ITMC Hydraulic Systems 4 — Questions and Answers
Question 1: What ISO cleanliness code reading of 18/16/13 means in a hydraulic system?
- Particle count levels per milliliter at 4, 6, and 14 micron size ranges (Correct answer)
- The fluid has been filtered three times to three different levels
- Temperature cycles the fluid has undergone
- Viscosity grade at three different temperatures
Correct answer: Particle count levels per milliliter at 4, 6, and 14 micron size ranges
Each ISO 4406 number represents a range of particle counts per milliliter at 4µm, 6µm, and 14µm respectively.
Question 2: A hydraulic motor stalls under load even though system pressure is adequate. What is the most likely cause?
- Excessive internal leakage within the motor (Correct answer)
- Low reservoir fluid level
- Stuck pressure relief valve in the open position
- Clogged return line filter
Correct answer: Excessive internal leakage within the motor
Worn motor components allow internal bypass of fluid, reducing torque output even when supply pressure is sufficient.
Question 3: Which hydraulic fitting connection type is least prone to leakage under high-pressure pulsating conditions?
- O-ring face seal (ORFS) (Correct answer)
- NPT threaded pipe fitting
- JIC 37-degree flare
- Compression fitting
Correct answer: O-ring face seal (ORFS)
ORFS fittings use an elastomeric O-ring on a flat face, providing a positive seal unaffected by pressure pulses.
Question 4: What does the term 'pump volumetric efficiency' measure?
- Actual flow output compared to theoretical flow based on displacement and speed (Correct answer)
- Ratio of output power to input power
- Percentage of fluid that remains clean after filtration
- Ratio of pump speed to maximum rated speed
Correct answer: Actual flow output compared to theoretical flow based on displacement and speed
Volumetric efficiency accounts for internal pump leakage; a new pump may be 95%+ efficient while a worn pump drops significantly.
Question 5: When troubleshooting a hydraulic system with no actuator movement, which component should typically be checked first?
- Fluid level and pump output (Correct answer)
- Directional control valve solenoid
- Cylinder piston seal condition
- System pressure setting
Correct answer: Fluid level and pump output
Confirm the pump is producing flow and pressure before suspecting downstream components in a no-movement diagnosis.
Question 6: What is the effect of increasing hydraulic fluid viscosity beyond the recommended range in cold weather?
- Increased pressure drop, sluggish operation, and possible pump cavitation (Correct answer)
- Faster actuator response due to reduced fluid slippage
- Improved sealing of worn clearances
- Lower operating temperatures due to reduced friction
Correct answer: Increased pressure drop, sluggish operation, and possible pump cavitation
Excessively viscous fluid resists flow, causing high pressure drops in lines, slow actuation, and pump starvation.
Question 7: A proportional hydraulic valve differs from a standard directional control valve in that it:
- Provides variable flow and direction control proportional to an electrical input signal (Correct answer)
- Only allows flow in one direction
- Operates exclusively by manual control
- Uses mechanical springs for all positioning
Correct answer: Provides variable flow and direction control proportional to an electrical input signal
Proportional valves use a variable-force solenoid to position the spool proportionally, enabling precise speed and direction control.
ITMC Hydraulic Systems 4
What ISO cleanliness code reading of 18/16/13 means in a hydraulic system?