WTT Hydraulic & Lubrication Systems 3 — Questions and Answers
Question 1: What is the function of a pressure relief valve in a hydraulic circuit?
- To increase system flow rate
- To protect the system from overpressure by diverting excess fluid to tank (Correct answer)
- To maintain minimum pressure during low-load operation
- To filter particulate contamination from the fluid
Correct answer: To protect the system from overpressure by diverting excess fluid to tank
A pressure relief valve opens when system pressure exceeds a set limit, diverting fluid to tank to prevent component damage.
Question 2: A gearbox oil sample analysis shows elevated iron (Fe) and copper (Cu) particles. What does this most likely indicate?
- Normal wear within acceptable limits
- Contamination from the hydraulic system
- Wear in steel gear surfaces and bronze bushings or thrust washers (Correct answer)
- Water ingress from the cooler
Correct answer: Wear in steel gear surfaces and bronze bushings or thrust washers
Elevated iron indicates steel gear or bearing wear, while copper particles point to bronze bushing or thrust washer degradation.
Question 3: What is the recommended method for transferring lubricating oil into a wind turbine gearbox to minimize contamination?
- Pour directly from the drum using a funnel
- Use a dedicated transfer pump with a 10-micron or finer filter (Correct answer)
- Transfer at maximum ambient temperature only
- Mix new oil with old oil to reduce cost
Correct answer: Use a dedicated transfer pump with a 10-micron or finer filter
Using a dedicated transfer pump with fine filtration prevents particulate contamination that can accelerate gear and bearing wear.
Question 4: Which parameter is most critical when selecting grease for wind turbine pitch and yaw bearing lubrication?
- Color of the grease
- NLGI grade and base oil viscosity appropriate for low temperature and high load (Correct answer)
- Flash point above 200°C
- Water washout resistance only
Correct answer: NLGI grade and base oil viscosity appropriate for low temperature and high load
NLGI grade and base oil viscosity determine pumpability at low temperatures and film strength under the high loads of pitch and yaw bearings.
Question 5: What is the purpose of a hydraulic flow divider in a multi-actuator pitch system?
- To increase total system pressure
- To ensure equal flow to each pitch cylinder for synchronized blade movement (Correct answer)
- To reduce pump speed under light load
- To filter the hydraulic fluid before it reaches cylinders
Correct answer: To ensure equal flow to each pitch cylinder for synchronized blade movement
A flow divider splits hydraulic flow equally among multiple cylinders, ensuring all three blades pitch simultaneously and uniformly.
Question 6: At what water content level (ppm) does water in hydraulic oil typically begin to cause significant bearing damage through hydrogen embrittlement?
- Greater than 5,000 ppm
- Greater than 500 ppm (Correct answer)
- Greater than 50,000 ppm
- Any detectable water above 0 ppm
Correct answer: Greater than 500 ppm
Water concentrations above approximately 500 ppm promote hydrogen embrittlement and accelerated fatigue in hardened bearing steel.
Question 7: A hydraulic directional control valve fails to shift when energized. After confirming electrical power is present at the solenoid, what is the next diagnostic step?
- Replace the entire hydraulic power unit
- Check for mechanical spool binding, contamination, or insufficient pilot pressure (Correct answer)
- Increase system relief valve setting by 50 bar
- Drain and refill the reservoir immediately
Correct answer: Check for mechanical spool binding, contamination, or insufficient pilot pressure
If the solenoid has power but the valve won't shift, a mechanically stuck spool, contamination, or low pilot pressure is the likely cause.
WTT Hydraulic & Lubrication Systems 3
What is the function of a pressure relief valve in a hydraulic circuit?