Evening people I’ve a kobelco sk85 that will bog down on all Hyd circuits no noisy pumps , but when you lift the boom up the dipper will slowly move out too , but machine is fitted with check valves all over . If you were to lay the arm completely out it will stall the machine , filters changed , nothing untoward on first sight has anyone any suggestions ?? Cheers
When you lift boom, pressure bypasses internally to dipper circuit due to worn valve spools or seals making dipper extends unintentionally. Internal leakage so severe that pump can't keep up and bogs engine trying to generate pressure that's immediately dumping internally. Your problem is upstream in the main valve body where circuits are cross-connecting. Pressure test each circuit individually: Boom circuit should hold ~3500 psi under load. If boom pressure is low AND dipper pressure shows unexpected reading = cross-contamination confirmed Isolate functions: Disconnect dipper lines at valve see if boom still causes movement elsewhere, valve body leaking internally Fix: Main control valve rebuild or replacement-seals, spools, possibly valve body itself. SK85 valve work is major repair: 8-16 hours labor + parts ($1500-4000 depending on damage extent)
When you say it stalls the machine, that makes me think it's a pressure problem. I'd probably look at the main relief valve first. It might be stuck closed. The dipper moving on its own is a classic sign of an internal leak, maybe in your main valve block.