Maintenance and Troubleshooting Flashcards

During a load test on a hydraulic telescoping boom crane, the boom extends normally but retracts sluggishly even under no-load conditions. The hydraulic oil level is correct and the pump pressure reads within specification. Which component is MOST likely causing this condition?

Answer: A worn counterbalance valve on the retract circuit holding pressure too long

A counterbalance valve on the retract circuit that is worn or sticking will hold back-pressure longer than necessary, causing sluggish retraction even with correct system pressure and oil level. A clogged case drain would affect motor function, not cylinder speed. A low retract relief valve would allow retraction but with loss of force under load, not sluggishness at no load. Air entrapment on the extend side would cause spongy extension, not slow retraction.

A lattice boom crawler crane passes its pre-shift inspection but during operation the operator notices the load line sheave on the boom tip is running hot after only 30 minutes of use. The sheave rotates freely by hand with the crane shut down. What is the MOST probable cause?

Answer: A worn sheave groove that no longer matches the rope diameter

A worn sheave groove that has become undersized or mismatched to the rope diameter causes the rope to ride on the groove flanks rather than the groove base, generating friction and heat during operation — yet the sheave still spins freely when the rope tension is removed during shutdown inspection. Insufficient lubrication typically causes noise and binding detectable by hand. Rope rubbing a guard would produce visible wear marks. Overtensioned rope would show other symptoms such as difficulty spooling.

A mobile crane's load moment indicator (LMI) is showing a rated capacity that is 12% higher than the capacity chart for the current configuration. The boom angle sensor and radius readout appear correct. Which troubleshooting step should be performed FIRST before operating the crane?

Answer: Verify that the correct crane configuration (outrigger span, boom type, counterweight) is programmed into the LMI

An LMI displaying inflated capacity is most commonly caused by an incorrect configuration being programmed — for example, a wider outrigger span or heavier counterweight setting than what is actually installed. This would cause the system to reference a more favorable chart, inflating displayed capacity while the angle and radius appear correct. Operating on the inflated capacity could exceed the actual crane rating. Overriding the LMI is never appropriate. Replacing the transducer or recalibrating the angle sensor would not address a configuration mismatch.

While inspecting wire rope on a crane that has been in cold-weather storage, a rigger finds that the rope appears stiff and the fiber core shows evidence of moisture. The outer wires show no corrosion or broken wires. What is the correct course of action according to ASME B30.2 maintenance principles?

Answer: Remove the rope from service; a moisture-damaged fiber core compromises the rope's rated capacity regardless of outer wire condition

ASME B30.2 and industry standards require removal from service of wire rope with a deteriorated fiber core. The fiber core provides internal lubrication and support for the outer strands; moisture damage (especially freeze-thaw cycling) causes internal corrosion, fiber breakdown, and loss of the core's structural contribution, which reduces the rope's rated capacity even if the outer wires appear intact. Lubricating and continuing use ignores the internal degradation. Downrating is not a recognized field remedy for core damage.

A tower crane operator reports that the trolley travel limit switch activates correctly at the outer end but the inner (minimum radius) travel limit is not stopping the trolley. The limit switch assembly checks out electrically with continuity confirmed. What is the MOST likely cause of the inner limit failing to stop trolley travel?

Answer: The cam or striker on the trolley has shifted out of alignment with the inner limit switch actuator

Trolley travel limits on tower cranes rely on a physical cam or striker mounted on the trolley contacting a fixed switch actuator at specific positions. If the cam shifts (due to loose fasteners, collision, or maintenance work), the outer limit position may still function if that cam remained aligned, while the inner limit cam no longer contacts its actuator — producing exactly this asymmetric failure. Electrical continuity confirms the switch itself works, pointing to a mechanical actuation problem. Wiring configurations and brake drag would typically affect both limits or present differently.

During annual wire rope inspection on a crane using rotation-resistant rope, an inspector finds that the rope has lengthened by approximately 2% of its working length compared to the manufacturer's original specification, with no measurable diameter reduction and no broken wires. What does this condition MOST likely indicate?

Answer: Core failure or birdcaging precursor — the rope should be removed from service

In rotation-resistant multi-layer rope, lengthening without diameter reduction and without broken outer wires is a classic indicator of internal core failure or strand unlaying — the outer strands are redistributing load as the inner structure loses integrity. This is particularly dangerous because the failure is not externally visible. Normal break-in stretch in rotation-resistant rope is much smaller (typically under 0.5%) and occurs early in service life. Permanent overload stretch would typically be accompanied by diameter reduction. This condition is an ASME B30.2 removal criterion.