Case Analysis & Practical Application Flashcards

A plant engineer is selecting a lubricant for an open gear drive on a kiln operating at 300°F (149°C) ambient surface temperature. Which lubricant type is most appropriate?

Answer: A high-viscosity asphaltic or synthetic open-gear compound with adhesive/film-forming properties

Open gear compounds are specifically formulated with high-viscosity adhesive carriers and extreme-pressure additives to cling to gear flanks under high temperatures and shock loads.

Oil analysis on a reciprocating air compressor shows rapidly increasing silicon levels over three consecutive samples. What is the most likely source?

Answer: Airborne silica dust ingesting through a damaged or missing inlet air filter

Rising silicon in compressor oil is a classic indicator of airborne silica (dust/dirt) ingestion due to a compromised inlet filtration system.

A technician is greasing a pillow-block bearing on a slow-speed (10 RPM) conveyor carrying heavy aggregate. The current NLGI 2 grease shows excessive leakage. Which change would best address this?

Answer: Use an NLGI 3 or NLGI 4 grease with higher consistency to reduce leakage under high load

Stiffer grease (NLGI 3–4) resists leakage better under heavy radial loads and slow-speed conditions where grease tends to slump out of the bearing.

After a plant flood, a large quantity of oil-lubricated equipment was submerged for several hours. The maintenance team finds oil samples from several gearboxes look milky. What is the correct first step?

Answer: Immediately drain and flush each gearbox, replacing with fresh lubricant after thorough inspection

Milky (emulsified) oil indicates significant water contamination that destroys lubricant film; the oil must be drained, the system flushed, and fresh lubricant installed before operating.

A CLS candidate is evaluating a wind turbine main gearbox that consumes significantly more oil than identical turbines in the same wind farm. Particle count analysis is normal. What should be checked next?

Answer: Inspect breather/vent condition and gear housing seals for external leakage paths

Normal particle counts rule out internal wear as the cause of oil loss; the most logical next step is identifying external leakage through seals, breathers, or drain plugs.

A 500 HP induction motor driving a centrifugal pump is found to have a bearing temperature of 210°F (99°C) on re-grease day. The spec limit is 180°F (82°C). The technician has just re-greased the bearing. What is the most likely immediate cause of the temperature spike?

Answer: The bearing was over-greased, causing churning and heat generation

Immediately after re-greasing, a temperature spike is most commonly caused by over-greasing; excess grease causes the rolling elements to churn the lubricant, generating heat until surplus grease purges.

A plant is implementing a predictive maintenance program. Infrared thermography on a chain drive shows a hot spot on one chain link section. Oil analysis is not applicable here. What lubrication action should be taken?

Answer: Inspect that chain section for a stiff or seized link and apply chain lubricant to relieve friction

A localized hot spot on a chain indicates a stiff or seized link, which is typically caused by lubricant starvation or contamination and should be addressed with cleaning and lubrication before replacement.