In the maintenance and inspection of cranes, the use of compressed air is a practical and effective method to detect faults in various components. This method can help quickly identify problems, improve maintenance efficiency, and ensure the safe and reliable operation of cranes. The following is a detailed introduction to how to use compressed air to check the faults of crane-related components.
1. Determining the Faulty Part Causing Insufficient Cylinder Pressure in an Internal Combustion Engine
Insufficient cylinder pressure in an internal combustion engine is usually manifested as difficulty in starting the engine, weak operation, decreased power, increased fuel consumption, and the emission of black or white smoke. The parts that can cause insufficient cylinder pressure in an internal combustion engine include: a burnt cylinder head gasket, improper valve closure, piston ring blow-by, excessive wear of the cylinder liner and piston rings, etc. So, how can we use compressed air to determine the specific faulty part? The method and steps are as follows:
First, turn the piston of the measured cylinder to the compression top dead center.
Then, shift the transmission into a high gear or use the handbrake. If the machine is equipped with a torque converter, a crowbar can be used to pry the starting ring gear to prevent the crankshaft from rotating.
Next, remove the injector and introduce compressed air at a pressure of 0.8MPa through the installation hole.
After that, observe the possible phenomena:
If bubbles emerge in the radiator (water tank) or air leaks from the joint between the cylinder block and the cylinder head, it indicates that the cylinder head gasket is burnt and should be replaced. The burnt cylinder head gasket can lead to the leakage of combustion gas, which not only affects the power output of the engine but also may cause damage to other components due to the leakage of high-temperature and high-pressure gas.
If air leaks from the intake manifold or the exhaust manifold, it means that the valves are not closed properly. In this case, the valves, valve seats should be ground or replaced, or the valve clearance should be readjusted. Improper valve closure can result in incomplete combustion, reduced engine efficiency, and increased fuel consumption.
If there is serious blow-by from the oil filler hole of the oil pan or the dipstick hole, it indicates that there is piston ring blow-by or excessive wear. It may also be due to a broken piston ring, a broken piston ring land, or wear of the cylinder liner. In such a situation, the piston should be taken out for inspection. Piston ring problems can significantly affect the compression ratio of the cylinder, leading to a decrease in engine power.
2. Inspecting Whether the Cylinder Block Has Cracks
After the overhaul of an internal combustion engine or the replacement of the cylinder liner, it is necessary to check whether the cylinder block has cracks, leaks, etc. In the absence of special tooling equipment, using compressed air for inspection is a simple, convenient, and accurate method.
First, make a special cylinder head gasket from a 10mm-thick rubber plate (the same size as three cylinder head gaskets), removing only the bolt holes and cylinder liner holes.
Then, cut a seamless steel pipe with a diameter of 22mm into cylindrical sleeves with a length of 130mm (the number depends on the engine model).
Next, fill the water channel with water, install the self-made rubber cylinder head gasket, and then install the old cylinder head gasket. Put a cylindrical sleeve on each cylinder head bolt and tighten it with a nut.
Finally, input compressed air with a pressure of 0.5 – 0.7MPa from the drain cock on the engine block. Then, observe whether there are any leaks inside and outside the engine block and around the cylinder liner. Cracks in the cylinder block can lead to coolant leakage, which may cause the engine to overheat and damage the engine components.
3. Checking the Performance of a Power Shift Transmission
The performance of a power shift transmission after maintenance can be tested using compressed air before it is installed on the machine.
After assembling the transmission, do not install the shift valve temporarily.
Fill each piston cylinder of the transmission with the allowable oil.
Connect the air pipe to each gear oil passage in turn and input compressed air with a pressure of 0.6 – 0.8MPa. At the moment of ventilation, the movement of the tested piston should be visible, or a “snap” sound should be heard when the piston makes contact. At this time, the output shaft should not be able to rotate. After stopping the ventilation, the piston should be able to return to its original position automatically without any jamming. If the output shaft can rotate, it can be determined that the gear is normal; otherwise, the maintenance of this time is not successful. A malfunctioning power shift transmission can affect the speed change and power transmission of the crane, reducing its work efficiency.
