CLS Case Analysis & Practical Application 3 — Questions and Answers
Question 1: A lube tech is sampling oil from a turbine that operates at 65°C. The sample is taken when the unit is shut down and the oil temperature has dropped to 25°C. What is the main concern with this sampling approach?
- Cold oil may not flow properly through the vacuum pump sampler tube
- Contaminants and wear particles settle when oil is cold, making the sample unrepresentative (Correct answer)
- The viscosity increase at 25°C may damage the sample bottle
- Turbine oils must always be sampled above 80°C
Correct answer: Contaminants and wear particles settle when oil is cold, making the sample unrepresentative
Particles settle rapidly in cool, static oil, so a cold-oil sample will under-report contamination and wear compared to a sample taken at operating temperature.
Question 2: A centrifugal pump handling a corrosive chemical slurry has its bearing housing redesigned to use sealed-for-life bearings pre-packed with grease. Six months later failures begin. What is the most probable cause?
- The sealed bearings are not compatible with the high-speed pump application
- Heat and vibration have degraded the factory grease charge faster than anticipated (Correct answer)
- The pump housing material reacts with the grease thickener
- Sealed bearings cannot be used in any pump application
Correct answer: Heat and vibration have degraded the factory grease charge faster than anticipated
Sealed-for-life bearings rely on a fixed grease charge that can degrade under elevated temperatures and vibration, causing premature failure when the grease life is shorter than the intended service interval.
Question 3: A maintenance team is troubleshooting a hydraulic cylinder that drifts under load. Oil analysis shows the fluid is clean and within viscosity specification. What lubrication-related cause should be ruled out next?
- Excessive fluid viscosity causing pressure drop
- Cylinder seal wear allowing internal bypass between piston faces (Correct answer)
- Incorrect ISO VG grade in the reservoir
- Oxidation degrading the fluid's shear stability
Correct answer: Cylinder seal wear allowing internal bypass between piston faces
A drifting hydraulic cylinder with acceptable fluid condition points to internal seal bypass, allowing fluid to pass from the high-pressure side to the low-pressure side of the piston.
Question 4: A plant is considering extending oil drain intervals in its diesel-powered lift trucks from 250 hours to 500 hours. Which approach best supports this decision?
- Simply adopting the OEM's maximum drain interval published in the manual
- Using used oil analysis (UOA) data over multiple samples to validate oil condition at 500 hours (Correct answer)
- Switching to a higher-viscosity engine oil that stays cleaner longer
- Running the trucks at lower loads to reduce oil degradation
Correct answer: Using used oil analysis (UOA) data over multiple samples to validate oil condition at 500 hours
Used oil analysis over multiple drain cycles provides empirical evidence of remaining oil life, making the drain interval extension scientifically defensible.
Question 5: After a bearing failure, inspection reveals a fluted (washboard) pattern on the outer race. Which root cause does this pattern indicate?
- Misalignment causing uneven load distribution across the race
- Electrical current passing through the bearing and creating arc damage (Correct answer)
- Over-greasing forcing grease against the cage
- Brinelling from an impact load during installation
Correct answer: Electrical current passing through the bearing and creating arc damage
Fluting on bearing races is the classic signature of electrical current discharge (EDM), which occurs when stray current arcs through the bearing contact zone.
Question 6: A lube engineer wants to reduce the number of lubricant SKUs in a plant from 87 to under 30. Which step is most important before consolidating products?
- Order the cheapest available lubricant in bulk to replace all others
- Map every lubrication point to its OEM requirements and operating conditions before selecting consolidated products (Correct answer)
- Remove all specialty lubricants first and replace with a single multi-purpose grease
- Consult only the lubricant supplier's catalog without reviewing equipment manuals
Correct answer: Map every lubrication point to its OEM requirements and operating conditions before selecting consolidated products
Consolidation must start with a full lubrication point inventory mapped against OEM requirements to ensure no equipment is left with an incompatible or under-performing lubricant.
Question 7: A steam turbine oil (ISO VG 46, R&O type) shows a ruler oxidation test value of 2.0 mg KOH/g after 18 months in service. The OEM condemns the oil at 2.0 mg KOH/g. What should the lube engineer do?
- Continue operating and retest in 6 months to confirm the trend
- Schedule an oil change promptly and investigate the cause of accelerated oxidation (Correct answer)
- Add an antioxidant top-treat to lower the acid number in situ
- Dilute the degraded oil with 10% fresh oil to reduce the acid number
Correct answer: Schedule an oil change promptly and investigate the cause of accelerated oxidation
An oil that has reached the OEM condemn limit should be changed promptly, and the root cause of rapid oxidation (heat, aeration, contamination) should be identified and corrected.
CLS Case Analysis & Practical Application 3
A lube tech is sampling oil from a turbine that operates at 65°C.
The sample is taken when the unit is shut down and the oil temperature has dropped to 25°C.
What is the main concern with this sampling approach?