Troubleshooting of two faults of the WL60 excavator

Fault I: At the beginning of operation, both driving and steering were normal. However, after working for a long time, the steering became heavy

In August 1998, a certain excavator of a certain unit was shuttling back and forth at the construction site for construction work every day. During this period, excavators have continuously encountered the problem that their driving and steering functions are normal at the beginning of the day, but after working for a long time, they experience heavy steering. According to the driver's report, at that time, it was suspected that the volumetric efficiency of the steering system had decreased. So, the pressure of the relief valve was adjusted successively, and the piston oil seals of the steering pump and steering cylinder were replaced, but the problem still remained unsolved. Based on the situation introduction, it is initially believed that this is a frequent and progressive fault. When the malfunction occurred, an inspection was carried out and no serious problems were found. Only the oil inlet pipe of the steering pump had aged. When the temperature of the hydraulic oil was high, the pipe became soft, bent and sucked in, causing poor oil flow and resulting in a lack of oil in the steering system, leading to heavy steering. After replacing the oil pipe, the mechanical steering performance immediately returned to normal.

So, why can the excavator move and turn normally when it first starts working before pipe replacement? This is because the hydraulic oil for the machine's steering and the hydraulic oil for the working device's control system share one oil tank. During the day, the temperature is high, and the hydraulic oil works frequently, causing the oil temperature to rise and making the oil pipes "soft". At night, the hydraulic oil and hydraulic components cool down through heat dissipation, causing their temperature to drop. The oil pipes naturally "harden", and at this point, the oil intake of the steering pump becomes smooth. Therefore, the excavator's operation and steering return to normal the next day.

Fault II: The engine stops every 4 to 5 buckets during the excavation operation

A strange phenomenon occurred during the operation of an excavator: when it was digging, the engine would shut down every 4 to 5 buckets. When the engine is restarted and the operation is resumed, the above phenomenon is still repeated. The driver inspected the fuel line as usual but failed to find the cause of the fault. During the maintenance, we first conducted a test with a pressure gauge to rule out the possibility of pressure overload in the operating system of the working device. Then check if the fuel line of the engine is unobstructed. That is, after the engine is turned off, disassemble and inspect the diesel filter. If no fuel is found, it is obvious that the problem lies between the filter and the diesel tank. So the oil pipe was removed from the diesel tank and placed in another oil bucket. When the test was conducted again, the fault phenomenon disappeared.

I opened the diesel tank and took out a plastic cigarette wrapper from inside. At this point, the cause of the malfunction has become clear: it is due to the plastic paper being free or suspended in the oil during normal times. When the engine starts, the rotational speed is relatively low, and the suction force at the oil suction port in the diesel tank is weak. The plastic paper is sucked near the oil suction port and has not (or has not completely) blocked the oil port. As the oil transfer pump has a strong pumping capacity, it can quickly fill the filter with oil, and the engine can start smoothly. When the engine is operating at full load, the fuel consumption is high. The suction force at the oil suction port in the diesel tank increases, and the plastic paper is sucked to the oil suction port and completely seals it. The fuel transfer pump can no longer pump oil. Therefore, most of the fuel used in the first few buckets of digging operations is in the filter. When 4-5 buckets are dug, the fuel in the filter is exhausted, and the engine naturally shuts down. After the engine was turned off, the plastic paper left the oil suction port again. This cycle continued, causing the above-mentioned malfunction phenomenon.