Single Lip Rotary Seals

Single lip rotary seals are mechanical components designed primarily to retain lubricants and prevent fluid leakage in rotating shaft applications, typically where external contamination is low. They feature a single sealing lip, often energized by a spring, which maintains contact with the rotating shaft.
Design and Function
The core function of a single lip seal is to create a dynamic seal between a rotating shaft and a stationary housing.
Sealing Lip: The flexible lip creates a barrier by maintaining continuous contact with the shaft surface.
Garter Spring: Many designs include a garter spring that applies a constant radial force to the lip, ensuring consistent contact and compensating for minor shaft variations or runout.
Outer Casing: A metal or rubber-covered outer diameter provides structural integrity and a secure static fit within the housing bore.
Functionality: Unlike double-lip seals which have an additional secondary lip for dust exclusion, single-lip seals focus solely on sealing internal media. This design results in lower friction, less energy consumption, and reduced heat generation.
Materials
The material selection depends on the operating conditions, including temperature, pressure, chemical exposure, and shaft speed.
Nitrile Rubber (NBR): A common general-purpose material known for good resistance to mineral oils, greases, and normal fuels.
Fluoroelastomer (FKM/Viton): Offers excellent resistance to high temperatures and a wide range of chemicals.
Polytetrafluoroethylene (PTFE): A high-performance material used for extreme conditions, offering very low friction, high chemical resistance, and the ability to run dry.
Supporting Rings/Cases: Typically made from low-carbon steel, stainless steel, or aluminum alloys for rigidity.
Common Applications
Single lip seals are widely used across various industries where the primary goal is fluid retention and the external environment is relatively clean.
Automotive Systems: Used in some engines for sealing the crankshaft or camshaft.
Electric Motors: Prevent lubricant leakage in small electric motors.
Pumps and Gearboxes: Ensure oil or grease containment in industrial machinery.
Compressors: Provide reliable sealing in industrial compressors, with potential for long service life.
Food and Pharmaceutical Equipment: Specific materials (e.g., FDA compliant PTFE) are used to maintain hygiene standards.
Aerospace: Employed in systems like APUs and gearboxes where they can withstand extreme conditions.
Key Considerations
When selecting a single lip rotary seal, key factors include:
Shaft Surface Finish: A smooth surface is preferred for optimal seal performance and longevity; however, excessive smoothness can hinder lubrication.
Shaft Hardness: The seal material should be softer than the shaft to prevent shaft wear, which can be costly to repair.
Operating Conditions: Pressure, temperature, and rotational speed must be within the seal's specified limits for effective operation.