CMRT Troubleshooting and Analysis Questions and Answers — Questions and Answers
Question 1: A technician is investigating a recurring failure on a hydraulic power unit. After fixing the immediate symptom (a blown fuse), they use the '5 Whys' technique to find the root cause. The analysis proceeds as follows: 1. Why did the fuse blow? - The motor overloaded. 2. Why did the motor overload? - The pump was working too hard. 3. Why was the pump working too hard? - The fluid was too thick (viscosity too high). What is the MOST logical fourth 'Why' question to ask in this analysis?
- Why was the system pressure so high?
- Why was the incorrect fluid used or why has the fluid degraded? (Correct answer)
- Why did the motor's thermal overload not trip first?
- Why was the pump shaft worn out?
Correct answer: Why was the incorrect fluid used or why has the fluid degraded?
The 5 Whys technique is a sequential questioning process used to explore the cause-and-effect relationships underlying a problem. [3, 19] Each answer forms the basis for the next question. Since the third answer identified that the fluid viscosity was too high, the next logical step is to question why the fluid is in that state. This could be due to contamination, thermal breakdown, or simply using the wrong type of oil, which directly addresses the previous answer. [3, 18, 19]
Question 2: A team is conducting a Failure Modes and Effects Analysis (FMEA) on a critical piece of equipment. What is the primary goal of this type of analysis?
- To reactively document failures after they have occurred.
- To prioritize maintenance work orders based on cost.
- To proactively identify potential failure modes and their consequences. (Correct answer)
- To calculate the mean time between failures (MTBF) for the asset.
Correct answer: To proactively identify potential failure modes and their consequences.
Failure Modes and Effects Analysis (FMEA) is a systematic and proactive method for identifying potential failures *before* they occur. [15, 27, 36] The core purpose is to analyze the ways a system or component can fail (failure modes) and the potential impact of those failures (effects) to implement preventative actions and mitigate risks. [2, 33]
Question 3: When troubleshooting a pneumatic actuator that is moving too slowly, a technician has confirmed that the air pressure supplied to the directional control valve is correct. Which of the following is the MOST likely cause of the slow movement?
- The compressor is overheating.
- The FRL (Filter, Regulator, Lubricator) unit has been removed.
- The cylinder piston seals are completely blown.
- A flow control valve is incorrectly adjusted or an exhaust silencer is clogged. (Correct answer)
Correct answer: A flow control valve is incorrectly adjusted or an exhaust silencer is clogged.
If the pressure is adequate at the control valve, the issue is likely downstream, affecting the volume of air that can enter or exit the actuator. A flow control valve that is too restrictive or a clogged exhaust silencer (muffler) will limit the speed at which air can be vented, thereby slowing the actuator's movement. [14, 17] While completely blown seals could cause slow movement, it often results in no movement or drifting, and a clogged exhaust is a very common cause of this specific symptom.
Question 4: A maintenance team is using a Fishbone (Ishikawa) diagram to analyze the root cause of frequent bearing failures on a fan. Which of the following would be an appropriate category, or 'bone,' to use on this diagram?
- Return on Investment
- Predictive Maintenance Schedule
- Methods (Correct answer)
- Failure Code
Correct answer: Methods
The Fishbone diagram, also known as an Ishikawa or cause-and-effect diagram, organizes potential causes into categories to identify the root cause of a problem. [6, 7] Standard categories often used in manufacturing and maintenance are the 6Ms: Manpower, Methods, Machines, Materials, Measurement, and Mother Nature (Environment). [6] 'Methods' refers to the procedures and processes used, such as lubrication procedures or installation techniques, which is a key area to investigate for bearing failures.
Question 5: A technician reviews an oil analysis report for a gearbox that shows a sudden, significant increase in the iron (Fe) and copper (Cu) particle count, while silicon (Si) levels remain normal. What is the MOST likely interpretation of these results?
- The gearbox is contaminated with dirt and sand from the environment.
- The wrong type of lubricant was added during a top-off.
- There is accelerated wear of internal steel gears and bronze bushings. (Correct answer)
- The oil has exceeded its useful life due to oxidation.
Correct answer: There is accelerated wear of internal steel gears and bronze bushings.
Oil analysis reports identify wear metals from specific components. Iron (Fe) is the primary element in steel, used for gears and shafts. Copper (Cu) is a primary element in bronze or brass, often used for bushings, thrust washers, or bearing cages. [31, 32] A simultaneous spike in both indicates accelerated wear of these specific internal components. Normal silicon (Si) levels suggest that external contamination like dirt (silica) is not the cause. [32]
Question 6: During troubleshooting of a hydraulic system that is operating erratically, the technician notices the hydraulic fluid in the reservoir appears milky or foamy. This is a primary indicator of what type of contamination?
- Varnish and sludge buildup
- Excessive particulate matter
- Air or water entrainment (Correct answer)
- Cross-contamination with gear oil
Correct answer: Air or water entrainment
Milky or foamy-looking hydraulic fluid is a classic symptom of either air or water contamination. [23] Air entering the system (aeration) can cause foaming, while water contamination (emulsification) gives the oil a milky appearance. Both conditions degrade lubricant properties and can cause erratic operation and damage to components like pumps. [4, 23]
CMRT Troubleshooting and Analysis Questions and Answers
A technician is investigating a recurring failure on a hydraulic power unit.
After fixing the immediate symptom (a blown fuse), they use the '5 Whys' technique to find the root cause.
The analysis proceeds as follows: 1.
Why did the fuse blow? - The motor overloaded. 2.
Why did the motor overload? - The pump was working too hard. 3.
Why was the pump working too hard? - The fluid was too thick (viscosity too high).
What is the MOST logical fourth 'Why' question to ask in this analysis?