Leading Edge Groove Thrust Bearings
Directed lubrication that improves efficiency, stability, and load capacity in high-performance turbomachinery.
Kingsbury's Leading Edge Groove (LEG®) Thrust Bearing Technology
Engineered for high speed, high load environments
LEG Thrust Bearings were developed for demanding turbomachinery where oil film stability and temperature behavior determine overall machine performance. Kingsbury introduced this design in 1985 after noticing that traditional flooded lubrication wasted energy and carried excess heat into the critical operating areas on the shoe surface. The LEG approach directs cool oil to the leading edge of each pad, protecting the babbitt and maintaining a consistent film under varying load and speed conditions.
NOTE: Model variations, including S-Style and J/B-Style, can be found in the catalog.
How They Work
Each Thrust Shoe incorporates a machined leading edge groove, thus the moniker LEG. Oil enters this groove first, then forms a stable hydrodynamic wedge across the pad. The oil reaches the load zone with minimal disturbance, so the film remains uniform even through load transients. Because the bearing is not operating in a housing chamber flooded with oil, parasitic drag and power loss is reduced. The operator often sees lower oil temperatures, lower system bulk oil flow requirements, and fewer temperature spikes during startups or rapid load changes. The improvement in efficiency often leads to extended bearing life, particularly in high-speed, high-load turbomachinery.
LEG Bearing Performance Highlights
Field data and controlled test rigs have shown that LEG Thrust Bearings can:
• Reduce lubricating oil flow rates compared to standard flooded designs.
• Lower power loss due to reduced oil shearing and minimized parasitic oil drag.
• Reduce operating temperatures through more efficient delivery of cool oil to the operating surface.
• Increase load capacity because the shoe surface is insulated from hot oil carryover.
Operational Advantages
The directed oil wedge provides predictable behavior during startups, shutdowns, and abrupt load swings. Operators report more stable film thickness and fewer nuisance temperature alarms. Lower bulk oil demand can also reduce the lubrication system complexity, since pumps, coolers, and sumps can often be sized accordingly for the reduced oil flow requirements.
Technical Specifications and Design Options of Kingsbury LEG Bearings
Configurations and Materials
LEG Thrust Bearings are available in multiple diameters, pad counts, and pivot styles. Pads are machined to Kingsbury’s precise standards and typically lined with high tin babbitt, although other materials may be used based on temperature or contamination concerns. A spherical pivot design allows for effective pad tilting in a 360 degree range of motion to support optimum oil film development while the inclusion of Kingsbury’s renowned self-equalizing system provides the reliable load distribution that makes the Kingsbury Bearing the most trusted in the industry.
Design Flexibility
Kingsbury engineers can vary groove depth, pad geometry, and oil entry orientation to improve system behavior. The layout supports applications where oil quality is variable, where loads fluctuate, or where shaft endplay needs to be tightly controlled. For applications involving high inlet temperatures, Kingsbury can integrate features to slow heat transfer into the film.
Why Choose Kingsbury for Thrust Bearings?
Trusted Engineering Leadership
For over a century, Kingsbury has defined hydrodynamic bearing innovation. Our founder, Dr.Albert Kingsbury pioneered the original tilting-pad bearing with the first installation in 1912, and today we continue to refine fluid-film technology through ongoing research and collaboration with leading equipment manufacturers in the turbomachinery, power generation and industrial equipment markets.
Comprehensive Support
Kingsbury’s support extends beyond manufacturing. Our engineering teams assist with every phase of the project:
- Bearing selection and system design review
- Retrofit and upgrade consultation
- Installation and alignment assistance
- Field service, inspection, and repair through our global network
With dedicated service centers in the United States and abroad, Kingsbury provides the best support in the business, ensuring long-term performance and reliability for every installation.
Leading Edge Groove (LEG) Thrust Bearings
Advantages of LEG Technology
Kingsbury’s Leading Edge Groove (LEG) bearings are designed to improve load capacity, reduce operating temperature, and lower power loss by delivering cool, undiluted oil directly into the hydrodynamic film. By introducing oil at the leading edge of each shoe, LEG technology prevents hot oil carryover from entering the oil film, resulting in more stable operation and improved bearing performance.
LEG bearings build on Kingsbury’s proven hydrodynamic bearing design and incorporate additional features, such as offset pivots and directed lubrication, to achieve reliable load distribution and long service life. These design elements work together to produce performance advantages over flooded and spray-lubricated bearing designs.
Key Design Features
Several integrated features distinguish LEG bearings from other directed lubrication designs:
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Oil feed tubes connect directly to each shoe, ensuring that cool oil enters the oil film rather than bypassing it
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The leading edge groove is an integral part of the shoe design, not an added component
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Large internal oil passages reduce the risk of clogging associated with small orifices
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Oil seal rings are not required, reducing parasitic losses and simplifying installation
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LEG bearings do not require special high-pressure lubrication systems, though they can operate with them if needed
Because most of the supplied oil is delivered directly into the oil wedge, LEG bearings operate with significantly lower oil flow and reduced power loss. These efficiencies often allow the use of smaller lubrication systems, reducing both operating and capital costs.
Retrofit and New Application Benefits
LEG bearings are well suited for both new installations and retrofit applications. In many cases, existing standard thrust or journal bearings can be replaced with LEG designs using the same housing and oil delivery configuration, often with only minor modifications.
