Common Faults and Maintenance Methods of the Hydraulic System of Truck cranes

The working pressure of the hydraulic system is generally 20 to 25 MPa. The common faults of hydraulic pumps are leakage at the shaft extension or reduced displacement due to wear. Whether it is a gear pump or a plunger pump, 80% of the internal leakage is caused by the wear of the axial sealing surface, which can be solved by grinding. The faults of hydraulic cylinders are mostly manifested as external leakage or internal leakage. After the piston rod of the hydraulic cylinder is scratched, the seal at the cylinder head is quickly worn out and leaks. When the guide sleeve is worn out of alignment and loses its roundness, if the roundness error exceeds 0.20mm, it will also lead to leakage. The aging of seals is also one of the reasons for external leakage. When repairing a hydraulic cylinder, in addition to replacing the sealing parts, special attention should also be paid to the wear of the support ring on the piston. When the wear is large, it should be replaced. In case of emergency handling, a thin pad can be placed between the support ring and the piston to prevent direct contact between the piston and the cylinder barrel, which may cause cylinder pulling. To prevent the cylinder barrel from being scratched, the support ring and guide sleeve are best made of non-metallic materials. In contrast, piston rods are easier to handle. If it is a large area of roughening, the piston rod can be ground smooth on an external cylindrical grinding machine and then coated with 0.05mm thick hard chromium. Its diameter may be reduced by nearly 1mm. At this point, the thickness of the guide sleeve can be increased accordingly. Even if the structural dimensions of the remaining part of the cylinder head remain unchanged, it will still have a very good sealing effect. If it is a local scratch or the hardened layer peeling off, ordinary carbon steel electrodes can be used to fill and weld the damaged area. The specific approach is: First, dry the welding rods; When welding, intermittent spot welding is adopted, with each spot welding time being 1 to 1.5 seconds. The arc length should be controlled appropriately to avoid "undercut". After welding, just grind it flat and smooth. When the entire machine suddenly stops moving or moves slowly, the first step should be to listen for any abnormal sounds at the pump and power take-off, and check if the oil level in the hydraulic oil tank is normal. After ruling out these easily identifiable causes, it can basically be confirmed that the problem lies with the pressure regulating valve. In this case, do not blindly tighten the pressure regulating screw of the pressure regulating valve. Instead, disassemble the pressure regulating valve for inspection to check if the pilot valve spring is broken, if the pilot valve seal has failed, and if the main valve core is stuck. Special attention should be paid to whether the damping hole of the main valve core is blocked. To prevent excessive pressure from causing damage to the system, the screw should be loosened a little first, and then adjusted from low to high to the specified pressure. Atlas air compressor parts. The balance valve is an important component to ensure the safe operation of truck cranes. If the piston rod of the luffing cylinder or telescopic cylinder extends outward normally, but there is a continuous and slow retraction of the piston rod when the multi-way valve is in the neutral position, it can generally be determined that the balance valve seal is unreliable. If, under load conditions, the piston rod of the hydraulic cylinder has a reference price retraction and is accompanied by a "click, click" sound, there are two possibilities: one is that there is air in the rod cavity of the hydraulic cylinder. Due to the compressibility and elasticity of air, the balance valve opens intermittently. The second issue is that the rodless chamber of the hydraulic cylinder is poorly sealed, causing pressure oil to leak through the piston into the rodless chamber and gradually accumulate. When a certain pressure is reached, the balance valve opens. Sometimes, you may encounter a situation where the piston rod cannot retract. At this time, you can focus on checking whether the damping small holes on the control oil circuit of the balance valve are blocked and whether the plunger is stuck. If the small hole is not blocked and the plunger is not stuck, the small hole can be appropriately enlarged to reduce its throttling effect and compensate for the internal leakage caused by the wear of the plunger and the valve hole. Only in this way can sufficient pressure be generated to push the plunger and open the check valve, allowing oil to return to the rodless cavity. Some medium and small-sized truck cranes use rotary valves to control the individual actions of each vertical outrigger. When the rotary valve has been in use for a long time and the clearance increases, a "bias pressure" will be generated on the valve core, making it quite difficult for the valve core to rotate. Due to the structural limitations of the rotary valve, the valve cores generally do not have pressure equalization grooves. If the problem of difficult rotation is to be fundamentally solved, new parts can only be replaced. The faults of multi-way valves with outriggers and other working mechanisms are mostly external leakage. One of the reasons for external leakage is that the O-rings at both ends of the valve hole are aged, deformed or worn. The second issue is that the exposed part of the valve stem is rusted, damaging the sealing surface. The solution is to replace the O-ring with one that is of appropriate size and specification and smooth and intact. If the end of the valve stem is severely rusted, the rusted part can be ground off, then copper welding can be carried out to restore the original diameter and smooth it. If the hydraulic oil leaks at the joint surfaces of the valve blocks of the multi-way valve, the multi-way valve should be disassembled and the O-rings replaced. When installing, the tightening torque of the connecting screw should be appropriate. If it is tightened too much, the valve stem will not return to its original position flexibly. When the tightening torque is insufficient, leakage is prone to occur again.