The set pressure of the hydraulic system is 30MPa, and a pressure lower than this indicates a low system pressure. The faults of the hydraulic system are mainly manifested in two aspects: slow and weak lifting of the boom; Slow and weak rotation. The main cause of the two faults is the low working oil pressure, while the main reasons for the low pressure are blockage and leakage. A smooth and well sealed oil circuit is a guarantee for the normal operation of the system, and blockage and leakage are the most common hydraulic transmission faults. Therefore, checking hydraulic transmission faults generally starts from the hydraulic oil circuit aspect. The following are the diagnosis and troubleshooting methods for different fault phenomena in the hydraulic system.

 

1. The lifting of the boom is slow and weak, while other movements are normal

 

1.1 Fault diagnosis

 

In the hydraulic system, if the lifting of the boom is slow and weak, and the turning of the bucket is normal. It is not difficult to see from the working principle diagram that other functions are normal, which indicates that the working pump and main safety valve are working normally, and the pressure they provide to the entire system is sufficient. At the same time, it also indicates that the pipeline and oil filter at the inlet end of the pump, as well as the oil quantity and quality of the oil tank, are not affected. At this point, all you need to do is check the boom spool valve, boom cylinder, oil pipes in the boom section, and their seals.

 

(1) Check for blockage in the oil circuit

 

Perform routine treatment first, remove the oil pipe, remove the boom spool valve body, valve stem, and related components for cleaning, clean the oil passage, and blow dry with compressed air.

 

(2) Check for oil circuit leaks

 

Leaks in hydraulic systems generally occur after a period of use. From the surface phenomenon, it is mostly caused by seal failure, damage, extrusion, or sealing surface pulling. The main reasons include: oil pollution, improper roughness of the sealing surface, unqualified sealing grooves, loose pipe joints, increased clearance between mating parts, high oil temperature, deterioration or poor assembly of the sealing ring, etc. Leakage is divided into internal leakage and external leakage, and usually faults are mainly caused by internal leakage

 

(3) Handling of internal leakage faults

 

The internal leakage in this section is mainly caused by the leakage in the boom spool valve and cylinder. Internal leakage mainly occurs inside the valve body and cylinder, making it difficult to inspect. But we can use some auxiliary methods to determine the leakage situation.

 

(4) Inspection of the boom oil cylinder

 

After the piston of the boom oil cylinder is retracted to the bottom, remove the rod free oil pipe to continue filling the rod chamber of the boom oil cylinder. If there is a large amount of working oil leaking from the oil pipe port without a rod cavity, it indicates that the hydraulic cylinder has internal leakage; It can also make the bucket full of load, lift it to the limit position, place the boom control lever in the middle position, and turn off the engine to observe the sinking speed of the boom; Then, place the boom control lever in the raised position. If the sinking speed of the boom significantly increases at this time, it also indicates that internal leakage occurred in the hydraulic cylinder; If the change in sinking speed is not significant, the cause of internal leakage is in the boom spool valve.

 

(5) Inspection of the boom spool valve

 

The leakage of the large arm spool valve is mainly due to the large fit gap between the valve stem and valve body, damage to the pressure regulating spring, and damage to the sealing components inside the valve. Check the fit clearance between the valve stem and valve body, check the pressure spring, and check if the sealing parts inside the valve body are damaged.

 

1.2 Exclusion methods

 

If the leakage test results in the cylinder exceed the specified value, it should be disassembled for further inspection. If the sealing ring is damaged, it should be replaced. If the cylinder wall is severely strained, it should be replaced; If the boom valve is severely worn, replace it.

 

2.1 Fault diagnosis

 

In the hydraulic system, if the boom is working normally; The small arm (bucket) operates slowly and weakly. It is not difficult to see from the working principle diagram that the boom lifting is normal, which indicates that the working pump and main safety valve are working normally. At the same time, it also indicates that the pipeline and oil filter at the inlet end of the pump, as well as the oil quantity and quality of the fuel tank, are not affected. At this point, only pay attention to checking the working spool valve, safety valve, and its seals of the small arm (bucket).

 

2.2 Exclusion methods

 

The diagnosis and troubleshooting methods for hydraulic transmission faults are similar, and the troubleshooting methods for the small arm (bucket) and large arm parts are also basically the same. Therefore, this can be used as a reference for dealing with faults in the working part of the small arm (bucket).