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16/05/2024

The crane jib is luffing down under its own weight. Troubleshooting

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.

The crane jib is luffing down under its own weight. Troubleshooting

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.

Crane joystick
Crane joystick

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.

Crane hydraulic brake solenoids
Crane hydraulic brake solenoids

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.

Crane hydraulic brake solenoids (diagram)
Crane hydraulic brake solenoids (diagram)
Solenoid operation diagram
Solenoid operation diagram

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.

Driver operation diagram
Driver operation diagram
Checking the solenoid coils
Checking the solenoid coils

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.

Luffing hydraulic pump
Luffing hydraulic pump
Proportional valve
Proportional valve

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.

Disassembling the proportional valve
Disassembling the proportional valve
Valve and filter
Valve and filter
Valve disassembly
Valve disassembly

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.

Crane model: DMC DDKC-3026-00 (Dongnam Marine Crane)

Also read other articles about DMC cargo cranes:

  1. Problems with cargo cranes. Some problems with cargo cranes that occur on the ship
  2. The cargo crane does not slew. Troubleshooting
  3. The crane hook goes up slowly. The cargo crane is not working. Troubleshooting
  4. PLC failure. The cargo crane does not start. Troubleshooting
  5. Motor Fault on the crane. Troubleshooting

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