Spring-Loaded Rotary Seals

Spring-loaded rotary seals use a mechanical spring, typically a garter spring, to apply a consistent radial force to the sealing lip, ensuring continuous contact with the shaft surface. This mechanism is crucial for reliable sealing, particularly in demanding applications involving high speeds, fluctuating pressures, and aggressive media, or where the seal material has limited elasticity.
Design and Function
The primary function of the spring is to compensate for factors that would otherwise compromise the seal's integrity.
Consistent Pressure: The spring maintains uniform pressure on the seal lip against the rotating shaft, even as the lip wears down over time.
Compensation: It accommodates minor shaft runout, misalignment, and dimensional changes due to thermal expansion or contraction.
Reliability: This mechanism provides a highly reliable, virtually leak-free seal in both dynamic and static conditions, even at low pressures before system pressure is applied.
Types of Springs
Different spring designs are utilized depending on the application requirements, such as friction sensitivity or temperature range.
Garter Springs: These are coiled springs connected at both ends to form a circle and are the most common type used in radial shaft seals. They ensure a constant force on the shaft and are good for high runout conditions.
Canted Coil Springs: Made from round wire formed into a slanted shape, these offer a very flat load versus deflection curve. This makes them ideal for applications that are sensitive to friction or have wide gland tolerances.
Helical-Wound Springs: Constructed from a flat metal strip, they provide a high progressive load and are suitable for low-temperature (cryogenic) and vacuum applications, though they have a small deflection range.
Cantilever (V) Springs: These metal strips concentrate the load at the front of the seal, making them a good choice for scraper or excluder functions in reciprocating applications, and can handle wide tolerances.
Materials
The seal jacket material, often combined with various fillers, is selected based on chemical compatibility and operating conditions.
PTFE (Polytetrafluoroethylene): The most common material for the seal jacket due to its near-universal chemical resistance, extremely wide temperature tolerance (from cryogenic to over 260°C), and very low coefficient of friction. Fillers like graphite, carbon, or bronze can enhance wear resistance and strength.
Nitrile Rubber (NBR): Used in more standard, general-purpose applications with mineral oils and greases.
Fluoroelastomer (FKM/Viton): Provides excellent resistance to high temperatures and a broad range of aggressive chemicals.
High-Performance Polymers: PEEK, polyethylenes, and polyimides are also used in extreme temperature or abrasive environments.
Common Applications
Spring-loaded rotary seals are employed across diverse industries, particularly in critical applications and harsh environments.
Automotive: Used in engines (crankshafts, camshafts), gearboxes, and wheel hubs to retain lubricants and exclude contaminants.
Aerospace: Employed in turbines, actuators, and cooling systems due to their ability to withstand extreme temperatures and pressures.
Oil & Gas: Critical for pumps, valves, and compressors to prevent leakage of aggressive or hazardous fluids.
Heavy Industry & Mining: The robust design and ability to exclude contaminants make them ideal for machinery operating in dirty, demanding conditions.
Food and Pharmaceutical: Specific materials (e.g., FDA-compliant PTFE) are used to meet strict hygiene standards and resist harsh cleaning agents.