Slow Main Luffing Lowering of SCS1000A – Unit CC0100CF0070

Item	Details
Fault Type	Hydraulic Fault
Equipment Code	CC0100CF0070
Model	SCS1000A
Business Unit	Hoisting Machinery Business Unit
Product Group	40/Crawler Crane/Crawler Crane
Operating Hours	236 H
Shutdown Fault	No
Location	Singapore
Public Status	Display
Service Order	2506021124

Fault Description

Main boom lifting functions normally, but lowering operation is extremely slow.

Fault Phenomenon

On June 26, 2025, one SCS1000A crawler crane (unit CC0100CF0070) with 236 operating hours in Singapore showed normal main boom lifting speed, but extremely slow boom lowering speed.

Troubleshooting Logic

Possible causes for slow main luffing lowering include electrical and hydraulic factors:

1. Low pressure at the lowering side of the main luffing joystick.
2. Abnormal pressure sensor or wiring at the lowering side of the main luffing joystick.
3. Malfunction of the main luffing lowering proportional solenoid valve.
4. Low relief pressure of the main luffing lowering circuit.

Basic Principle of Main Luffing Lowering

1. Electronic positive flow control: main pump displacement is proportional to control current.
2. Main luffing winch speed relates to joystick opening, which affects joystick pressure sampling.
3. Joystick pressure further influences control current to the main pump and main valve.

In the diagram:

• No.8: Main luffing lowering relief valve
• No.16: Main luffing lowering proportional solenoid valve

Troubleshooting Process

1. Based on site feedback, boom lifting was normal, boom lowering had movement without pressure build‑up but only slow speed, indicating the brake was fully released.
2. On‑site service checked the IO interface; pressure values for raising and lowering of the luffing joystick were both around 30 Bar, confirming no abnormality in the lowering pressure sensor and wiring.
3. During lifting and lowering operation, main pump feedback AD value reached approximately 480, verifying main pump displacement met lowering demand.
4. IO interface inspection showed main luffing lowering proportional solenoid valve AD feedback reached around 400, confirming normal solenoid valve wiring.
5. Removed the main luffing lowering proportional solenoid valve from the main valve, cleaned it with spray cleaner, and reinstalled. Main luffing lowering speed returned to normal.

Troubleshooting Summary

For both SCS and SCA series crawler cranes, electrical control is highly integrated. Before troubleshooting, always verify whether electrical conditions for each function are satisfied. Only after confirming no electrical faults should hydraulic troubleshooting proceed, to ensure efficient fault resolution and avoid unnecessary fluid contamination.