The primary control valve was removed and subsequently repaired externally. Following its repair, the control valve was reinstalled on the machinery, but upon attempting to slowly raise the machine's boom, we encountered issues with alignment and leveling. Despite attempts to rectify the problem by replacing the hydraulic pump, handle assembly, and main arm cylinder seal, the issue persisted. Hydraulic maintenance personnel were brought in, yet their efforts also failed to resolve the malfunction, which had persisted for over three months, leaving the equipment inoperable.
In search of an effective solution, we reached out to specialized distributors who could provide expert assistance. During on-site testing, I observed that the large arm moved sluggishly when operated independently, with a lifting time of 48.5 seconds in performance tests. However, the forearm and bucket performed adequately under similar conditions. When both arms were used together, the forearm seemed faster than expected, while the large arm barely moved. Only once the forearm initiated movement would the large arm begin to lift.
Based on these observations, it appeared that the issue arose when combining the actions of both arms rather than in operating each arm individually. Further investigation revealed that during the boom lift, Pump 2 registered a pressure of 30MPa, whereas Pump 1 showed only 4MPa. This indicated no convergence between the two pumps during the lifting action.
Upon inspecting the logic valves responsible for coordinating the main arm movements, it became evident that the oil line PB was incorrectly connected to the adjacent DR5 line. Even after correcting this error, there was still no convergence between the pumps during the lift (Pump 1 pressure remained at 4MPa). Using a hydraulic gauge, we measured the pressure at the logic valve’s PB port and found it to be zero during the lift.
Further analysis suggested that the lack of pressure at the PB port during the lift might stem from either the pilot selector valve or the solenoid valve controlling the merging and cutting of the upper arm. Upon examining the pilot selector valve, we discovered that the solenoid valve responsible for merging and cutting the upper arm was stuck in the closed position (normally open).
After cleaning and resetting the solenoid valve, it returned to normal operation. However, subsequent measurements showed that the pressure at the logic valve’s PB port was still zero during the lift. Observing this, we noted that during the lowering of the arm, the pressure at the PB port was 4MPa, suggesting a possible misconnection in the upper arm’s oil lines.
A thorough review of the oil lines uncovered an incorrectly installed high-arm oil line at the shuttle valve block. Correcting this installation restored normal pressure at the logic valve’s PB port. Further testing showed that the lifting speed of the upper arm was now normal, but the combined action remained sluggish. This led us to suspect that the forearm merging valve was not properly disengaged during the lift. Measuring the pressure at the forearm’s 2PX port from the forearm merging valve yielded 0MPa. Upon inspecting the pipeline, we found that the 2PX hose of the forearm merging valve was incorrectly connected to the DR1 oil port of the main control valve.
After a series of meticulous checks, it became clear that the failure stemmed from a misconnection of multiple hydraulic lines during the reassembly of the main arm merging solenoid valve after its disassembly and cleaning. Engaging professional distributor outsourcing engineers proved invaluable. With their expertise, the incorrectly installed hydraulic oil line was corrected, and during a follow-up performance test, the lifting time of the upper arm dropped to 2.8 seconds. The arm’s performance was fully restored, and the fault was finally resolved.
To summarize, contacting experienced distributor engineers is crucial for resolving such intricate issues. It is also important to remember that when replacing, disassembling, or repairing the main control valve’s oil lines, one must exercise caution and avoid overconfidence without proper markings. Incorrect installations can lead to complex failures and unnecessary economic loss. These mistakes can easily be avoided with diligence and attention to detail!
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