
Secondary (Auxiliary) Lip: Positioned on the outside of the primary lip, this extra edge acts as a dust wiper or barrier, actively blocking the intrusion of external contaminants.
Enhanced Protection: The combination of lips ensures that the internal components are safeguarded from both fluid leakage and environmental debris, leading to a longer service life for the equipment.
Materials
Double lip seals are available in various materials to suit specific operating conditions and fluid compatibilities.
Nitrile Rubber (NBR): A common and versatile material with good resistance to mineral oils and greases. It can tolerate temperatures typically up to 100°C (212°F).
Fluoroelastomer (FKM/Viton): Provides excellent resistance to high temperatures and a broader range of aggressive chemicals and fuels, suitable for more extreme conditions.
Polytetrafluoroethylene (PTFE): Used in high-performance applications with very low friction, high chemical resistance, and the ability to run at high speeds and temperatures (up to 260°C or 500°F), often requiring a harder shaft finish.
Metal Casing: The outer casing, which provides a static seal and structural integrity, is typically made of steel or stainless steel, especially for applications requiring corrosion resistance.
Common Applications
Due to their superior contamination resistance, double lip seals are favored in harsh environments.
Heavy-Duty Machinery: Widely used in construction and agricultural equipment (e.g., excavators, bulldozers, tractors) that operate in dirty and dusty conditions.
Automotive Systems: Employed in wheel hubs, transmissions, and axles to protect bearings from dirt and water ingress.
Industrial Gearboxes and Pumps: Ensure reliable containment and protection in demanding industrial settings.
Marine Applications: The secondary lip is particularly effective in wet environments, protecting shafts and bearings from water ingress in boats and ships.
Performance Considerations
While offering enhanced protection, double lip seals have some performance differences compared to single lip seals:
Increased Friction: The presence of two lips in contact with the shaft results in higher friction and consequently increased heat generation and energy consumption.
Speed Limitations: The higher friction can limit their use in very high-speed applications where the secondary lip might overheat from lack of lubrication.
Cost: They are generally more expensive to produce and purchase due to their more complex design and additional material.