ISO 24616:2020 Crane Hydraulic Systems Standard Interpretation
ISO 24616:2020, "Cranes — Hydraulic systems — Design principles and safety requirements," is the comprehensive standard governing crane hydraulic systems. It defines design principles, safety requirements, component selection criteria, and test methods for hydraulic systems across the full life cycle of mobile cranes, tower cranes, and industrial cranes.
Hydraulic System Design Principles
ISO 24616:2020 establishes the following design principles for crane hydraulic systems: Safety-first principle — The system must be designed to prevent loss of control (such as free-fall of the suspended load or uncontrolled boom lowering) under any failure mode, including hydraulic pump failure, hose rupture, or power supply interruption. Intrinsic safety principle — Mechanical safety devices that operate independently of external power and electronic controls (e.g., hydraulic lock valves, counterbalance valves) are preferred, and safety circuits must incorporate redundant design (dual circuits or parallel safety valves).
Fail-safe principle — In the event of a system failure, the equipment must automatically revert to a safe state or remain in its current safe position (e.g., a counterbalance valve automatically locks the hydraulic cylinder when control pressure is lost). Maintainability principle — Hydraulic components must be positioned for easy access during inspection and repair; hydraulic pipelines must include pressure test ports and vent valves; and the hydraulic oil tank must be equipped with an oil level gauge, oil temperature gauge, and magnetic filter. The standard also requires that the rated working pressure of the hydraulic system not exceed 85% of the hydraulic pump's rated pressure, and that continuous working pressure remain at or below 70% of that rating.
Safety Valves and Locking Devices
The standard specifies the following requirements for safety protection components in hydraulic systems: Counterbalance valves — Must be installed on hoisting and luffing hydraulic cylinders, with a set pressure of 1.3 to 1.5 times the load-induced pressure. The counterbalance valve must be mounted directly on the cylinder (not connected via hydraulic hose), ensuring the load remains locked even if a hose ruptures. Hydraulic lock valves — Double-acting hydraulic lock valves are mandatory on outrigger cylinders to prevent unintended retraction during lifting operations. The set pressure of the hydraulic lock valve must be at least 1.25 times the system's rated pressure.
Relief valves — A relief valve must be installed at the outlet of each hydraulic pump, with a set pressure not exceeding 1.1 times the system's rated pressure. Burst hose protection valves — These must be fitted on both the supply and return lines of hoisting motors and hydraulic cylinders, and must close automatically when flow exceeds 1.5 times the rated value. The standard also requires that all safety valves be equipped with sealing or locking features to prevent operators from adjusting set values without authorization.
| Safety components | installation position | Setpoint | Mode of operation | redundancyrequirements |
|---|---|---|---|---|
| counterbalance valve | Hoisting / Lifting/Luffing Cylinder | 1.3~1.5Load multiple | Pilot oil pressure release lock | Independent per cylinder |
| hydraulic lock valve | Outrigger Cylinder | ≥1.25Rated multiple | Dual pilot-operated Check Valve | Double-acting lock |
| Relief Valve | Hydraulic Pump Outlet | ≤1.1Rated multiple | Pilot-operated/Direct-acting | Per pump1pcs |
| Rupture valve | Motor/Cylinder line | ≥1.5Flow multiple | Flow-triggered shutoff | Critical circuit |
| Anti-cavitation valve | Hydraulic Cylinder Bottom | Vacuum-opening | Replenishing anti-cavitation | —— |
Filtration and Contamination Control
The standard sets clear requirements for filtration and contamination control in hydraulic systems. For filtration accuracy of hydraulic oil, the hoisting mechanism's hydraulic system must achieve a cleanliness level of NAS 8 or better (ISO 4406 18/15/13), while general hydraulic systems must meet NAS 9. Regarding filter configuration, return-line filters must have a filtration rating of ≤10 μm, high-pressure pipeline filters ≤5 μm (≤3 μm for servo valve systems), and suction-line filters ≤100 μm. Filters must be equipped with bypass valves and clogging indicators that signal or alarm when the differential pressure exceeds the set point.
