Pillow Block Bearing Seals: Lip vs. Labyrinth Guide

Pillow block bearings support rotating shafts in conveyors, fans, pumps, agricultural machinery and many other industrial machines. Their service life depends heavily on the seal, which keeps grease in and keeps dust, water and debris out.

There are several bearing seal types. This guide compares the two most common choices for pillow blocks: contact lip seals and non-contact labyrinth seals.

Lip Seal vs Labyrinth Seal: Quick Answer

• Choose a lip seal when shaft speed is low to moderate, you need reliable sealing at standstill, and cost matters.

• Choose a labyrinth seal when speed is high or contamination is heavy and you want a seal that does not wear. Grease-packed designs work best.

• Choose a combination seal (labyrinth plus lip, or a taconite-style seal) for very abrasive or wet conditions such as mining, aggregate handling and cement plants.

• For washdown areas, use multi-lip seals in corrosion-resistant housings rather than relying on an open labyrinth (see the selection table below).

Already know your shaft size? Use our size chart to find the right UCP unit

How seals are fitted: Many standard UCP-type units use insert ball bearings that already have integral contact seals, often with an outer flinger. Heavier plummer block housings (such as SN and SNL types) with spherical roller bearings use separate housing seals, including felt, lip, V-ring, labyrinth and taconite designs. The guidance below applies to both, but the shaft requirements differ, as explained in the lip seal section.

Understanding Lip Seals in Pillow Block Bearings

What Are Lip Seals?

A lip seal, also called a radial shaft seal or rotary shaft seal, is a contact seal for rotating shafts. A flexible elastomer lip presses against the rotating surface and blocks the path of lubricant out and contaminants in. Dimensions and requirements for rotary shaft lip seals are covered by ISO 6194, and DIN 3760 is still widely referenced.

Fig 1 Contact Seal

A thin lubricant film forms between the lip and the rotating surface. This film is essential: it reduces friction and wear, and a lip seal that runs dry can overheat and fail quickly.

Most lip seals combine a metal or rubber-covered case with an elastomer sealing lip. Many designs add a garter spring to maintain consistent contact pressure.

Types of Lip Seals

Single-Lip Seal

One lip retains lubricant with limited dust protection. It is the lowest-cost option, suited to light-duty, low-contamination applications such as some conveyor idlers.

Fig 2 Single Lip Seal

Double-Lip Seal

The main lip retains grease or oil, while a secondary (dust) lip keeps dirt out. This is a common choice for agricultural and general industrial equipment.

Fig 3 Double Lip Seal

Triple-Lip Seal

An additional lip, often with grease-filled cavities between the lips, adds a further barrier. It is used in dusty, wet or abrasive environments such as mining and aggregate handling.

Fig 4 Triple Lip Seal

Common Materials of Lip Seals

The lip material decides the temperature range and the lubricants and chemicals the seal can tolerate. Typical values are shown below.

Note: Ranges are typical catalog values and vary by compound. The sealing lip usually runs hotter than the housing because of friction, so always confirm limits and grease compatibility with the seal manufacturer's datasheet.

Advantages of Lip Seals

• Effective sealing, including at standstill: Lip seals keep grease in and block dust and moisture whether the shaft is turning or stopped.

• Low initial cost: They are inexpensive to manufacture and buy.

• Simple design: Installation and replacement are straightforward, which keeps labor and maintenance costs down.

• Compact axial space: The small axial footprint suits space-constrained designs.

• Reliable at low to moderate surface speeds: With adequate lubrication, they perform consistently in these conditions.

• Wide material choice: The right elastomer covers a broad range of temperatures and media.

Limitations of Lip Seals

Limited Pressure Capability

Standard rubber-lip designs tolerate only very small pressure differences, typically about 0.05 MPa (roughly 7 psi). Higher pressure presses the lip harder against the shaft, raising friction and heat, and can cause leakage or early failure. Pillow block housings normally run near atmospheric pressure, so this mainly matters with high-pressure washdown or pressurized environments.

