ITMC Hydraulic Systems 5 — Questions and Answers
Question 1: What is the correct procedure when replacing a hydraulic hose assembly?
- Depressurize the system, tag out, replace with same spec hose, and check for leaks at operating pressure (Correct answer)
- Replace while system is running to avoid fluid spillage
- Use any available hose with adapters if exact spec is unavailable
- Tighten all fittings 25% beyond spec to prevent leaks
Correct answer: Depressurize the system, tag out, replace with same spec hose, and check for leaks at operating pressure
Safe hose replacement requires full system de-energization and exact specification replacement to maintain system integrity.
Question 2: In a hydrostatic transmission, the pump and motor are both variable displacement. What advantage does this provide?
- Infinite speed ratio adjustment and regenerative braking capability (Correct answer)
- Higher maximum pressure than gear systems
- Elimination of all hydraulic seals
- Constant output torque regardless of load
Correct answer: Infinite speed ratio adjustment and regenerative braking capability
Variable displacement on both sides allows smooth, stepless speed control and enables the motor to act as a pump for braking.
Question 3: A hydraulic system experiences pressure spikes that damage components. What device best protects against this?
- Nitrogen-charged bladder accumulator (Correct answer)
- Larger reservoir
- Higher-rated pressure relief valve
- Additional inline filter
Correct answer: Nitrogen-charged bladder accumulator
A bladder accumulator absorbs pressure spikes by compressing the pre-charged nitrogen gas when fluid pressure surges.
Question 4: What is the recommended method for detecting hydraulic system leaks in tight or hidden areas?
- UV fluorescent dye added to the fluid, inspected with a UV light (Correct answer)
- Increasing system pressure to 150% to force visible leaks
- Running the system dry to identify contamination sources
- Applying soapy water to all connections
Correct answer: UV fluorescent dye added to the fluid, inspected with a UV light
UV dye is injected into the system, and a UV lamp reveals even pinhole leaks that are otherwise invisible.
Question 5: Which condition causes thermal runaway in a hydraulic system?
- Heat generated by inefficiencies exceeds the system's cooling capacity, continuously raising fluid temperature (Correct answer)
- A stuck-open thermal bypass valve directing all flow through the cooler
- Fluid viscosity dropping below minimum, reducing friction heat
- Pump overspeeding during light-load conditions
Correct answer: Heat generated by inefficiencies exceeds the system's cooling capacity, continuously raising fluid temperature
When system inefficiencies (leakage, relief valve bypassing) generate more heat than the cooler can remove, temperatures rise uncontrollably.
Question 6: What is the primary difference between a hydraulic servo valve and a proportional valve?
- Servo valves use closed-loop feedback for higher precision; proportional valves typically use open-loop control (Correct answer)
- Servo valves operate at lower pressures than proportional valves
- Proportional valves require cleaner fluid than servo valves
- Servo valves can only control direction, not flow
Correct answer: Servo valves use closed-loop feedback for higher precision; proportional valves typically use open-loop control
Servo valves incorporate position feedback (LVDT) and achieve much tighter control accuracy than open-loop proportional valves.
Question 7: When pre-charging a bladder accumulator with nitrogen, the pre-charge pressure should typically be set to:
- 60–90% of minimum system working pressure (Correct answer)
- Equal to maximum system pressure
- 25% of maximum system pressure
- Equal to atmospheric pressure before installation
Correct answer: 60–90% of minimum system working pressure
Pre-charge at 60–90% of minimum working pressure ensures the bladder does not fully collapse or over-extend during operation.
ITMC Hydraulic Systems 5
What is the correct procedure when replacing a hydraulic hose assembly?