For small excavators, flexibility and maneuverability are their advantages, but “inability to walk” is the most troublesome problem for machine owners. Obviously the engine roars normally, but once it climbs a slope or encounters an obstacle, the track becomes “soft”, which not only delays the construction period, but may also indicate a potential serious failure. The root causes of the inability of small excavators to move are usually concentrated in the hydraulic system, transmission mechanism and operating habits. The following six reasons are the most common.
1. “Internal damage” to the hydraulic system: loss of pressure and flow, and inability to walk. 80% of the faults are caused by the hydraulic system.
Main pump wear or variable mechanism failure: the walking speed of the small excavator depends on the flow and pressure output by the hydraulic pump. After the plunger and valve plate in the pump are worn for a long time, the internal leakage intensifies, and the high-temperature hydraulic oil directly flows from the high-pressure area back to the low-pressure area, resulting in insufficient flow of the traveling motor and slowing down the speed. If the servo piston of the variable pump is stuck, it will not be able to automatically adjust the displacement according to the load, which will also cause it to be powerless at full load.
Safety valve (relief valve) leakage: If the set pressure of the safety valve on the walking motor integrated block drops, or the valve core is worn and does not close tightly, once it encounters resistance, the system pressure will overflow before it reaches the rated value, and the driving force will be greatly reduced instantly.
Internal leakage of the central rotary joint: This is a unique failure point of small excavators. The rotary joint is responsible for transmitting hydraulic oil from the upper vehicle to the lower vehicle travel motor. After the internal sealing ring is worn, the oil circuits between the upper and lower vehicles will be colluded, causing the oil pressure flowing to the lower vehicle to be shunted, manifesting as walking deviation or unilateral weakness.
2. Traveling motor and final drive: loss of mechanical efficiency
If the hydraulic system pressure is normal, the problem lies at the end of the power transmission.
Motor plunger or bearing wear: After the plunger and cylinder inside the traveling motor are worn, the volumetric efficiency decreases. Even if the pressure is sufficient, the output torque cannot be effectively converted into driving force.
Final drive gear oil emulsification or gear wear: If water enters the final drive reduction box, the gear oil will emulsify and lubrication will fail. The gears and bearings will wear abnormally and produce excessive metal shavings, resulting in a sharp reduction in transmission efficiency and heavy and weak walking. This is the result of long-term wading operations or neglect of maintenance.
3. The neglected “track tension force”
This is often overlooked. If the track tensioning cylinder leaks oil and causes the track to be too loose, when the drive wheel rotates, the track shoe cannot engage with the drive teeth tightly, and “slip” or “tooth skipping” will occur. At this time, the engine speed is normal, but the driving force is wasted in the “empty position” between the crawler track and the drive wheel, which is manifested as slow walking and severe crawler shaking when climbing.
4. Operating habits and fuel system
Insufficient engine power: Don’t ignore “heart” problems. A clogged diesel filter, a failed turbocharger, or the throttle cable is not in place, which will cause the engine to seriously decelerate when loaded and unable to provide sufficient input power to the hydraulic pump.
Improper operation: When the car is cold, the viscosity of the hydraulic oil is high. If the engine is not fully warmed up and the machine is driven with heavy load, it will become weak due to excessive internal resistance.
Suggestions for troubleshooting (from simple to complex): first check the tightness of the track and engine deceleration; then measure the travel motor safety valve pressure; if one side is weak, focus on checking the sealing of the central rotary joint; if both sides are weak, test the output flow and pressure of the main pump.
In short, the inability to walk on a small excavator is a comprehensive disease. Only by peeling off the cocoon layer by layer according to the logic of “oil circuit-pressure-mechanical wear” can we avoid wasting money on replacing the assembly and accurately repair the chronic “weak legs” disease.
