Hydrodynamic Theory of Lubrication | Definition and Meaning.

Hydrodynamics theory of lubrication depends on fluid mechanics. In this article, I will discuss the meaning and advantages of the hydrodynamic theory of lubrication.


Hydrodynamic Theory of Lubrication

Hydrodynamic Theory of Lubrication

Among various theories of lubrication, the hydrodynamic theory stands out as a cornerstone in understanding the mechanisms behind optimal lubricant performance.
The Hydrodynamic Theory of Lubrication is a fundamental concept that elucidates how lubricants work between moving surfaces to reduce friction and wear. Unlike boundary lubrication, where direct contact between surfaces is prevented by a thin film of lubricant, hydrodynamic lubrication relies on the principle of fluid dynamics.
Fluid dynamics play a crucial role in hydrodynamic lubrication. When two surfaces move relative to each other, a lubricating fluid, often an oil-based substance, is introduced into the gap between them. As the surfaces move, they create pressure gradients within the fluid, leading to the formation of a continuous lubricating film. This film separates the surfaces and prevents them from coming into direct contact.

Definition of Hydrodynamic Theory of Lubrication

Definition of Hydrodynamic Theory of Lubrication


When the shaft rotates in a bearing, it takes an eccentric position in the bearing, as shown in the figure. This is due to the loading of the journal W and the direction of rotation.
The oil film is maintained by the wedging action as the oil is forced into the wedge at the bottom by the pressure generated when the oil is carried from the wide space A and forced into the narrow space B at the bottom by rotating the journal to which the oil adheres. This is called the hydrodynamic theory of lubrication.  

Meaning of Hydrodynamic Theory of Lubrication.

From the above there, it is clear that the oil film is maintained only when the journal is in motion. When the journal comes to rest the oil film is squeezed out. When the engine is first started, boundary lubrication comes into play until the oil film is built up by rotating the journal.
The qualities of lubricant called adhesiveness and film strength, help the lubricant to enter the metal ports and cling to the surfaces of the bearing and journals keeping them wet when the journals are at rest, preventing metal contact until the film of lubricant is built up. 

Advantages of Hydrodynamic Theory of Lubrication

The Hydrodynamic Theory of Lubrication offers numerous advantages over other lubrication theories, making it the preferred choice in many industrial applications:
  1. This lubrication system can significantly resist the friction of two moving parts.
  2. Hydrodynamic theory can extend machinery lifespan.
  3. Due to the formation of a continuous lubricating film, hydrodynamic lubrication can support heavy loads without experiencing direct metal-to-metal contact.
  4. Hydrodynamic lubrication reduces the impact of vibration damping.
  5. The lubricating film acts as a protective barrier, preventing contaminants such as dust, dirt, and debris from reaching critical surfaces.


Routine maintenance of lubrication systems ensures that the fluid properties remain within the desired range, and any potential issues are detected and addressed promptly.


The Hydrodynamic Theory of Lubrication stands as an indispensable concept in the realm of engineering and machinery. Its ability to reduce friction, dissipate heat, and withstand heavy loads makes it an optimal choice for various industrial applications.
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