The truck mounted cranes frequently encounter problems during construction site operations, such as insufficient lifting capacity, failure to reach rated lifting capacity, and slow lifting movements. While these issues don't directly cause equipment downtime, they can severely slow down construction progress. Incorrectly diagnosing the problem can also lead to unnecessary replacement of parts and increased maintenance costs.
This article, aimed at equipment maintenance engineers, purchasers, and fleet managers, outlines the causes of failures, standardized troubleshooting procedures, common misconceptions, and preventative maintenance solutions to help quickly locate problems and reduce equipment downtime losses.
Fault Attribution: Operation or Equipment?
Before disassembling hydraulic components, prioritize ruling out external factors that are not related to equipment damage, as many powerlessness issues stem from improper use.
- Overload Working Conditions: Excessive boom extension or working radius significantly reduces actual lifting capacity, making the crane feel underpowered.
- Unstable Outrigger Support: Fully extended outriggers or soft ground trigger the torque limiter protection system, automatically limiting hydraulic output.
- Abnormal Power Take-Off Shaft (PTO) Input: Incomplete PTO engagement or insufficient air pressure can prevent the hydraulic pump from achieving full power output, leading to a decline in overall crane performance.
⚠️Note: If the no load operation is smooth, but the system immediately becomes weak when loaded, it is most likely due to an abnormality in the pressure build up of the hydraulic system; if the no load operation is also slow and weak, the oil supply and power input links should be checked first.
Main Hydraulic Causes of Insufficient Lifting Force
1. Fuel Supply Circuit Malfunction
- Insufficient hydraulic oil level or clogged suction filter: This obstructs oil pump suction, resulting in insufficient flow and sluggish machine operation.
- Contaminated hydraulic oil: Impurities in the oil cause valve core sticking, accelerating internal wear of the pump and valves, and leading to internal leakage.
- Air in the oil circuit: Air entering the system causes vibration and unstable lifting force.
2. Pressure Control Component Failure
- If the relief valve's pressure setting is too low, the valve core is stuck, or the spring fails, the system cannot build up the rated working pressure, and high pressure oil flows directly back to the oil tank.
- Internal wear and seal failure in the multiway directional valve causes internal leakage, resulting in rapid pressure drop under load, a fault easily overlooked.
- A stuck balance valve or a blocked damping orifice can cause the hoist and luffing mechanism to become powerless independently.
3. Wear And Internal Leakage Of Actuators
- Hydraulic pump wear: Reduced volumetric efficiency and decreased load pressure are common failure points.
- Aging and damage to the seals of the luffing and telescopic cylinders cause internal pressure leakage; under load, the boom slowly sinks accompanied by weak lifting.
- Internal wear of the winch motor results in weak winch lifting, while other crane functions normally.
How To Troubleshoot And Resolve Faults
| Step | Testing Items | Judgment Criteria | How to Solve |
| 1 | Operating conditions and power checks | Check the load chart and inspect the air pressure and engagement status of the outriggers and power take off unit. | Correct operating conditions and repair power take off air circuit malfunctions. |
| 2 | Hydraulic oil and filter element | The oil level is within the acceptable range, the oil is free of black impurities, and the filter element is not clogged. | Add oil, replace hydraulic oil and filter element, and bleed the system. |
| 3 | System pressure testing | Connect an external pressure gauge to read whether the working pressure under load has reached the equipment's rated value. | If the pressure is insufficient, continue to position the valve and pump body downwards. |
| 4 | Valve assembly testing | Check for abnormal overheating in the relief valve and multiway valve, and whether there is any internal leakage. | Clean the valve core, replace the seals, and replace the entire valve assembly if necessary. |
| 5 | Actuator component testing | Test the luffing, telescopic, and hoisting mechanisms separately to determine whether the problem is with the entire machine or a single mechanism. | Inspect the cylinder seals and winch motor; if severe wear occurs, replace the entire assembly. |
Common Maintenance Mistakes to Avoid
1. Replacing the hydraulic pump immediately upon encountering insufficient lifting capacity
Many real faults stem from internal leakage in the relief valve or multi-way valve. Blindly replacing the pump will not solve the problem and will only increase the cost of spare parts.
2. Unauthorized increase of the relief valve pressure to forcibly increase lifting capacity
Exceeding the factory set pressure can cause cylinder and oil pipe bursts, posing a significant safety hazard. Unauthorized pressure increases are strictly prohibited.
3. Ignoring hydraulic oil quality
Oil contamination is the source of wear and tear on valves and pumps. Repairing only the fault without changing the oil will lead to a recurrence of the problem in a short period.
Preventive Maintenance Tips
- Replace hydraulic oil, return oil filter, and suction oil filter according to the equipment manual's recommended schedule, and periodically check oil cleanliness.
- Before daily operation, check hydraulic line joints for leaks, and observe outriggers and boom for signs of slippage or sinking; identify seal aging early.
- Regularly calibrate the system working pressure, ensuring the relief valve pressure maintains the original factory calibration value.
- Strictly adhere to the load curve during operation, avoid prolonged overloading, and slow down the wear rate of hydraulic components.
Conclusion
A truck mounted crane's inability to lift is not usually due to a single component failure. First, external factors such as operating conditions, outriggers, and power take off (PTO) should be ruled out. Then, a thorough inspection should be conducted, starting with the hydraulic supply circuit and pressure control valves, and progressing to the actuators. Using a pressure gauge to measure the system pressure can quickly pinpoint the fault location, avoiding unnecessary replacement of parts.
During maintenance, it is strictly forbidden to modify the system pressure without authorization. Regular replacement and filtration of the hydraulic oil are also crucial to reduce wear on hydraulic components, lower the probability of equipment downtime, and ensure the long term stable operation of the truck mounted crane.
