Oil seals can be classified according to their structure, material, sealing principle, and application scenarios. Below are the common types and their characteristics:
1. By Structure
Lip-type seals
Single-lip seal: The most basic type, with only one sealing lip, used for dust prevention or low-speed, low-pressure environments.
Double-lip seal: The main lip prevents medium leakage, while the secondary lip blocks dust intrusion, suitable for dusty environments.
Multi-lip seal: Designed with multiple lips for special media or multi-layer protection.
Spring-reinforced oil seal The sealing lip contains a spiral spring that provides continuous tightening force, compensating for shaft eccentricity or wear. This is the most widely used type.
Metal-cased oil seal Embedded metal casing enhances structural strength, suitable for high-pressure and high-temperature conditions.
Exposed frame / Encased frame
Exposed frame: Metal surface is visible, requiring corrosion protection during installation.
Encased frame: Metal casing is fully covered with rubber, offering corrosion resistance and easier installation.
Hydrodynamic oil seal The lip is designed with return grooves (such as
spiral or wave patterns). During rotation, a pumping effect returns leaked oil
to the sealing chamber, improving sealing performance.
2. By Sealing Material
Nitrile rubber (NBR): Oil-resistant, general-purpose, operating temperature range -40℃ to 125℃.
Fluorocarbon rubber (FKM): High-temperature and corrosion resistance, operating range -20℃ to 250℃.
Silicone rubber (VMQ): Excellent low and high temperature resistance, but lower wear resistance, operating range -60℃ to 225℃.
Polytetrafluoroethylene (PTFE): Chemical resistance and low friction, suitable for harsh environments.
Polyurethane (PU): High wear resistance and pressure resistance, commonly used in construction machinery.
3. By Working Conditions
Rotary shaft oil seal: Used for rotating shafts such as engine crankshafts and gearbox shafts.
Reciprocating oil seal: Applied in hydraulic cylinders and piston rods, commonly in U-shaped or Y-shaped seals.
Static seal: Used in static components such as flanges and end covers, typically O-rings or gaskets.
4. Special Types
Labyrinth seal: Non-contact type, prevents leakage through a tortuous gap, suitable for high-speed rotating equipment.
Combination seal: Integrates multiple sealing functions.
5. Selection Considerations
Type of medium: oil, water, chemical solvents, etc.
Operating temperature: within the material’s tolerance range.
Pressure and speed: high-speed and high-pressure require special designs.
Shaft surface roughness and eccentricity: directly affect seal life.
Environmental factors: dust, humidity, corrosive conditions.
Oil seals come in many types, and selection should consider operating conditions, medium, and cost. Lip-type seals are the most common, while PTFE or FKM materials are recommended for special environments. Proper installation and maintenance are critical to extending service life.