4. Checking the Working Performance of a Hydraulic Motor
The structure of a hydraulic motor is relatively complex, and there are many key points in the assembly process. Slight negligence during the repair process may result in the motor not working or working weakly. If it is installed without performance testing, rework is likely to occur.
Fix the assembled hydraulic motor on the workbench and inject the allowable working oil into the motor.
Input compressed air with a pressure of 0.6 – 0.8MPa from one oil port. The output shaft of the hydraulic motor should rotate at a uniform speed without jamming or surging. When compressed air is input from the other oil port, it should rotate in the opposite direction. In this case, the working performance of the motor can be considered normal. A hydraulic motor with abnormal performance may not be able to provide sufficient power for the crane’s working mechanism, affecting the normal operation of the crane.
5. Investigating the Leakage Parts of Various Radiators (Water Tanks)
First, clean the oil sludge and dust on the surface of the radiator (water tank).
Temporarily block one pipe joint of the radiator (water tank) with a wooden plug.
Immerse the entire radiator in a water tank, leaving only the other pipe joint exposed above the water surface.
Input compressed air with a pressure of 0.3 – 0.5MPa into the radiator (water tank) through the exposed pipe joint.
Observe whether there are any bubbles emerging from various parts of the radiator. If there are, it indicates a leak. Mark the leaking part, take out the radiator, and repair it by welding or patching. A leaking radiator can lead to a decrease in the coolant level, causing the engine to overheat and potentially leading to engine damage.
6. Disassembling a Rusty Caliper Disc Brake
Using compressed air to press out a rusty caliper disc brake is very effective. The method is as follows:
After removing the caliper, tighten the bleeder screw.
Fill the brake with brake fluid from the oil inlet and then input compressed air with a pressure of 0.6 – 0.8MPa to press out the piston.
Since the tightness of each piston may vary, do not rush to remove the piston that is pressed out first. After replenishing the brake fluid, continue to use compressed air to press it out until both pistons can be removed. A rusty caliper disc brake may not be able to provide sufficient braking force, posing a safety hazard to the crane’s operation.
7. Checking the Working Performance of a Pneumatic-hydraulic Master Cylinder
Fix the repaired pneumatic-hydraulic master cylinder on the test bench and install a pressure gauge with a range of 15MPa at the outlet of the air pressure pump.
Fill the fuel tank with brake fluid and discharge the air in the brake pump.
Input compressed air with a pressure of 0.8MPa at the inlet of the air pressure pump and maintain it for 2 minutes.
If the pressure drop of the pressure gauge is not greater than 0.05MPa, there is no leakage, the pointer of the pressure gauge is within the range of 12 – 13MPa, and the air piston can return to its original position quickly, it is considered qualified. An unqualified pneumatic-hydraulic master cylinder may affect the braking performance of the crane, which is crucial for ensuring the safety of the crane during operation.
In conclusion, using compressed air to check the faults of crane-related components is a practical and efficient method. It can help maintenance personnel quickly and accurately identify problems, take timely repair measures, and ensure the normal operation of cranes. At the same time, regular inspection and maintenance of crane components are essential to improve the reliability and safety of cranes and reduce the occurrence of faults and accidents. When using compressed air for inspection, it is necessary to pay attention to safety, follow the correct operation procedures, and ensure that the inspection results are accurate. By mastering this method, maintenance personnel can better serve the crane maintenance work and contribute to the smooth progress of construction projects. Additionally, with the continuous development of crane technology, it is also necessary to continuously explore and innovate inspection methods to adapt to the needs of different types of cranes and improve the overall level of crane maintenance. Regular training and skill improvement of maintenance personnel are also important to ensure the effective implementation of these inspection methods. In the future, more advanced inspection technologies may emerge, but the use of compressed air will still play an important role in crane maintenance due to its simplicity and effectiveness. By combining different inspection methods and technologies, we can better protect the safety and reliability of cranes and promote the healthy development of the construction industry.
