LDK Bearings - Professional bearing manufacturer for all kinds of bearing unit since 1986 


What are Plummer Block Bearings and How Do They Work?

Plummer block bearings, also known as pillow block bearings, are a critical component in a wide range of industrial machinery and mechanical systems. As one of the most common types of anti-friction bearings, understanding the design and function of plummer block bearings is essential for engineers, technicians, and anyone involved in the installation, maintenance or repair of rotating equipment. This article provides an in-depth look at what plummer block bearings are, their key components, how they work, maintenance best practices, common applications, advantages and disadvantages, and more. With the insights provided here, you will have a well-rounded knowledge of these ubiquitous bearings and their role in reducing friction in mechanical systems.


What are Plummer Block Bearings?


Plummer block bearings are a type of housed bearing unit that consists of a bearing inserted in a plummer block housing. The plummer block housing is typically made of cast iron or steel and acts as an enclosure and mounting for the bearing. Within the housing, the actual bearing is usually a ball bearing or roller bearing that has inner and outer races and rolling elements that reduce friction between the spinning shaft and stationary housing. Together, the housing and internal bearing help support and locate a rotating shaft while enabling free rotation and reduced friction.


There are several types of plummer block bearings suitable for different applications, loads, and operating conditions. Common varieties include split housing, flanged housing, take-up housing, and eccentric locking collar plummer blocks. Factors like required rigidity, shaft size, lubrication needs, and operating environment will determine the optimal plummer block type for a given application. Their versatility makes them a workhorse bearing choice for industrial rotating machinery.


Design and Components of Plummer Block Bearings


The main components that make up a plummer block unit are the housing, the bearing inside the housing, seals to keep contaminants out, and the locking collar or mounting for securing the bearing.


Housing: Made of cast iron or steel, the housing provides an enclosure and structure for mounting the bearing and connecting it to equipment. The housing includes a base with holes for bolting to a foundation plus a bore to insert the bearing.


Bearing: Typically a ball or roller bearing, the internal bearing supports the shaft and allows low-friction rotation. Common options are deep groove ball bearings, spherical roller bearings, tapered roller bearings, and cylindrical roller bearings.


Seals: Seals such as o-rings and rubber lip seals are used to keep lubricant in and contaminants like dirt and moisture out of the housing.


Locking Collar: A locking collar or flange keeps the bearing securely seated inside the housing. Tightening the collar properly preloads the bearing for optimal internal clearance.


Proper housing design, internal bearing selection, sealing, and locking collar preload all contribute to optimal performance and service life of plummer block bearings. Material selection, dimensional tolerances, and lubrication provisions also require careful engineering attention.


How Do Plummer Block Bearings Work? 


In operation, plummer block bearings support rotating shafts while minimizing friction between the stationary housing and rotating shaft. This is achieved through the internal bearing’s rolling elements positioned between inner and outer races.


As the shaft spins, the inner race of the bearing rotates with the shaft. The outer race stays fixed in the housing. The rolling balls or rollers between the races roll with low friction rather than sliding friction. This rolling contact greatly reduces friction, heat, and power loss versus direct shaft-to-housing contact.


With proper preload from the locking collar, optimal radial and axial clearance is maintained between the inner and outer races. This prevents play or excessive clearance that could allow vibration, instability, or damage. The rolling elements ride smoothly even under load, extending the service life of both the bearing and shaft.


Plummer block bearings take radial and axial loads off of the rotating shaft, creating smooth, stable, and reliable performance. Given proper installation and maintenance, these housed bearing units will provide many years of trouble-free operation in even harsh industrial environments.


Maintenance and Troubleshooting 


To keep plummer block bearings operating properly over long service lives, regular maintenance is recommended. The key maintenance tasks include:


- Inspecting bearings for visible damage and checking for looseness or excessive play

- Cleaning the exterior housing and checking for corrosion

- Greasing according to the manufacturer’s instructions to replenish lubricant

- Checking seals for wear and replacing if damaged to prevent contaminant ingress

- Checking preload and re-tightening collars if needed

- Checking mounting bolt torque to ensure firm anchoring


Potential issues to watch out for include excessive noise or vibration, high operating temperatures, loose collars, lubricant leakage, and seals allowing contaminant entry. Diagnosing the root cause early allows preventative action to be taken before severe damage occurs. Bearings should be replaced once wear exceeds allowable tolerances.


Applications of Plummer Block Bearings


Plummer block bearings have broad application across many heavy industries where rotating equipment is found. Some common applications include:


- Electric motors - Used to support motor shaft rotation

- Pumps - Support pump shafts in water pumps, chemical pumps, etc.

- Conveyors - Locate rollers in conveyor systems

- Gearboxes - Support input or output shafts

- Fans & Blowers - Enable fan shaft rotation in air handlers

- Mixers - Used in blenders, agitators, tumblers

- Machine Tools - Support spindles for rotation accuracy

- Rollers - Enable precise rotation in rolling mills and calenders

- Compressors - Bearings support compressor shaft rotation


In these and many other industrial contexts, plummer block bearings provide a sturdy, reliable housed bearing solution.


Advantages and Disadvantages of Plummer Block Bearings


Some key advantages of plummer block bearings include:


- Enclosed housing protects internal bearing from contaminants

- Rigid, heavy-duty housing and collar provide stable shaft support

- Variety of bearing types to suit different loads and speeds

- Re-lubrication possible via grease fittings to extend life

- Easily inspected without full machine disassembly

- Interchangeable and replaceable to minimize downtime

- Cost-effective and readily available


Potential disadvantages include:


- Housing takes up more space than an unhoused bearing

- Restricted heat dissipation from enclosed housing

- Seals can fail over time, limiting bearing life

- Collar preload loss can occur over time or from mishandling

- Housing limits high speed capability of internal bearings

- More expensive than basic unhoused bearings


Proper selection, installation, and maintenance helps maximize the excellent performance plummer block bearings can provide in industrial machinery.



Plummer block bearings are an indispensable component that allow reliable shaft rotation under load in a wide range of mechanical equipment. Their split or flanged housing encloses and locates either a ball bearing or roller bearing that has inner and outer races with rolling elements in between. This bearing arrangement supports radial and axial loads while minimizing rotational friction for smooth, efficient performance. Given proper specification, installation, lubrication, and maintenance, plummer block bearings will provide many years of trouble-free operation. Their heavy-duty housed design protects internal bearings in harsh environments for reduced downtime and costs. Understanding proper sizing, installation, and care of plummer block bearings gives engineers, technicians and operators the knowledge needed to apply these bearings most effectively.


At Deyuan Smart Technology, we take great pride in the recognition our product quality and services have garnered from customers in the industry. We strive to provide exceptional products and services that meet and exceed customer expectations. You can trust us as your reliable partner in the pillow blocks industry. For further inquiries or to discuss your specific requirements, please contact kzhang@ldk-bearings.com or call +86-592-580 7618. We look forward to the opportunity to work with you.




1. Bhadeshia, Harshad K. D. "Plummer Block Bearings and Their Lubrication." University of Cambridge, 2013, pp. 1–4, Plummer Block Bearings and Their Lubrication.


2. Brent, Derrick. "Plummer Blocks & Bearing Housings." AZoM.com, 13 Dec. 2001


3. Budynas, Richard G., et al. Shigley's Mechanical Engineering Design. McGraw-Hill Education, 2020.


4. "Plummer Blocks and Bearing Housings Information." IHS Engineering360, 


5. Sharma, P. C. A Text Book of Production Engineering. S. Chand, 2014.

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