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The Grove RT600E crane experienced a hook automatic lowering failure during operation. The inspection found that as soon as the engine was started, the hook began to drop, and the sound of "squeaking, squeaking" oil flow could be heard at the reversing valve and in the cab. This phenomenon disappears after the engine is turned off.

Analysis believes that the hook no longer drops after the engine is turned off, indicating that there is no problem with the winch brake. After analyzing the hydraulic system diagram of the machine, it can be concluded that the hoist brake can be opened only when the control handle moves and the pilot oil enters the control valve. Since the hook lowering does not require electrical control, the possibility of electrical failure can also be ruled out. The problem should be in the hydraulic system.

By analyzing the hydraulic system diagram, it is determined that the fault point should be between the cab control handle and the winch reversing valve. First, disassemble and inspect the pilot control oil circuit of the cab control handle and observe the oil flow. When the handle is in the neutral position, there is no oil flowing from the oil pipe that controls the hook's descent, which means there is no problem with the handle control. Then the winch reversing valve was dismantled and inspected, and it was found that a self-locking spring in the main valve core was broken, causing the hook to automatically drop due to self-locking failure.

This machine has 3 sets of control valves with the same structure as the winch control valve, one of which is a backup valve. The backup valve contains the same parts as the hoist control valve and does not have any oil pipes installed. Since there were no accessories at the time, a spring in the spare valve was removed and installed into the hoist reversing valve. The machine was tested again and the hook automatically dropped and the fault disappeared.

Although the crane tested normal after repair, the engine automatically stalled, the hook trembled when lowered, and the engine failed to start after automatically stalling. After cutting off the power take-off, it starts normally. After turning on the power take-off, it fails to start.

Analysis of the hydraulic diagram revealed that although the backup valve is not connected to any oil pipe, the oil output by the hydraulic pump will flow through the backup valve. If the backup valve spool moves, the oil flow will impact the hoist reversing valve, causing the hook to tremble. At the same time, because the valve core has no spring and cannot automatically return, the load increases, the engine lacks power, and even cannot start.

After installing the spare valve inner spring, the fault disappeared. This troubleshooting process shows that the spring in the spare valve is also useful and cannot be easily removed.

The Grove RT600E crane experienced a hook automatic lowering failure during operation. The inspection found that as soon as the engine was started, the hook began to drop, and the sound of "squeaking, squeaking" oil flow could be heard at the reversing valve and in the cab. This phenomenon disappears after the engine is turned off.

Analysis believes that the hook no longer drops after the engine is turned off, indicating that there is no problem with the winch brake. After analyzing the hydraulic system diagram of the machine, it can be concluded that the hoist brake can be opened only when the control handle moves and the pilot oil enters the control valve. Since the hook lowering does not require electrical control, the possibility of electrical failure can also be ruled out. The problem should be in the hydraulic system.

By analyzing the hydraulic system diagram, it is determined that the fault point should be between the cab control handle and the winch reversing valve. First, disassemble and inspect the pilot control oil circuit of the cab control handle and observe the oil flow. When the handle is in the neutral position, there is no oil flowing from the oil pipe that controls the hook's descent, which means there is no problem with the handle control. Then the winch reversing valve was dismantled and inspected, and it was found that a self-locking spring in the main valve core was broken, causing the hook to automatically drop due to self-locking failure.

This machine has 3 sets of control valves with the same structure as the winch control valve, one of which is a backup valve. The backup valve contains the same parts as the hoist control valve and does not have any oil pipes installed. Since there were no accessories at the time, a spring in the spare valve was removed and installed into the hoist reversing valve. The machine was tested again and the hook automatically dropped and the fault disappeared.

Although the crane tested normal after repair, the engine automatically stalled, the hook trembled when lowered, and the engine failed to start after automatically stalling. After cutting off the power take-off, it starts normally. After turning on the power take-off, it fails to start.

Analysis of the hydraulic diagram revealed that although the backup valve is not connected to any oil pipe, the oil output by the hydraulic pump will flow through the backup valve. If the backup valve spool moves, the oil flow will impact the hoist reversing valve, causing the hook to tremble. At the same time, because the valve core has no spring and cannot automatically return, the load increases, the engine lacks power, and even cannot start.

After installing the spare valve inner spring, the fault disappeared. This troubleshooting process shows that the spring in the spare valve is also useful and cannot be easily removed.