Friction, Heat and Wear

Constant contact causes frictional wear and heat. The problem worsens with insufficient lubrication, abrasive contamination and high surface speed.

Speed limits depend on shaft surface speed, not rpm alone: v (m/s) = π × d × n / 60,000, where d is the shaft diameter in mm and n is the speed in rpm. Catalog limits are on the order of 10 to 15 m/s for standard NBR seals and higher for FKM and PTFE designs. For example, a 50 mm shaft at 1,800 rpm runs at about 4.7 m/s, well within the range of standard lip seals.

Sensitivity to Shaft Condition

How the seal is fitted changes the requirements. In insert-type units, the lip normally rides on the hardened, ground inner ring, so ordinary commercial shafting is acceptable. Where a separate housing seal runs directly on the shaft, the shaft becomes the sealing surface. Seal manufacturers typically call for a hardened surface (roughly 45 HRC or more, harder for abrasive conditions), a fine ground finish (about Ra 0.2 to 0.5 µm) without spiral lead marks, and limited runout. Always follow the seal manufacturer's data.

Poor surface finish, insufficient hardness, excessive runout or misalignment can all compromise the seal. With poor lubrication, the lip can even wear a groove into the shaft.

Environmental Limitations

• Temperature: High ambient or friction-generated heat can harden and crack the elastomer, and the lip loses its sealing force.

• Contamination: Heavy or abrasive particles can damage the lip or the shaft, leading to early failure.

Common Contact-Seal Designations on Bearings

Bearing designations show which seal is fitted. The codes are manufacturer-specific, so confirm the meaning in the supplier's catalog. Common examples are listed below.

Exploring Labyrinth Seals in Pillow Block Bearings

What Are Labyrinth Seals?

A labyrinth seal is a non-contact seal. One part turns with the shaft and the other stays fixed in the housing, and together they form a narrow, winding gap. Because nothing touches, there is no friction, heat or wear at the seal.

The winding gap makes it difficult for dirt, splashing liquid and particles to pass. In pillow blocks the labyrinth cavity is usually packed with grease. The grease blocks the gap and is pushed slowly outward each time the bearing is relubricated, carrying contaminants with it (purging).

How Labyrinth Seals Work

• Centrifugal force: As the shaft rotates, particles and liquid on the rotating part are flung outward, away from the bearing.

• Winding path: Contaminants must travel through a path with several direction changes, and often radially inward against the centrifugal effect.

• Tight clearance: The very small gaps raise flow resistance, so particles lose the energy they need to get through.

• Grease packing: Filling the cavity with grease improves exclusion and allows purging during relubrication.

Fig 5 Centrifugal Force

Materials

• Bronze

• Steel and stainless steel

• Aluminum alloy (e.g., 6061)

• Engineering plastics: polyamide-imide (PAI), PTFE compounds, PEEK

• Nickel alloys (e.g., Inconel 718) for extreme-temperature turbomachinery, rarely needed in pillow blocks

Common Types of Labyrinth Seals

The codes below (CF, L, M, S and SA) are product-family designations that illustrate the main labyrinth geometries. Other manufacturers use different codes, so compare geometry and ratings rather than the letters.

Fig 6 CF Seal

Fig 7 L Seal

Fig 8 M Seal

Fig 9 S Seal

Fig 10 SA Seal

Advantages of Labyrinth Seals

• No contact, no wear: There is no friction, heat or wear at the seal, and the shaft or inner ring is never worn by the seal.

• High-speed capability: The seal itself has no friction-based speed limit. The practical limit comes from the bearing and lubricant.

• Long life with little maintenance: With no wearing parts, seal life is governed by the bearing, the grease and whether clearances stay intact.

• Strong dust and splash exclusion in dirty environments: Performance stays consistent over time, especially when the cavity is grease-packed and purged.

• Higher temperature capability at the seal: Metal and high-performance plastic parts tolerate more heat than elastomers. In practice the grease and bearing set the limit.

