In the hydraulic system of hydraulic excavator, the main relief valve is installed at the upper and lower ends of the main control valve, one at each end. This valve sets the maximum pressure when the entire hydraulic system is working. When the system pressure exceeds the set pressure of the main relief valve, the main relief valve opens the oil circuit of the oil return tank to overflow the hydraulic oil back to the oil tank, so as to protect the entire hydraulic system and avoid excessive pressure in the oil circuit. The main relief valve is mainly used to regulate and limit the system pressure. The main relief valve can effectively protect the hydraulic system from being damaged by changing pressure. Therefore, if the main relief valve fails, it will affect the working efficiency of the excavator and even damage the excavator. This article will explain the causes and solutions of the system pressure fluctuation caused by the failure of the main relief valve for reference only.
1. Causes
① The lock nut is loosened due to the vibration of the screw regulating the pressure, causing pressure fluctuation.
② The hydraulic oil is not clean, and there are tiny dust, which makes the main valve core slide inflexible. Irregular pressure changes may result and the valve may become stuck.
③ The main valve core cannot slide smoothly, which causes the damping hole to be blocked and unblocked.
④ The conical surface of the main valve core and the conical surface of the valve seat are in poor contact and have not been well run in.
⑤ The damping hole of the main valve core is too large to play a damping role.
⑥ The adjusting spring of the pilot valve is bent, resulting in poor contact between the valve core and the cone valve seat and uneven wear.
2. Solutions
① Clean the oil tank and pipeline regularly. Filter the hydraulic oil entering the oil tank and pipeline system.
② If there is a filter in the pipeline, the secondary filter element shall be added. Or replace the filtering accuracy of the secondary element. Disassemble and clean the valve components, and replace the clean hydraulic oil.
③ Repair or replace unqualified parts.
④ Reduce the damping aperture appropriately.
