Which of the following is NOT a type of lubrication used in machinery?

Water lubrication is typically not classified as a conventional type of lubrication used in machinery. Most lubricants are used to reduce friction, wear, and heat between moving parts, and are designed to form a barrier that prevents direct contact between surfaces.

Oil and grease lubrication are the most common types, designed to coat surfaces and provide a film that resists wear and heat. Oil lubrication involves the use of liquid petroleum products, while grease is a thicker formulation that combines oil with a thickening agent, making it suitable for applications where a longer-lasting film is needed.

Air lubrication, while less common, is a method that can reduce friction by creating an air barrier between surfaces, particularly in applications like high-speed bearings.

In contrast, water lubrication is not generally effective for machinery because water does not provide the necessary protective films to withstand the conditions within most machine operations, such as high temperatures and pressures. Thus, it is not considered a standard lubrication method in the same way that oil, grease, and air are.