Limitations of Labyrinth Seals

• Limited sealing at standstill: When the shaft stops, dust and liquid can creep in. Grease packing and drain features help but do not eliminate the risk.

• No pressure or standing-liquid sealing: A labyrinth restricts flow rather than sealing absolutely. It cannot hold back pressure differences or pooled liquid.

• Not a washdown solution on its own: High-pressure water jets can be driven through a non-contact gap, particularly when the shaft is stationary.

• Sensitivity to clearance and alignment: Performance depends on small, consistent gaps. Tolerances, thermal expansion, runout, misalignment or bearing wear can reduce effectiveness.

• Clogging: Heavy or sticky debris can block the passages. Regular grease purging helps.

• Higher cost and more axial space: Precision machining and a wider seal envelope usually make labyrinth seals more expensive than lip seals.

Other Pillow Block Seal Options

• Felt seals: Economical and simple, for light duty, low speed and dry, indoor conditions. They offer limited protection against fine dust and moisture.

• V-ring seals: A rubber ring that rotates with the shaft and seals axially against a face. It is often used as an outer excluder in front of a lip seal.

• Taconite and combination seals: Multi-stage designs that combine labyrinth paths, lips and grease chambers for the most abrasive and wet conditions, such as mining, aggregate and cement handling. Ask the supplier for the rating for your duty.

Direct Comparison: Lip Seal vs Labyrinth Seal

Labyrinth seals suit higher speeds and dirty environments such as fans, blowers and motors, because they do not wear. Lip seals suit lower speeds and offer good sealing at standstill at lower cost. Many pillow block housings combine both.

Note: Figures are typical values for guidance. Confirm limits with the manufacturer's datasheet for your specific seal and lubricant.

Choosing the Right Seal for Your Pillow Block Bearing

Work through these factors in order:

• Surface speed: Calculate v = π × d × n / 60,000 and compare it with the seal's rated limit.

• Contamination: Identify the type (dry dust, wet abrasive, water spray) and how heavy it is.

• Temperature: Check the seal material, the grease and the bearing, not just the seal.

• Standstill: Frequent starts and stops or long idle periods favor contact seals.

• Washdown: Decide whether the unit sees direct spray, and at what pressure.

• Shaft and mounting: Check finish, hardness and runout for lip seals, and clearances and alignment for labyrinth seals.

For washdown and corrosive environments, see our stainless steel bearings and browse our mounted bearings.

Frequently Asked Questions

Is a labyrinth seal better than a lip seal?

Neither is better in every case. Labyrinth seals suit higher speeds and dirty environments because they do not wear, while lip seals seal better at standstill and cost less. Many heavy-duty pillow blocks use both together.

Which seal is best for washdown environments?

Multi-lip contact seals in corrosion-resistant housings, with a flinger and a compatible food-grade grease, are the usual starting point. An open labyrinth can let high-pressure spray through, especially when the shaft is stopped. Verify the IP rating for your conditions and relubricate after washdown.

Can I use a lip seal and a labyrinth seal together?

Yes. Combination and taconite-style seals place a labyrinth stage outside a lip stage, with grease between them. The labyrinth keeps out most of the contamination, and the lip provides sealing at standstill.

What is the difference between contact and non-contact bearing seals?

Contact seals, such as lip seals, touch the rotating surface. They seal well but create friction, heat and wear. Non-contact seals, such as labyrinth seals and shields, leave a small gap. They do not wear but offer less complete sealing.

Do labyrinth seals need grease?

The seal itself needs no lubrication, but the bearing always does. In pillow blocks the labyrinth cavity is normally filled with grease, which improves sealing and allows contaminants to be purged during relubrication.

How do I calculate shaft surface speed?

Use v (m/s) = π × d × n / 60,000, with d in mm and n in rpm. A 50 mm shaft at 1,800 rpm gives about 4.7 m/s.

Not sure which seal your application needs? Send us your shaft size, speed, temperature and operating environment, and our engineers will help you choose. Contact our technical team or request a quote.