For hydraulic oil performance and replacement intervals, anti-wear hydraulic oil (HM type) or low-temperature hydraulic oil (HV type) should be selected. Viscosity grade is determined by ambient temperature: VG46 is recommended for -20°C to +40°C, VG32 for -30°C to +30°C, and VG68 for 0°C to +50°C. Under normal operating conditions, hydraulic oil should be replaced every 2,000 hours or annually; in harsh environments, the interval is shortened to 1,000 hours. When changing oil, the tank and pipelines must be thoroughly flushed, and new oil should be filtered to NAS 7 before filling. For oil temperature control, the optimal operating range is 30–55°C; if the temperature exceeds 65°C, the machine should be stopped and the cooling system inspected.
Test Methods and Inspection Requirements
The hydraulic system tests specified by the standard include leak testing, dielectric test, functional test, and efficiency test. Leak testing — hold the system at 1.25 times the rated working pressure for 10 minutes and check all static seals for leakage. Dielectric test — hold the system at 1.5 times the rated working pressure for 3 minutes and check for permanent deformation or structural failure. Functional test — verify the smoothness, response speed, and limit positions of each mechanism's operation: hoisting/lifting at least 5 cycles, slewing at least 3 full rotations in both directions, and luffing through the full stroke at least 3 times.
All Kelude crane hydraulic systems undergo the complete battery of tests per ISO 24616:2020 before delivery, with test records archived for traceability. Hydraulic system assembly is carried out in a controlled-cleanliness workshop environment rated at Class 10,000. Hydraulic pipelines are flushed to NAS 7 cleanliness, and hydraulic components are verified with particle counters before assembly. The systems use imported seals and pipeline joints, effectively minimizing leakage rates.
| Test Item | test conditions | acceptance criteria | Inspection Type |
|---|---|---|---|
| Sealing Performance Test | 1.25Pressure multiple×10min | Leak-free | factory Full inspection |
| dielectric test | 1.5Pressure multiple×3min | Nonepermanent deformation | Type Test |
| functional test | Allstroke×3~5times | Smooth operation | factory Full inspection |
| Cleanliness Detection | Particle counter | NAS (Australian Standard)≤8Class | factory Full inspection |
| Efficiency Test | rated conditions Testing | System efficiency≥80% | Type Test |
FAQ
Q: What are the core design principles for a crane hydraulic system?
A: Safety first — no failure mode may result in uncontrolled load movement. Intrinsic safety — prioritize mechanical safety devices. Fail-safe design — the system defaults to a safe state upon failure. Serviceability — components are arranged for easy inspection and maintenance.
Q: Why must the counterbalance valve be mounted directly on the hydraulic cylinder?
A: Mounting the counterbalance valve directly on the hydraulic cylinder eliminates the risk of load loss due to a ruptured hose. If the valve is connected via hoses, a line failure can render it ineffective, potentially allowing the load to free-fall. Direct mounting is the most reliable safety configuration.
Q: How is the filtration accuracy of the hydraulic system determined?
A: The hoisting mechanism requires a cleanliness level of NAS 8 or better (ISO 4406 18/15/13), while general systems require NAS 9 or better. Return-line filters are rated at ≤10 μm, and high-pressure line filters at ≤5 μm. Insufficient filtration accelerates component wear. Kelude hydraulic systems come standard with high-pressure line filters.
Q: What should be done if the hydraulic oil temperature exceeds 65°C?
A: Shut down immediately and inspect the cooling system (radiator, cooling fan, and oil lines for blockages), check the hydraulic pump for excessive internal leakage, and verify the ambient temperature. Restart only after the fault is resolved and the oil temperature returns to normal. Prolonged high temperatures accelerate oil oxidation and degradation.
