Fault Phenomenon: Komatsu PC300 excavator boom speed is normal when operated alone, but weak under combined operation or heavy load.

Troubleshooting Process:
– Checked main pump: dual pump merging logic error.
– Checked LS valve: LS selector valve stuck.
– Checked relief valve: main relief pressure set too low.
– Checked cylinder: boom cylinder internal leakage.

Root Cause: The LS selector valve is stuck, preventing the two pumps from correctly merging flow to supply the boom cylinder, halving the flow.

Required Parts: Clean or replace LS selector valve.