The rove RT600E crane has a hook automatic descending fault in operation.
Inspection revealed that as soon as the engine was started, the hook began to descend and the "searing" oil flow could be heard at the reversing valve and in the cab.
The phenomenon disappeared after the engine went out.
The analysis shows that the hook no longer drops after the engine flameout, indicating that the hoist brake has no problem.
According to the hydraulic system diagram of the machine, only when the control handle moves the pilot oil into the control valve can the hoist brake be opened.
Since the lowering of the hook does not require electrical control, it can also eliminate the possibility of electrical fault, the problem should be in the hydraulic system.
By analyzing the hydraulic system diagram, the fault point should be judged between the control handle of the cab and the winch reversing valve.
First, the pilot control of the bridge control handle control road, to observe the oil flow.
When the handle is in the middle position, there is no oil flow in the tubing to control the drop of the hook, which means there is no problem with the handle control.
It is found that a self-locking spring breaks in the main valve core, causing the hook to fall automatically due to self-locking failure.
The machine has three sets of control valves, one of which is the backup valve.
The backup valve has the same components as the winch control valve, and no tubing is installed.
Since no accessories were available at that time, one spring of the backup valve was removed and installed in the winch reversing valve.
After the crane was repaired, although the test machine was normal, the engine would stop automatically. At the same time, when the hook was lowered, it would tremble, and the engine could not start after the engine stopped automatically.
After the force extractor is cut off, the startup is normal. After the force extractor is switched on, it cannot be started.
The analysis of the hydraulic chart shows that the spare valve is not connected with any tubing, but the oil output from the hydraulic pump will flow through the spare valve.
If the backup spool action, the oil flow will impact the winch reversing valve, causing the hook to shake.
At the same time, the spool does not have a spring to automatically return to the position, leading to increased load, insufficient power of the engine, or even start.
When the spring in the backup valve is installed, the fault disappears.
This discharge process shows that the spring in the backup valve is also useful, not easy to remove.