Pillow Block Bearing Seals: Lip vs. Labyrinth Guide

Pillow block bearings are indispensable components in a wide array of industrial equipment, providing robust support for rotating shafts. However, the efficiency of bearings heavily relies on seals.

Seals act as critical barriers. They prevent contamination, retain lubrication, and maintain the operational integrity of the bearing assembly. Bearings seals types vary greatly depending on their intended use.

In this blog post, we'll focus on two main types of pillow block bearing seals --- Lip Seal vs. Labyrinth Seal.

Understanding Lip Seals in Pillow Block Bearings

What Are Lip Seals?

Lip seals are a type of contact seal, specifically engineered for dynamic shaft sealing applications.

Fig 1 Contact Seal

With a notched inner perimeter, these ring-shaped elastomeric components operate by establishing direct frictional contact with the shaft. 

This interaction can keep a thin layer of lubricant between the lip and the shaft. This layer is important for making an effective seal.

They generally feature a metal case and an elastomer sealing lip. Many designs also add a garter spring that ensures consistent contact pressure.

Types of Lip Seals

• SingleLip Seal

Cost-effective, ideal for light-duty applications (such as conveyor idlers).

Fig 2 Single Lip Seal

• Double Lip Seal

The primary lip ensures leak prevention, while the secondary lip provides dust protection (e.g., agricultural bearings).

Fig 3 Double Lip Seal

• Triple lip Seal

Ideal for extreme contamination scenarios (e.g., in mining machinery).

Fig 4 Triple lip Seal

Common Materials of Lip Seals

Lip Seals for pillow block bearings are made of elastomeric materials. They remain reliable even when subjected to significant heat and pressure.

Nitrile (Buna-N):

• Good resistance to petroleum oils, water, fuels, greases, and hydraulic oils.

Temperature range:

• • Continuous: -40°C to 100°C
  • Intermittent: Up to 120°C for <72 hrs  
  • Avoid dynamic use below -20°C

Fluoroelastomer (FKM/Viton):

• better chemical resistance (e.g., gasoline, transmission fluid)
• Suitable for demanding industrial environments

Temp Range:

• Continuous operation: -20°C to +200°C
• Peak: +230°C (Short-term (<24 hrs))
• Low-Temp FKM (e.g., Viton® GLT): -40°C to +200°C
• High-Temp FKM (e.g., Viton® Extreme™): -15°C to +300°C

Ethylene Propylene Diene Monomer (EPDM):

• Outstanding resistance to atmospheric exposure, ozone, and ultraviolet light
• Ideal for outdoor and high-temperature uses

Other Specialized Materials 

• Aflas
• Simiriz
• Polyurethane
• Polyacrylate
• FEP
• carboxylated nitrile
• Fluorosilicone
• HSN
• Silicone
• Neoprene

Advantages of Lip Seals

• Effective Sealing Function: These seals effectively keep lubricants inside the system while blocking outside contaminants such as dirt, dust, and moisture. This dual action protects vital internal components, particularly rolling element bearings.

• Low Initial Cost: They are generally inexpensive to manufacture and purchase, offering a cost-effective sealing solution.

• Simple Design: Their straightforward design facilitates easy installation and replacement, contributing to reduced labor and maintenance costs.

• Compact Axial Space: Their minimal axial footprint allows for more efficient and smaller machinery designs, which is beneficial in space-constrained applications.

• Reliable Performance in Moderate Conditions & Lower Speeds: They perform reliably in low-to-moderate speed and temperature applications with ample lubrication. Their contact design ensures effective and consistent sealing even at lower operating speeds.

• Wide Operating Temperature Range: Lip seals can operate effectively across a wide temperature range, depending on their material composition. This flexibility makes them suitable for various environmental conditions.

Limitations of Lip Seals

Limited Pressure Capability

Designed only for low to moderate pressure differentials. High pressures can deform the flexible sealing lip, leading to immediate leakage or premature failure.

Friction, Heat, and Wear

• Constant contact with the rotating shaft inevitably causes frictional wear and generates heat. This problem worsens under three main conditions: insufficient lubrication, dirt by abrasive particles, and excessive rotational speed.

• Limited High-Speed Performance: High speeds intensify friction and heat, speeding up wear and compromising sealing integrity.

Sensitivity to Shaft Conditions

Lip seals are highly sensitive to shaft condition, which directly impacts their life and effectiveness.

Problems like an improper surface finish, insufficient hardness, excessive runout, or misalignment can compromise the seal.

In some cases, prolonged use can even lead to the seal causing wear or grooving on the shaft itself, especially when lubrication is poor.

