A mining site reported a critical safety issue on a Shantui SL50W wheel loader. When driving straight, the machine would slowly drift to the right, requiring the operator to hold the steering wheel off-center to drive straight. Additionally, the hydraulic oil temperature was exceeding 90°C, causing the hoses to weep.
The technician began by testing the steering cylinder. He disconnected the lines and capped the ports. The drift stopped, proving the cylinders were sound. He then focused on the "Priority Valve." In the SL50W, the steering pump sends oil to a priority valve, which ensures the steering gets oil before the implement (bucket) system. If this valve fails, the steering circuit loses priority.
He removed the priority valve cartridge. The spool was found to be stuck in the "Implement Priority" position by a burr of metal. This meant the steering circuit was being starved of oil, receiving only residual leakage flow. The "drift" was actually the machine tracking due to the differential in the axle, as there was insufficient oil pressure to center the steering valve.
Furthermore, the starvation caused the pump to cavitate. The technician checked the suction hose from the tank to the pump. The hose felt soft. Upon cutting it open, he found the inner liner had delaminated and collapsed. This restricted the intake flow, causing the cavitation noise and heat.
The repair involved honing the priority valve bore to remove the burr, installing a new priority spool, and replacing the suction hose with a high-pressure reinforced hose. The hydraulic tank was flushed, and the system was refilled with clean oil. After starting, the steering became firm and responsive, and the temperature stabilized at a normal 65°C.
