NCCCO Mechanical Systems & Maintenance Practices 5 — Questions and Answers
Question 1: What condition in a hydraulic system is indicated by a whining or cavitation noise from the pump, especially at startup?
- Excessive system pressure
- Fluid starvation or aeration at the pump inlet (Correct answer)
- Faulty pressure relief valve
- Worn hydraulic motor seals
Correct answer: Fluid starvation or aeration at the pump inlet
Cavitation noise at the pump occurs when the inlet is starved of fluid or air enters the suction line, causing vapor bubbles to collapse inside the pump.
Question 2: During a pre-shift inspection, an operator notices the crane's boom hoist pawl (ratchet) is worn and not engaging properly. What action is required?
- Note it in the log and continue operating
- Remove the crane from service immediately until repaired (Correct answer)
- Engage the pawl manually before each lift
- Lubricate the pawl and monitor it during the shift
Correct answer: Remove the crane from service immediately until repaired
A boom hoist pawl that fails to properly engage is a critical safety device defect that requires immediate removal from service until the component is repaired.
Question 3: What does a high differential reading between incoming and outgoing hydraulic filter pressure gauges indicate?
- Insufficient pump output
- A clogged or loaded hydraulic filter (Correct answer)
- High ambient temperature affecting fluid viscosity
- A partially open directional control valve
Correct answer: A clogged or loaded hydraulic filter
A high differential pressure across the filter indicates the filter element is loaded with contaminants and requires replacement before bypassing occurs.
Question 4: Which type of crane structural inspection involves checking for cracks, deformations, and corrosion on the boom chord members and lacings?
- Frequent inspection
- Periodic inspection (Correct answer)
- Initial inspection
- Daily walk-around inspection
Correct answer: Periodic inspection
Periodic inspections, typically performed by a qualified person at intervals specified by the manufacturer, include detailed structural examination of boom chord members and lacings.
Question 5: A crane's counterweight becomes partially detached during operations. What is the immediate required action?
- Reduce the load and complete the lift
- Stop all operations, lower the load if safe, and secure the crane (Correct answer)
- Slow the swing speed and monitor the counterweight
- Call a mechanic while keeping the load suspended
Correct answer: Stop all operations, lower the load if safe, and secure the crane
A detached counterweight is an immediate structural hazard; all operations must stop, the load lowered if safely possible, and the crane secured.
Question 6: What is the function of the crane's swing lock or travel lock when the crane is being transported or when not in use?
- Prevents the boom from lowering below horizontal
- Prevents uncontrolled rotation of the upperworks (Correct answer)
- Limits the maximum swing speed
- Disconnects the swing motor from the hydraulic circuit
Correct answer: Prevents uncontrolled rotation of the upperworks
The swing lock secures the upperworks against uncontrolled rotation during transport or when the crane is parked, preventing hazardous unexpected movement.
Question 7: When replacing wire rope on a hoist drum, what is the minimum number of wraps that must remain on the drum when the hook is at its lowest working position?
- 1 wrap
- 2 wraps (Correct answer)
- 3 wraps
- 5 wraps
Correct answer: 2 wraps
At least two wraps of wire rope must remain on the drum at all times to ensure the rope's anchor attachment point does not bear the load.
NCCCO Mechanical Systems & Maintenance Practices 5
What condition in a hydraulic system is indicated by a whining or cavitation noise from the pump, especially at startup?