Retrofitting with LEG bearings is an effective solution when operating conditions have changed, loads have increased, or field experience has shown an existing bearing installation to be marginal. Depending on operating speed, replacing standard bearings with LEG designs typically results in immediate reductions in oil flow, power loss, and shoe temperature. With minor adjustments to housing components and oil flow paths, additional performance gains can be achieved.
For both new and retrofit applications, LEG thrust bearings offer the following advantages:
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Lower friction power loss, improving overall machine efficiency
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Lower operating temperatures and increased load capacity
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Reduced oil flow requirements, enabling smaller lubrication systems and lower capital costs
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Flexibility to optimize the bearing design for maximum load capacity or minimum power loss
LEG Bearing Components
Shoes
Kingsbury LEG bearing shoes are designed with offset pivots located at 60% of the effective shoe length. This configuration promotes stable film formation and improved load carrying capability. Standard shoe construction consists of low-carbon steel with high-tin babbitt, though materials can be engineered to meet unusual operating requirements.
Each shoe incorporates a raised spherical support on the back, allowing full 360-degree pivoting. Unlike strip-style pivots that permit motion in only one direction, this spherical support enables self-alignment under load. Shoe supports are manufactured from carbon tool steel and heat treated to 52–57 Rockwell C to resist wear. Testing has shown that this design reduces temperature variation between individual shoes.
Base Ring
The base ring is manufactured from structural steel plate or forged steel and holds the shoes and leveling plates in their operating positions. An oil inlet annulus located at the rear of the base ring distributes oil to axial passages that feed each shoe through the oil feed tubes.
Oil Feed Tube
The oil feed tube connects the base ring to each shoe and is designed to allow the shoe to pivot freely. This design ensures unrestricted shoe movement while directing oil precisely to the shoe face, eliminating leakage paths and ensuring consistent oil delivery to the hydrodynamic film.
Leveling Plate Assembly
Kingsbury’s equalizing leveling plate system allows each shoe to carry an equal share of the total thrust load. The upper and lower leveling plates work in conjunction with the spherical shoe supports to ensure the thrust bearing face aligns accurately with the rotating thrust collar during operation.
LEG Bearings Compared to Flooded and Other Directed Lubrication Designs
Extensive testing and years of field operation have demonstrated that Kingsbury LEG bearings outperform flooded and other directed lubrication bearing designs. While the concept is straightforward, its impact on performance is significant.
LEG bearing shoes and the base ring are configured so that cool inlet oil flows from the leading edge groove directly into the oil film. This cool oil insulates the babbitt surface from hot oil carried over by the rotating collar, resulting in lower operating temperatures and a more stable oil film.
As a result, LEG thrust bearings can:
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Reduce operating temperatures at the 75/75 location by approximately 8 to 28°C, depending on load and shaft speed
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Increase load capacity by 15 to 35%
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Operate at oil flow rates up to 60% lower, with corresponding power loss reductions of up to 45%
Power loss is lower than both flooded and spray-fed bearings due to the elimination of parasitic losses. By maintaining lower shoe surface temperatures, LEG bearings achieve higher load capacity and improved efficiency. These performance improvements are reflected in the accompanying performance curves.
LEG bearings translate directed lubrication into measurable improvements in efficiency, reliability, and operating margin. Backed by decades of field experience and testing, this technology allows designers and operators to address rising loads, thermal limits, and system efficiency with confidence.
Contact Kingsbury to discuss your application or review LEG bearing options.
Industries and Systems Served
Kingsbury LEG thrust bearings operate in environments where efficiency, oil control, and thermal stability are critical. They are installed worldwide in systems such as:
- Gas and steam turbines used in power generation and industrial processes.
- Compressors and pumps supporting oil and gas operations
- Marine propulsion systems across commercial and military fleets
- Industrial gearboxes and turboexpanders
- High-speed test stands and rotating machinery laboratories
Their versatility and documented performance have made LEG bearings a preferred choice for OEMs and retrofit specialists across global rotating equipment markets.
Retrofit or Upgrade Scenarios
LEG bearings are an effective upgrade for older flooded-lubricated systems that are running close to their thermal limits. The directed lubrication and leading-edge groove geometry help reduce oil flow requirements and distribute load more effectively, which allows many retrofits to be completed without major changes to the thrust bearing assembly.
A well-planned LEG retrofit often delivers clear improvements:
• Lower operating temperatures
• Reduced demand on the lube system
• Higher overall efficiency and improved uptime
Kingsbury’s engineering and field service teams support every retrofit with proper fit checks, alignment guidance, and commissioning support to ensure the bearing performs as intended over the long term.
Retrofit or Upgrade Scenarios
LEG bearings are an effective upgrade for older flooded-lubricated systems that are running close to their thermal limits. The directed lubrication and leading-edge groove geometry help reduce oil flow requirements and distribute load more effectively, which allows many retrofits to be completed without major changes to the thrust bearing assembly.
A well-planned LEG retrofit often delivers clear improvements:
• Lower operating temperatures
• Reduced demand on the lube system
• Higher overall efficiency and improved uptime
Kingsbury’s engineering and field service teams support every retrofit with proper fit checks, alignment guidance, and commissioning support to ensure the bearing performs as intended over the long term.
