How to troubleshoot and repair slow operation issues in Liebherr excavators

Case 1: Slow operation of the entire excavator Causes of failure: 1 Main relief valve spring broken or plunger stuck in the open (relief) position 2 Air trapped in the pump (cavitation/suction of air) 3 Main pressure valve severely worn or clearance too large 4 Malfunction of the main relief valve on the valve block 5 Damaged O-ring Repair methods: 1 Replace the main relief valve 2 Bleed air from the pump 3 Replace or repair the main pressure valve 4 Replace or repair the main relief valve Slow operation of the entire excavator Case 2: Causes of failure: 1 Pilot control oil circuit pressure too low 2 Main pump pressure too low, causing slow operation of the entire machine 3 Hydraulic circuit obstruction; hydraulic oil filter element clogged, causing slow operation of the entire machine Repair methods: 1 Measured self-reducing valve pressure; disassembly revealed the internal copper mesh screen was clogged 2 Hydraulic oil emulsified and degraded; contained water and impurities 3 Hydraulic oil filter element clogged; copper mesh detached; significant impurities in the hydraulic oil tank 4 Root cause: “Hydraulic oil filter element clogged” 5 Solution: “Flush the hydraulic system 2–3 times; replace hydraulic oil and filter element” Liebherr Excavator Repair Company (Guiyang, Guizhou) Case 3: Slow excavator bucket operation Analysis of failure causes: 1 If the excavator bucket operates slowly or lacks power, first check if the output pressure of the PPC valve is normal (normal value: 2.7 MPa) 2 If normal, further check if the movement of the bucket spool in the control valve is smooth 3 If smooth, continue to check if the pressure compensation valve is functioning correctly or if the pressure compensation plunger moves smoothly 4 If functioning correctly, check if the leakage rate of the bucket cylinder is within normal limits 5 If the answer is “Yes,” the cause of the slow bucket movement is a malfunction of the safety and inlet valve; it requires repair or replacement. Further reading: 1 If the answer to step 1 is “No,” the PPC valve is faulty and requires replacement. 2 If the answer to step 2 is “No,” the control valve spool is malfunctioning and requires repair or replacement. 3 If the answer to step 3 is “No,” the pressure compensation valve or plunger is malfunctioning and requires repair or replacement. 4 If the answer to step 4 is “No,” the bucket cylinder piston seal is defective and requires repair or replacement. [Case 4] Excavator movements are slow and lack power Analysis of fault causes 1 Slow and weak excavator movement in Hyundai excavators is generally caused by a malfunction of the main relief valve. 2 The main relief valves on these excavators are pilot-operated; common reasons for malfunction include: ① Abnormal pressure setting ② Wear on the poppet valve’s conical surface ③ Clogged damping orifice in the pilot spool ④ Broken springs, etc. 3 These are the common causes of slow and weak movement in Hyundai excavators. So, what should a technician do when this fault occurs during operation? How can the cause be identified and the problem resolved? Our factory’s Hyundai excavator repair experts offer the following advice. 4 When this fault occurs, first swap the suspected faulty main relief valve with a known good one and test the machine; if the fault moves to the other circuit, the main relief valve is confirmed as the cause. 5 If the fault does not move after swapping, further troubleshooting is required. Further reading: Slow and weak boom movement Common causes: 1 Blockage in the hydraulic circuit. 2 Leakage in the hydraulic circuit (caused by seal failure, improper assembly, loose fittings, deteriorated O-rings, etc.). 3 Internal leakage in the boom control spool or cylinder causing slow and weak boom movement. 4 Internal leakage in the boom cylinder. 5 Problem with the boom control spool.