Environmental Limitations

• Temperature Sensitivity: High temperatures, whether from external heat or self-generated friction, can degrade the seal's elastomeric materials. This results in the seal hardening, cracking, or losing its sealing force.

• Sensitivity to Contamination: Though built to exclude contaminants, lip seals are not invincible. The constant entry of heavy or abrasive particles can damage the seal lip or the shaft. This compromises the seal's effectiveness and leads to its early failure.

How Are Lip Seals Represented?

Beyond the industry's standard designations like 2RS, some manufacturers also have their own specific seal codes. See the table below for details.

Exploring Labyrinth Seals in Pillow Block Bearings

What are Labyrinth Seals?

A labyrinth seal is a type of non-contact seal designed to protect bearings in rotating equipment. It consists of two non-contacting rings that form a complex, winding path.

This seal design effectively restricts the ingress of contaminants such as dirt, splashing liquids, or particulate matter.

How Labyrinth Seals Work

• Centrifugal Force Exploitation: As the system rotates, particulates are naturally flung outwards by centrifugal forces. This creates an outward radial force that actively pushes contaminants away from the seal's center.

Fig 5 Centrifugal Force

• Inward-Progressing Labyrinth Path: The seal's internal design, forces contaminants to move radially inward to cross. This means particulates must constantly fight against the outward centrifugal forces.

• Minimized Gap Height: The extremely tight clearance within the seal's gaps significantly increases flow resistance. This strips away any momentum particulates might have, preventing them from carrying enough energy to traverse the seal.

Materials

• Bronze
• stainless steel
• Aluminum Alloy, g. 6061
• Inconel 718
• Thermoplastics:PI(polyamide-imide), PTFE, PEEK

Common Types of Labyrinth Seals

 Fig 6 CF Seal

Fig 7 L Seal

Fig 8 M Seal

Fig 9 S Seal

Fig 10 FA Seal

Advantages of Labyrinth Seals

• True Non-Contact Operation & Zero Wear: The absence of physical contact eliminates friction, wear, and heat generation at the seal interface. This is their fundamental, unique advantage, directly leading to subsequent benefits.

• Exceptional High-Speed & High-Temperature Capability: Since they have no friction or wear, these seals are an excellent choice for extremely high-speed applications. They can also operate effectively in environments that are much hotter than those for contact seals.

• Extended Lifespan & Minimal Maintenance: With no wear, their service lifespan often matches that of the equipment itself. This makes them a lifetime solution that drastically reduces maintenance and eliminates costly downtime for replacement.

• Robust Long-Term Contaminant Exclusion in Harsh Environments: Labyrinth seals don't wear down from contact, so they stay highly effective for a long time. This is why they're great at keeping out airborne particles and splashing liquids, even in dirty, dusty, or abrasive environments.

• No Shaft Wear: Completely prevents any wear or grooving on the shaft, preserving shaft integrity and avoiding expensive repairs.

Limitations of Labyrinth Seals

• No Static Sealing: Labyrinth seals provide minimal to no sealing when the shaft is stationary. Their effectiveness relies on dynamic rotation to restrict fluid flow, making them unsuitable for static fluid retention.

• Limited Pressure & Liquid Sealing: They are ineffective at sealing against significant pressure differentials, particularly with liquids. They function primarily as flow restrictors rather than absolute seals. These seals cannot prevent the egress of standing or pooled liquids.

• Sensitivity to Clearances & Precision: Their efficiency is highly dependent on precise, minimal operating clearances. Deviations because of manufacturing tolerances, thermal expansion, or shaft dynamics (runout, misalignment) drastically reduce sealing effectiveness.

• Vulnerability to Clogging: The intricate passages are susceptible to clogging by heavy or sticky particulate contamination, which can degrade performance or lead to mechanical interference.

• Higher Initial Cost: Achieving the necessary precision for effective operation often requires complex machining and assembly, resulting in a higher initial manufacturing and installation cost.

Direct Comparison: Lip Seal vs. Labyrinth Seal

Choosing the right seal for your pillow block bearing is a critical decision.

Labyrinth seals are ideal for high-speed applications, such as in electric motors and turbines. Their lack of friction provides a major advantage in these environments.

On the other hand, lip seals are a more cost-effective option for general machinery. They offer excellent static sealing and are best for applications with lower speeds and moderate contamination.

Choosing the Right Seal for Your Pillow Block Bearing

Choosing the right seal is vital for your pillow block bearing's longevity.

By carefully considering the operating environment – including speed, temperature, pressure, and the presence of contaminants – alongside the specific advantages and limitations of both lip seals and labyrinth seals, you can ensure optimal protection. 

Contact our technical team today for expert seal solution guidance.