Komatsu PC3000-6 PC4000-6 Main Control Valve Control valves for large excavators. Compatible with Komatsu PC3000 and PC4000 models. Part Numbers: 65516840, 65516740, 90774240 Common Failures & Diagnostics Single function weak or slow movement: Caused by worn spool, overload relief valve, or pressure compensator. Boom/arm drift: Test cylinder seals first, then inspect anti-drift valves. All functions slow & low pressure: Check main relief valve, LS bypass valve, and unloading