Practice Test Geeks(CLS) Certified Lubrication Specialist Practice Test
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Lubrication Fundamentals & Applications Flashcards

7 cards from real CLS practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

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  1. Which lubrication regime is characterized by complete separation of surfaces by a full fluid film?

    Answer: Hydrodynamic lubrication

    Hydrodynamic lubrication occurs when a full fluid film completely separates the mating surfaces, eliminating metal-to-metal contact.

  2. What does the Stribeck curve illustrate?

    Answer: The friction coefficient across different lubrication regimes as a function of speed and viscosity

    The Stribeck curve plots friction coefficient against the ratio of viscosity × speed / load, showing transitions between boundary, mixed, and full-film lubrication regimes.

  3. What is the primary purpose of an EP (Extreme Pressure) additive in a lubricant?

    Answer: To chemically react with metal surfaces under high pressure to prevent welding

    EP additives form sacrificial chemical films on metal surfaces at high contact pressures, preventing scuffing and welding of asperities.

  4. Which property of a grease describes its resistance to flow and is measured by a cone penetration test?

    Answer: Consistency (NLGI grade)

    NLGI consistency grade, determined by cone penetration depth, classifies grease firmness from 000 (very fluid) to 6 (very hard).

  5. What is meant by the 'viscosity index' (VI) of a lubricant?

    Answer: A measure of how much viscosity changes with temperature

    Viscosity index indicates the rate of viscosity change with temperature; a higher VI means less viscosity change over a given temperature range.

  6. In boundary lubrication, what primarily prevents surface damage?

    Answer: Adsorbed or chemically reacted films on the asperities

    In boundary lubrication, thin molecular films (adsorbed layers or reaction products from additives) on asperity tips carry the load and prevent welding.

  7. Which base oil group, per API classification, is produced by the hydrocracking process and offers improved VI and oxidation stability over Group I oils?

    Answer: Group II

    API Group II base oils are produced via hydrocracking, resulting in higher VI and lower sulfur content than solvent-refined Group I oils.