Mobile Crane Outrigger Leveling & Torque Limiter Training
GB/T 23720.2-2009 "Cranes — Operator Training — Part 2: Mobile Cranes" is the dedicated standard for training mobile crane operators. Building on the general principles in Part 1, it defines the training content and assessment requirements for the specific skills unique to mobile crane operation — outrigger leveling, load capacity chart interpretation, boom control, and load moment limiter (LML) operation.
GB/T 23720.2-2009 is Part 2 of the crane operator training standard series, specifically addressing the training requirements for mobile crane operators in outrigger leveling and load moment limiter operation. Proper outrigger handling and correct use of the load moment limiter are critical to safe mobile crane operation. This article breaks down the core requirements of the standard.
Standard Scope and Training Characteristics
GB/T 23720.2-2009 is identical to ISO 9926-2:2004 (IDT) and focuses specifically on the training of mobile crane operators. Compared with overhead and gantry crane operation, mobile crane operator training covers several unique areas: Load capacity chart reading and application — the rated lifting capacity of a mobile crane varies significantly with outrigger configuration, jib length, working radius, and slewing angle, so operators must be thoroughly proficient in using the load capacity chart. Outrigger operation — capacity limitations for fully extended, partially extended, and retracted outrigger positions, plus outrigger leveling procedures. Boom telescoping and luffing — sequenced boom extension (correct order and synchronization of individual boom sections) and load behavior during luffing. Understanding the load moment limiter (LML) — how the LML works, interpreting display readings, and proper response to alarms.
Theoretical Training Content
The theoretical portion of mobile crane operator training covers: Crane construction — structural features of truck cranes, crawler cranes, and all-terrain cranes; the working principles of each system (hoisting, slewing, luffing, telescoping, and traveling); and fundamentals of the hydraulic drive system. Load capacity chart interpretation — the relationship between outrigger configuration and lifting capacity, the effect of working radius on rated lifting capacity, the effect of jib length changes on rated lifting capacity, and the safety factor implications built into the chart. Basic mechanics — the concept of torque (torque = force × lever arm), the effect of center of gravity position on stability, and how lifting point selection and sling angle affect sling tension (tension increases as the included angle widens). Safety regulations — the safety operating procedures specified in GB/T 23723.2, the Ten No-Lift Rules, outrigger safety rules, and safe clearance distances from high-voltage lines. Accident case studies — common causes and lessons learned from overload overturning, outrigger settlement, boom buckling, and high-voltage line contact incidents.
Practical Training Content
Practical training for mobile crane operators should include the following skill drills: Outrigger operation — extending and leveling outriggers on both firm, level ground and soft ground, using a spirit level (bubble or electronic) to confirm crane levelness within 0.5°. No-load operation — practicing basic maneuvers with no load: hoisting and lowering (controlling hook positioning accuracy within 100 mm), slewing (smooth starts and stops with 90° and 180° positioning), and boom telescoping (extending and retracting sections sequentially and in synchronization). Loaded operation — lifting 50%, 75%, and 100% of rated load at various jib lengths and working radii: sensing the crane's stability changes under different loads and practicing smooth lifts at maximum radius. Complex conditions — lifting operations in confined spaces with obstacles, simulated lifting scenarios (e.g., structural member alignment and placement), and practicing emergency stops and fault response during lifts.
Assessment Criteria
Assessment of mobile crane operators consists of both theoretical and practical components. Theoretical examination: a written (or computer-based) test covering mobile crane structure and principles, load capacity chart interpretation, safety regulations, and accident case analysis. The test is scored out of 100, with a passing mark of 80. Practical assessment: conducted on an actual mobile crane, covering — outrigger leveling (to be completed within 5 minutes, levelness within 0.5°), bucket-around-obstacles (hoisting a water-filled bucket along a prescribed path around obstacles without touching them or spilling water), precision placement (positioning the load within 100 mm of the target), and emergency operation (correct response to a simulated limit switch activation or LML alarm). The practical assessment is scored by at least two examiners. Upon passing, candidates are issued a Special Equipment Operator Certificate (Q2 — Mobile Crane Operator).
Mobile Crane Operator Training Comparison Table
The comparison table below outlines the core parameters and configurations for mobile crane operator training, for reference by those involved in equipment selection and crane operation.
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| training module | training content | Skillrequirements | assessment method |
|---|---|---|---|
| Outrigger Operation | Ground Assessment/Outrigger Deployment/Leveling | Levelness≤0.5Degree | practical assessment |
| Load moment limiter (LML) | Principle/Setpoint/Alarm Handling | Correct Instrument Reading | Written Test+Practical Test |
| lifting capability table | Lifting Capacity/Working radius/jib length Relationship | Proficient Table Lookup and Calculation | Written Testassessment |
| safe operation | Prohibitionoverload/wind speed limit/Anti-overturning protection | safe operation Awareness | Comprehensive Evaluation |
