NCCER Millwright Practice Exam

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What is the base composition of most hydraulic fluids?

Water-based
Petroleum oil-based
Alcohol-based
Biodegradable fluid

The correct answer is: Petroleum oil-based

The base composition of most hydraulic fluids being petroleum oil-based is significant because petroleum oils offer excellent lubrication properties, thermal stability, and resistance to oxidation, which are critical for ensuring efficient operation and longevity of hydraulic systems. Petroleum-based hydraulic fluids can handle high pressures and are effective at transferring power in hydraulic machinery. In contrast, water-based fluids, while often used for specific applications, tend to have limitations such as lower lubricating properties and a higher potential for corrosion and cavitation. Alcohol-based fluids are less common in industrial settings, primarily due to issues with flammability and lower lubricating qualities. Biodegradable fluids are becoming more prevalent due to environmental concerns, but they are not as widely used in conventional hydraulic systems compared to petroleum-based options. Overall, the widespread use of petroleum oil-based hydraulic fluids is attributed to their performance attributes that make them suitable for a variety of industrial applications.