A limestone quarry reported that a Liugong CLG862H wheel loader's steering wheel would not return to center after a turn (steering drift). Additionally, the lift cylinder was slow to raise the boom, especially when the engine was idling.
The technician diagnosed the "Steering Priority System." In this loader, the steering pump supplies oil to a "Priority Flow Control Valve." This valve ensures the steering gets oil first, and any excess goes to the implement (lift) circuit. He removed the priority valve. He found the "Positioning Pin" inside the valve housing was sheared. This pin holds the valve spool in the neutral position. Without it, the spool was floating, constantly bypassing oil to the tank instead of steering the machine. This caused the steering cylinder to "float" or drift, and the steering wheel to lose center.
The "Slow Lift" issue was traced to the "Hydraulic Suction Strainer." The suction strainer is located inside the hydraulic tank. The quarry air is dusty, and the hydraulic tank breather was missing. Dust entered the tank and clogged the strainer. The clogged strainer restricted the flow to the pump, causing the pump to "starve" (cavitate). This resulted in low system pressure and slow lift speed.
The repair involved replacing the priority valve spool and positioning pin. He also removed the hydraulic tank, cleaned the suction strainer with solvent, and installed a new tank breather cap. The hydraulic oil was replaced. After reassembly, the steering returned to center instantly, and the lift speed matched the specification.
