CLS Case Analysis & Practical Application 2 — Questions and Answers
Question 1: A conveyor drive gearbox operating in a food processing plant shows elevated iron particles in oil analysis. The plant requires H1-rated lubricants. Which corrective action is most appropriate?
- Switch to a higher-viscosity H1-rated gear oil and monitor wear trend (Correct answer)
- Immediately drain and refill with a standard ISO 220 gear oil
- Add an aftermarket EP additive package to extend oil life
- Increase oil change frequency to weekly regardless of analysis results
Correct answer: Switch to a higher-viscosity H1-rated gear oil and monitor wear trend
Selecting a higher-viscosity H1-rated gear oil addresses the wear trend while maintaining food-safety compliance, and monitoring confirms whether the change is effective.
Question 2: An electric motor bearing running at 3600 RPM is being re-greased. The technician notices the grease fitting is packed solid with hardened grease. What is the best first step?
- Apply high pressure to force new grease through the blockage
- Clean and clear the fitting before introducing fresh grease (Correct answer)
- Replace the bearing immediately since contamination has occurred
- Switch to oil mist lubrication without further inspection
Correct answer: Clean and clear the fitting before introducing fresh grease
A blocked fitting must be cleared first so new grease actually reaches the bearing; forcing grease through a blockage can over-pressurize seals.
Question 3: Oil analysis on a hydraulic system reveals a particle count of ISO 23/21/17. The system specification calls for ISO 16/14/11 cleanliness. What action should be taken?
- Flush the system and pass fluid through a kidney-loop filtration unit until target cleanliness is reached (Correct answer)
- Accept the current cleanliness level since hydraulic systems tolerate high particle counts
- Change only the return filter and retest in 90 days
- Increase pump pressure to expel contaminants through the relief valve
Correct answer: Flush the system and pass fluid through a kidney-loop filtration unit until target cleanliness is reached
Offline (kidney-loop) filtration is the most effective method to rapidly reduce particle counts to the target ISO cleanliness code.
Question 4: A plant engineer notices that two similar compressors have very different oil consumption rates. Compressor A uses twice the oil of Compressor B despite identical operating hours. What is the most likely root cause to investigate first?
- Compressor A has a higher ambient temperature
- Compressor A has worn piston rings or valve seals causing oil carry-over (Correct answer)
- Compressor A uses a lower-viscosity oil grade
- Compressor B has an oversized sump
Correct answer: Compressor A has worn piston rings or valve seals causing oil carry-over
Worn piston rings or valve seals allow oil to pass into the gas stream, dramatically increasing oil consumption in reciprocating compressors.
Question 5: During a lubrication audit, a technician finds that multiple lube routes mix NLGI 2 lithium-complex grease and NLGI 2 polyurea grease in the same bearing housings. What is the primary concern?
- Polyurea greases always cost more and inflate maintenance budgets
- Incompatible thickener systems can cause grease softening and loss of lubrication (Correct answer)
- Lithium-complex grease cannot be used in electric motor bearings
- Mixing two NLGI 2 grades always causes over-lubrication
Correct answer: Incompatible thickener systems can cause grease softening and loss of lubrication
Lithium-complex and polyurea thickeners are often incompatible, and mixing them can cause the grease structure to collapse, leading to lubrication failure.
Question 6: A plant switches from mineral oil to a polyalkylene glycol (PAG) fluid in a worm gear drive. What precaution is most critical before filling?
- Increase the oil change interval since PAG fluids last longer
- Thoroughly flush residual mineral oil because PAG and mineral oil are immiscible (Correct answer)
- Add a VI improver to achieve the correct viscosity
- Cool the gearbox to below 40°C before adding PAG fluid
Correct answer: Thoroughly flush residual mineral oil because PAG and mineral oil are immiscible
PAG fluids are incompatible with mineral oils and will form sludge if mixed, so thorough flushing is mandatory before filling.
Question 7: Vibration analysis on a pump bearing shows a spike at bearing defect frequency corresponding to the outer race. Oil analysis shows no elevated metals. Which lubricant-related issue should be investigated?
- Excessive oil viscosity causing churning losses
- Inadequate grease quantity leading to inadequate film formation on the outer race (Correct answer)
- High water content in the oil causing corrosion on inner race
- Over-lubrication forcing grease into the motor windings
Correct answer: Inadequate grease quantity leading to inadequate film formation on the outer race
An outer-race defect without metallic wear particles suggests inadequate film thickness rather than active corrosive wear, pointing to insufficient lubrication.
CLS Case Analysis & Practical Application 2
A conveyor drive gearbox operating in a food processing plant shows elevated iron particles in oil analysis.
The plant requires H1-rated lubricants.
Which corrective action is most appropriate?