Analysis of the reasons why deck crane booms can be lowered but not raised

Deck cranes play a crucial role in offshore operations; however, when their booms malfunction and cannot be raised, it severely impacts work efficiency and safety. A crane boom's inability to rise is typically caused by hydraulic system failure, control valve problems, or damage to mechanical components. The specific causes are analyzed below:

I. Hydraulic System Failure

The hydraulic system is the core power source for the boom lifting and lowering of the crane. If the hydraulic system malfunctions, the boom may fail to lift properly. Specifically, damage to the hydraulic pump, hydraulic valves, or hydraulic cylinders can all cause this problem. Furthermore, leaks or contamination of the hydraulic oil can also affect the normal operation of the hydraulic system, leading to obstructed boom lifting and lowering. Common problems include:

1. Clogged Relief Valve or Damper: Clogged damper at end A of the relief valve in the lifting circuit can cause poor oil flow, preventing the boom from obtaining sufficient pressure to rise.

2. Sticking or Clogged Solenoid Valve: A stuck solenoid valve in the multi-way directional valve due to impurities can block the flow of hydraulic oil to the luffing motor, causing the boom to not move.

3. Insufficient Pump Pressure: Wear of the main pump or incorrect safety valve settings can cause the system pressure to be lower than the lifting requirements, preventing the boom from being driven.

4.Contaminated Hydraulic Oil or Abnormal Oil Temperature: Poor oil cleanliness or excessively high oil temperature (e.g., exceeding 60°C) will reduce hydraulic efficiency and trigger a protective shutdown of the system.

II. Electrical Control Issues

The electrical control system is crucial for ensuring the accurate raising and lowering of the boom according to commands. Failures in the electrical control system, such as sensor malfunction, damaged control wiring, or faulty electronic valves, can prevent the boom from receiving or executing raising commands. Common problems include:

1. Luffing Unit Control Valve Failure: If the internal spring of the control valve breaks, the luffing function will be completely lost, and the boom will be unable to raise or lower.

2. Hydraulic Motor Damage: Mechanical damage such as a broken return disc or a broken distributor plate inside the luffing hydraulic motor will cause power output interruption.

3. Braking System Failure: Worn brake pads or a faulty brake solenoid valve spool can cause the boom to lose its position under load, indirectly affecting the raising action.

III. Damage to Mechanical Components The raising and lowering of the boom relies on a series of mechanical components, such as wire ropes, pulleys, and bearings. The condition and maintenance level of these components directly affect reliability, and damage or wear of these components can prevent the boom from raising properly. Common problems include:

1. Broken wire ropes or stuck bearings directly affect the boom's raising and lowering function.

2. Insufficient lubrication: Blocked grease channels or lack of lubrication in the boom bearings increase operating resistance and may even lead to dry friction and seizure.

3. Excessive wear of components: Failure to replace broken wire rope strands or stuck pulleys in a timely manner will restrict boom movement.

4. Improper operation: Dockworkers unfamiliar with the equipment or engaging in excessive operation may trigger safety locks, preventing the boom from responding to commands.

When encountering such malfunctions, these potential factors should be investigated one by one in order to accurately find the cause of the malfunction and repair it in a timely manner, so as to ensure the normal operation of the crane and the safe and efficient conduct of offshore operations.