If the bulldozer does not lift the blade during normal operation, how can we quickly analyze the cause and dispose of it in time?

　　Taking a D375A-5 bulldozer as an example, when the normal operating temperature rises to 60 degrees, the blade does not rise or rises slowly, the blade no-load high idle speed rises to the maximum height for 6 seconds, and the ground idle speed rises to the maximum The height time is 26 seconds. At the same time, the temperature of the hydraulic system rises faster. After a period of shutdown, the temperature will rise again and the fault will appear again. The slow or weak rise of the blade indicates that the pressure oil flow is reduced and accompanied by pressure loss, the reasons include:

　　1: The main hydraulic pump leaks (internal or external leakage), the main control valve and the pilot control valve wear out of limits, the wear between the hydraulic cylinder piston and the cylinder tube exceeds the limit, there is a leak in the pipeline connection, the main overflow pressure decreases or The main relief valve is damaged. Such troubleshooting methods are as follows: first test the main overflow pressure in the system, the test temperature range is 45-55 degrees, if the lowest pressure at low idle speed is greater than 18.6MPa, the minimum pressure at high idle speed is greater than 19.6MPa, indicating the main overflow pressure of the system The working pressure of the main working pump is normal. When the engine speed is 2200r/min, the flow of the main pump should be 266L/min. At this time, the main pump works normally, otherwise the main pump should be replaced or the main overflow pressure should be adjusted.

　　2: Test the output pressure of pilot oil. When the temperature is 45-55 degrees, if the minimum pressure is 4.46MPa, it indicates that the working pressure is normal. At this time, the flow rate of the pilot pump can be tested. The minimum flow rate of the pilot pump should be 39L/min, otherwise the pilot pump should be replaced.

　　3: Test the settlement of the lifting cylinder. Raise the blade to about 400mm, the test temperature is 45-55 degrees, the settling within 15min should not be greater than 400min, otherwise the lifting cylinder should be replaced.

　　In addition: the following situations may also cause the bulldozer blade to lift weakly

　　1: The hydraulic oil is deteriorated and there are many impurities, which causes the pipeline to be blocked or the oil pressure does not meet the working requirements. The cleanliness of the transmission medium is effective and is the basis for the normal operation of the system. The deterioration of hydraulic oil not only makes the system pressure not meet the requirements, but also corrodes the sealing components and damages the parts.

　　2; The oil seal in the cylinder fails, causing system pressure to leak out.

　　3; The spool of the distribution valve is stuck, so that the system oil flows back from the neutral position to the tank.

　　4: The overflow valve is normally open, and the working oil flows from the overflow valve back to the oil tank.

　　5: The hydraulic pump fails, resulting in an excessively low output pressure.