Greetings! Another problem occurred on the cargo crane; its jib is slowly going down without affecting the manipulator (joystick). More precisely, the crane boom is lowered down and stopped, but by inertia it continues to go down without operator action under its own weight.
This problem can lead to significant damage and therefore requires immediate elimination. In the previous article, we looked at a situation where the crane hook was slow to move (abnormal speed of the crane) when operating on the corresponding joystick.
At the same time, all the crane automation components that are involved in this operation were shown.
In this case, engineers attention was focused on the drum hydraulic motor and the luffing brake, which is affected by the solenoid. When a command is given to the luffing down, the solenoid receives power and the hydraulic motor is released.
The first step was to replace the connections for the brake solenoids. The hoses on the high speed and luffing solenoid blocks were swapped and the connections on the coils were changed accordingly.
This experiment did not give a positive result. The solenoid coils were checked in advance, but it was initially clear that this could not be a problem. Because if the coils burned out, the cargo crane would not work at all.
The next step was to check the hydraulic pump and proportional valve, which are responsible for the operation of the jib.
As far as the electrical circuit diagram is concerned, everything is clear; power does not come from the driver to the coil, so the crane jib must stand still. This means that only the proportional valve and the hydraulic pump remain.
In the previous article we had to change the pump because replacing the valve didn't help. In this case, the problem turned out to be in the valve. The valve responsible for lowering the crane jib was replaced.
During the inspection of the proportional valve, small particles of dirt were found on the internal filter. Apparently, they disrupted the normal operation of the crane jib. How dirt (or small steel shavings) got there and why the main filters do not do their job remains to be seen.
While this article was being written, another cargo crane stopped working. The crane jib does not luffing up. The problem also turned out to be in the proportional valve.
With experience in operating cargo cranes of this model, it became clear that proportional valves in pump hydraulic systems are their weak point.
When a crane jib is luffing down under its own weight, it indicates a potential issue with the luffing mechanism or its components. Here are some steps to troubleshoot the problem:
1. Check the Hydraulic System
- Hydraulic Fluid Level: Ensure the hydraulic fluid is at the proper level. Low fluid can cause insufficient pressure to hold the jib in position.
- Hydraulic Pump: Verify that the hydraulic pump is functioning correctly. A malfunctioning pump can lead to inadequate pressure.
- Hydraulic Hoses and Connections: Inspect hoses and connections for leaks. A leak can cause a loss of hydraulic pressure.
- Hydraulic Cylinders: Check the cylinders for any signs of damage or wear. Leaking seals in the cylinders can result in pressure loss.
2. Inspect the Mechanical Components
- Luffing Winch: Ensure the winch is in good working condition. The winch drum and cables should be intact without excessive wear or damage.
- Brake System: Verify the brake system is operational. A faulty brake may not hold the jib in place.
- Luffing Gearbox: Check the gearbox for any signs of wear or damage that could affect its operation.
3. Examine the Control System
- Control Valves: Ensure that the control valves are functioning correctly. Faulty valves can lead to uncontrolled movements.
- Control Panel: Check the control panel and its components for any signs of malfunction. Ensure that all switches and indicators are working properly.
4. Structural Integrity
- Jib Structure: Inspect the jib structure for any signs of bending, cracking, or damage that could affect its balance and stability.
- Pins and Bushings: Check the pins and bushings for wear. Worn pins and bushings can cause excessive play and instability.
5. Load Test
- Perform a Load Test: Conduct a load test to verify the crane's performance under load. This can help identify issues that may not be evident when the jib is unloaded.
6. Consult the Manufacturer's Manual
- Manufacturer’s Troubleshooting Guide: Refer to the crane’s operation and maintenance manual for specific troubleshooting steps and recommendations from the manufacturer.
7. Professional Inspection
- Certified Technician: If the issue persists or if you are unable to identify the cause, consider having the crane inspected by a certified technician or service provider.
By following these steps, you can systematically identify and address the cause of the luffing down issue in your crane jib. Safety should always be a priority, so ensure all troubleshooting and repairs are conducted following appropriate safety protocols.
Crane model: DMC DDKC-3026-00 (Dongnam Marine Crane)
Also read other articles about DMC cargo cranes:
- Problems with cargo cranes. Some problems with cargo cranes that occur on the ship
- The cargo crane does not slew. Troubleshooting
- The crane hook goes up slowly. The cargo crane is not working. Troubleshooting
- PLC failure. The cargo crane does not start. Troubleshooting
- Motor Fault on the crane. Troubleshooting
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