Which of the following is NOT one of the three main types of lubrication systems?

The classification of lubrication systems typically includes three main types: centralized lubrication systems, circulating lubrication systems, and lubrication methods that are commonly described as manual application. Each of these systems serves specific functions and is designed for different applications within machinery.

Centralized lubrication systems are designed to distribute lubricant automatically to multiple lubrication points in machinery, which helps ensure consistent application and reduces the need for manual intervention. Circulating lubrication systems utilize a pump to circulate lubricant through the system, ensuring proper lubrication for moving parts and effective removal of contaminants.

Manual application of lubricant, while not a system in itself, represents a common practice used in various scenarios where automated systems are not feasible. It is particularly useful for smaller machines or in maintenance where immediate lubrication is required.

In contrast, hydraulic lubrication systems, while both hydraulic and lubrication functions can coexist in specific machinery, do not represent one of the main types of lubrication systems on their own. Hydraulic systems focus primarily on controlling movement and power within a machine rather than serving directly as a lubrication medium essential for the preventive maintenance of machine components. Therefore, it does not fit into the standard classification of lubrication systems categorized mainly by their automatic or manual operation.