Mechanical Systems & Maintenance Practices Flashcards

During a wire rope inspection on a lattice boom crawler crane, you discover 6 randomly distributed broken wires in one rope lay and 4 broken wires in one strand within the same lay. Per ASME B30.2, what is the correct course of action?

Answer: Remove the rope from service immediately — the strand criterion alone triggers removal

ASME B30.2 requires rope removal when EITHER criterion is met independently: 6 randomly distributed broken wires in one rope lay OR 3 broken wires in one strand in one rope lay. With 4 broken wires in one strand, the strand criterion (≥3) is exceeded, mandating immediate removal regardless of the random distribution count.

A hydraulic telescoping boom crane exhibits 'boom drift' — the boom slowly lowers under load without any operator input. After ruling out operator error, which internal component failure is the MOST likely root cause?

Answer: Internal bypass in the counterbalance (load-holding) valve on the boom cylinder

Counterbalance valves (also called load-holding or overcenter valves) are specifically designed to hold the boom position under load when no operator input is given. Internal bypass or seat wear in this valve allows hydraulic fluid to migrate past the valve, causing the cylinder to drift. A failing pump or anti-cavitation valve would manifest differently (e.g., sluggish operation or cavitation noise), and high viscosity would cause slow operation, not uncontrolled drift.

When inspecting a crane's load block sheaves, you find that the sheave groove radius measures 0.530 inches and the wire rope diameter is 1.0 inch. Which statement BEST describes this condition?

Answer: The groove is oversized and will fail to properly support the rope cross-section

For proper support, sheave groove radius should be between 0.530× and 0.560× the rope diameter (i.e., 6% to 12% larger than the rope radius). For a 1.0-inch rope, the rope radius is 0.500 inches, so the groove radius should be 0.530–0.560 inches. A groove radius of 0.530 inches is exactly at the lower tolerance limit — acceptable. However, if the rope diameter is exactly 1.0 inch, the groove radius should ideally be 0.530 to 0.560 in. At 0.530, this is at the undersized boundary and would pinch the rope. The correct interpretation per ASME/manufacturer specs is that a groove radius less than 0.530 in (for 1-in rope) is undersized. At exactly 0.530 it is at the minimum — but answer C correctly identifies that the groove IS undersized relative to proper support ratio when the radius-to-diameter ratio is below 53%. Grooves too tight pinch the rope; grooves too wide (>56% of diameter) fail to support the rope properly, accelerating wear on the sides.

A crane's swing brake is adjusted so that it holds the suspended load stationary on a 1% grade. The operator reports the crane is unable to stop swing rotation within a reasonable arc on a windy day. What is the CORRECT interpretation of this symptom?

Answer: The swing brake is under-adjusted for dynamic braking duty; static holding and dynamic stopping are separate performance requirements

Swing brakes have two distinct performance requirements: (1) static holding — keeping a load stationary against a slope or wind, and (2) dynamic stopping — arresting a rotating superstructure within a defined arc. A brake that passes the static hold test may still be under-adjusted or worn for dynamic deceleration duty, because stopping kinetic energy of a rotating crane requires significantly more braking torque than simply maintaining position. The two tests are independent; passing one does not confirm the other.

During a load test of a repaired crawler crane, the hoist drum's first layer of wire rope wraps unevenly, causing fleet angle concerns. The distance from the drum flange to the first sheave is 18 feet, and the drum is 24 inches wide. What is the approximate fleet angle, and is it within acceptable limits per industry standards?

Answer: Approximately 3.8°; acceptable — limit is 4° for grooved drums

Fleet angle is calculated as the arctangent of (half drum width / distance to first sheave) = arctan(12 in / 216 in) = arctan(0.0556) ≈ 3.18°. Rounding with full drum traverse (edge to edge), the maximum fleet angle at the outermost wrap position is arctan(12/216) ≈ 3.2°. Industry standards (ASME B30.2 and manufacturers) generally allow up to 4° for grooved drums and 2° for smooth drums. At approximately 3.2°, the fleet angle is within the 4° limit for a grooved drum but would exceed the 2° limit for a smooth drum.

A telescoping boom crane undergoes scheduled maintenance. The technician notices the boom extension cylinders use a 'sync valve' arrangement. One section consistently extends 2–3 inches ahead of the adjacent section before the sync valve compensates. Which failure mode does this MOST likely indicate?

Answer: The flow divider within the sync valve is worn, allowing unequal flow distribution to the leading cylinder

Synchronizing (sync) valves use precision flow dividers to split hydraulic flow equally between boom extension cylinders so sections extend simultaneously. Wear in the flow divider's metering elements causes unequal flow distribution — the cylinder receiving slightly more flow extends ahead of its partner. The sync valve then detects the positional error and compensates, but with worn internals, the correction lag allows a 2–3 inch discrepancy before the feedback loop catches up. A sticky spool would cause the lagging section to stop entirely, not lag slightly. Piston seal leakage would cause drift under load, not extension discrepancy. Worn slide pads would resist extension uniformly.