Howo Mining Truck Hydraulic System Oil Leakage Troubleshooting
Howo mining trucks operate under heavy-load, high-dust and severe bumping conditions in mining areas. The hydraulic system is prone to oil leakage caused by aging seals, loose pipelines and worn components. Oil leakage falls into two categories: visible external leakage and hidden internal leakage. Below is a standardized troubleshooting procedure suitable for mining truck working scenarios, from safety preparation to pinpointing leak points and fault judgment, which is practical and operable to resolve faults of oil leakage in lifting, steering and brake hydraulic systems.
1. Safety Preparations Before Inspection (Mandatory)
The hydraulic system of mining trucks works at high pressure and heavy load. Safety measures must be implemented before inspection to avoid safety accidents and secondary faults:
Park the vehicle on firm and flat ground, shut down the engine and cut off power, pull the handbrake tight, install wheel chocks, fully release residual pressure of the hydraulic system, and wait for the system to cool down before inspection to prevent high-pressure oil jetting and high-temperature scalds.
Clean dust and oil contamination on the vehicle body and hydraulic components to avoid stains covering leak points and interfering with judgment. Prepare non-woven cloth, soapy water, pressure gauge, blanking plugs, wrenches and other inspection tools.
Record the oil level in the hydraulic oil tank. Compare the oil level drop after inspection to help judge the severity of oil leakage.
2. Full Inspection for External Oil Leakage (Dominant Fault, Priority Inspection)
External oil leakage can be directly located by visual check, touch and pressure test. It is the most common type of oil leakage on mining trucks. Focus on six key parts in the order from simple to complex:
2.1 Pipelines and Joints (Highest-Frequency Leak Points)
Vibration and bumping of mining trucks easily cause loose joints and fatigue cracking of pipelines, which are the primary inspection points for oil leakage. Check all threaded joints, flange joints and ferrule joints of high-pressure hoses, low-pressure return hoses and hydraulic hard pipes one by one:
Visually check for oil stains, soaked oil marks and oil sludge accumulation at joints. Slight seepage will form black oil sludge, while severe leakage leads to dripping oil.
Wipe joints and pipelines with clean non-woven cloth, start the hydraulic system at idle speed and low pressure (pressure ≤0.5MPa), and observe whether new oil seeps out. Pay key attention to pipeline bends, loose fixing clamps and pipelines worn by long-term friction.
Common faults: loose or stripped thread of joint, aging or damaged sealing ring, cracking of outer rubber layer of oil hose, bulging of inner steel wire and leakage at pipeline welding seams.
2.2 Hydraulic Cylinders
The lifting cylinders and steering cylinders of mining trucks bear stress during repeated stretching, so seals are prone to wear and oil leakage. Check two key positions:
Cylinder piston rod: Observe if there is oil film or oil beads on the piston rod surface, and whether oil stains remain after extension and retraction. If the piston rod has dull surface with oil traces, the rod wiper and oil seal are worn and leaking. Meanwhile, check scratches and rust on the piston rod; hard impurities scratching seals will cause continuous oil leakage.
Cylinder end cover and base mating surface: Check oil seepage at end cover bolts and cylinder body gaskets, which is usually caused by aging end cover gaskets or insufficient bolt tightening torque.
2.3 Hydraulic Pumps and Motors
The hydraulic pump is the core power component of the system. Shaft seals and housing seals are easy to fail: inspect the pump shaft extension, pump cover mating surface and inlet/outlet flange. If oil stains spread and oil sludge accumulates, it is mostly caused by worn pump shaft seal or damaged housing gasket. In severe cases, it is accompanied by overheating of the pump body and insufficient pressure.
2.4 Hydraulic Valve Bank
Directional valves, relief valves, pneumatic control valves and distribution valves are high-frequency fault points: check valve body mating surfaces, valve core end covers and pressure adjusting screws. Frequent operation of directional valves easily causes wear of internal sealing rings and dust-proof rings, resulting in seepage at gaps. Stuck valve spool or abnormal pressure regulation of relief valves may also cause external leakage of valves.
