Primary Lip + Auxiliary Dust Lip
Double lip oil seals combine a primary sealing lip (with garter spring) and an auxiliary dust lip on the outboard side. The dust lip excludes dirt, water, and contamination from contacting the primary seal - extending service life in industrial environments where exposure to dust, debris, or moisture is unavoidable.
What Is a Double Lip Oil Seal?
A double lip oil seal has two contacting lips: a primary lip (oil-side) that retains lubricant and is supported by a garter spring, plus an auxiliary lip (air-side) that excludes dust and contaminants. The space between the two lips can be packed with grease at installation to create a barrier zone that traps particles before they reach the primary lip.
Most general-purpose industrial oil seals are double lip configuration. The standard Durus TC and TB2 types are double lip - providing dust exclusion that adds meaningful service life over single lip designs in any environment where dust contact is possible.
When to Choose Double Lip
- Outdoor equipment - Conveyors, agricultural machinery, construction equipment exposed to airborne dust and debris
- Dirty industrial environments - Steel mills, cement plants, mining operations with high particulate contamination
- Water spray exposure - Washdown environments in food processing, vehicle service, or marine applications
- End-of-shaft positions - Output shafts protruding into the operating environment (vs interior shafts in sealed housings)
- Long service intervals - Applications where rapid seal change-out is impractical; the dust lip extends life
Common Double Lip Seal Types
| Type Code | Construction | Best For |
|---|---|---|
| TC | Type C case (full rubber coat) + Standard double lip | Most common - general-purpose industrial sealing |
| TB2 | Type B case (bare metal) + Standard double lip | Hard housings, double lip with bare-metal OD |
| SB2 | Type B case + S-style with auxiliary lip | Metal-case construction with dust exclusion |
Double Lip vs Single Lip Selection
When in doubt, choose double lip. The marginal cost premium over single lip is small, while the dust exclusion provides meaningful service life extension in any application with potential contamination. Reserve single lip for specifically clean applications or where friction reduction is a design priority.
Browse single lip oil seals for clean environments, or browse all Durus oil seals for the complete catalog.
Related Categories
Frequently Asked Questions
What is the purpose of the dust lip on a double lip oil seal?
The auxiliary dust lip excludes airborne dirt, dust, water, and other contaminants from reaching the primary sealing lip. Particles that contact the primary lip directly cause abrasion, scoring, and premature wear of both the lip and the shaft. The dust lip creates a protective outer barrier, optionally with grease packed between the two lips for additional contaminant trapping. This significantly extends seal service life in any environment where contamination is possible.
Should I always choose double lip over single lip?
For most industrial applications, yes. Double lip seals provide meaningful service life extension in any environment with potential dust, dirt, or water exposure - which describes the majority of industrial applications. The marginal cost increase over single lip is small. Reserve single lip configurations for specifically clean applications (interior gearbox positions where the outboard side is already protected) or where friction minimization is a design priority (high-speed shafts).
What is the difference between TC and TB2 double lip seals?
Both are double lip configurations with a primary lip and auxiliary dust lip. The difference is the case construction. TC has a full rubber outer coating that provides better OD sealing, accommodates housing tolerance variations, and prevents damage to softer housing materials during installation. TB2 has a bare metal outer case (with a lead-in chamfer for easier install) - preferred for hard housings where the rubber coat would be unnecessary. TC is the more common choice for general industrial use.
Can I pack grease between the lips of a double lip seal?
Yes - and it is recommended for dirty environments. At installation, pack the cavity between the primary lip and dust lip approximately 30-50% full with a high-quality grease compatible with the operating temperature and any potential fluid exposure. The grease traps fine particulates that bypass the dust lip and lubricates the area between lips, reducing friction. Refresh the grease at seal change intervals or whenever the equipment is opened for service.
Cross-reference from any CR, SKF, National, Federal-Mogul, or Timken part number. Houston, TX warehouse stocks the full Durus catalog with same-day shipping for in-stock items.
Call (888) 203-2358 or email sales@texasbelting.com with your existing part number, equipment make/model, or shaft and bore measurements.