2.5 Hydraulic Oil Tank and Accessories
Check the tank cover gasket, oil drain screw, filter interface and oil level sensor mounting position for oil seepage. Focus on scratches and deformation on the tank sealing surface which leads to poor sealing and oil leakage. Also inspect the breather valve for blockage, to avoid pseudo oil seepage caused by negative pressure in the system.
2.6 Auxiliary Precision Leak Detection (For Micro Seepage)
For slight seepage invisible to naked eyes, adopt the soapy water leak detection method: evenly apply soapy water to all joints, sealing surfaces and valve gaps, start the hydraulic system and run at low pressure. The position with bubbles is the accurate leak point, suitable for hidden external micro-seepage faults of mining trucks.
3. Inspection for Internal Oil Leakage (Hidden Fault, Easy to Neglect)
Internal leakage leaves no external oil stains. It will cause symptoms such as weak lifting, slow steering, system pressure drop and abnormal temperature rise. It needs to be inspected through pressure holding test, sectional isolation and pressure measurement, mainly checking internal leakage of cylinders, valve bank and pump.
3.1 Overall System Pressure Holding Test
Start the hydraulic system, raise the system to rated working pressure, cut off oil passages of all actuators, hold pressure statically for 10 minutes and observe the pressure gauge reading. For a normal system, pressure drop ≤5%. Rapid pressure drop indicates internal leakage in the system.
3.2 Sectional Isolation to Locate Internal Leakage Area
Adopt sectional blocking method to narrow the fault range, isolate the lifting circuit, steering circuit and auxiliary oil circuit one by one. If the pressure holding performance of the system is obviously restored and pressure no longer drops rapidly after blocking a certain circuit, internal leakage exists in this circuit.
3.3 Special Inspection for Internal Leakage of Core Components
Cylinder internal leakage: Raise the cylinder to the middle position and fix it, block the upper and lower chamber oil passages of the cylinder and hold pressure to observe pressure change. Rapid pressure drop means worn piston sealing rings and cross-flow between high-pressure and low-pressure chambers, manifested as automatic sinking and pressure relief of the cargo box after lifting.
Valve bank internal leakage: Disassemble and check the fit clearance between valve spool and valve bore. Worn valve spool, damaged seal grooves and stuck impurities will cause internal leakage inside the valve, leading to insufficient system pressure and slow action.
Hydraulic pump internal leakage: Detect pressure difference between pump inlet and outlet. If no-load pressure is normal but pressure drops greatly under heavy load together with severe pump overheating, the internal valve plate and plunger are worn with serious internal leakage.
4. Oil Leakage Fault Classification and Inspection Completion
4.1 Fault Classification
Slight seepage: Only surface oil stains, no dripping oil, no obvious oil level drop, no impact on equipment operation; seals can be replaced at proper time.
Moderate oil leakage: Dripping oil, slow oil level drop, slight slowdown of equipment action; stop the machine immediately for maintenance.
Severe oil leakage: Heavy dripping, rapid pressure drop, sharp temperature rise and action failure; shut down the machine immediately, forbid operation and carry out emergency maintenance.
4.2 Inspection Completion Specifications
After inspection, clean oil contamination on equipment, replenish hydraulic oil of the same model, start the equipment for no-load and load trial run, and check system pressure and operating status. Resume normal operation only after confirming no internal or external oil leakage, no abnormal overheating and stable pressure. Record leak positions and fault causes for subsequent preventive maintenance.
5. Summary of Common Causes of Oil Leakage for Howo Mining Trucks
Combined with working conditions of Howo mining trucks, oil leakage is mainly caused by three factors: first, dust and impurities entering the system, wearing seals and jamming valve spools; second, long-term heavy-load bumping resulting in loose pipelines and fatigue aging of seals; third, improper selection or deterioration of hydraulic oil accelerating corrosion and failure of seals. After troubleshooting and maintenance, filter oil, fasten pipelines and perform regular oil change to reduce recurrence.