1. Characteristics of rotary hydraulic circuit
1. Function of U-type spool valve
Due to the large rotational inertia of the slewing mechanism, in order to prevent excessive peak pressure from the slewing drive oil circuit, its directional valve generally functions as a U-shaped spool valve, forming two parallel sealing belts in the working state, so the spool valve The effect of wear on leakage is greater than other types of spool valves.
2. M-direction charge limiting circuit
In order to avoid the inertial rotation of the vehicle, the low-pressure side generates a high degree of vacuum, which causes gas to be precipitated in the hydraulic oil. The two working oil circuits are equipped with a replenishment valve to ensure the stability of the circuit. Because the two working oil circuits are completely symmetrical, so Two plug-in pilot pressure limiting valves are set to limit the maximum working pressure of the two branches.
2. Reasons for sluggishness
The cause of hydraulic failure should be analyzed and checked from the entire system. The reasons for the weak rotation of the excavator may be:
The wear of the R pump motor and directional valve, the return resistance is too large, the slewing mechanism movement resistance is too large, and the servo control pressure is too low. However, the most likely causes are the following two aspects:
1. Wear of the charge valve
Due to the frequent opening and closing of the charge valve, there will be squeezing deformation and wear between the valve seat and the valve core. The wear form is similar to the valve cone surface of the engine, and the wear of the valve core cone surface is the main. The seat will cause the leakage of the circuit in the non-refueling state (that is, the driving state) to decrease, and the working pressure oil will leak from the replenishing valve, resulting in weak or even unable to rotate.
2. The damping hole of the pressure limiting valve is blocked
Generally, the set pressure of the rotary oil circuit is lower than other pressures of the system, which is mainly related to the rated pressure of the hydraulic motor, and is also far lower than the rated pressure of the main pump, so the pressure limiting valve of the rotary oil circuit is often opened. The frequent opening of the pressure limiting valve will cause the wear of the valve core and the valve sleeve on the one hand, and on the other hand, the impurities in the oil will cause the blockage of the valve core damping hole. After the damping hole is blocked, the opening pressure of the pressure limiting valve is completely determined by the preload of the return spring of the main valve core. The preload force can only meet the friction force and hydraulic force of the valve core, and cannot drive the rotary motor.
3. Trouble shooting
1. Check the fault
First check the working condition of the hydraulic main pump. In the state of boom raising at full speed, observe the degree of load of the engine, mainly based on the sound of the engine and the color of the exhaust gas. If the load level can reach more than 2/3 of the rated power, the main pump works normally. Then operate the slewing device, if the engine load is very low, and the slewing speed is very slow, or even cannot rotate, it can be preliminarily determined that it is the fault of the charge valve and the pressure limiting valve.
2. Trouble shooting
Dismantle the charge valve and pressure limiting valve. If the wear amount of the charge valve core is less than 0.3mm, the valve core can be flattened with the original taper with a cylindrical grinder, or it can be flattened with a thin set knife on a drilling machine or lathe. polishing. When assembling, an appropriate gasket can be placed on one end of the valve core spring as required. If the wear is more than 0.3mm, the charge valve needs to be replaced. The pressure limiting valve mainly depends on the wear of the pilot valve. The emergency excavator can also use the grinding method when repairing, and replace it if necessary. The pressure-limiting valve must use the light transmission method to check whether the damping hole is smooth. If it is not smooth, it should be blown through with compressed air. When assembling, if there is no pressure measuring device on site, the adjustment bolt can be left 1~2 buckle outside the lock nut. After assembly, it can be adjusted appropriately according to the operation situation. ,
According to the grinding condition of the valve core, it can be considered that the low hardness of the valve core is the main reason for the premature wear of the valve core. It is recommended that the design department appropriately increase the surface hardness of the valve core and improve the material of the valve core.
The three excavators repaired by the above method did not have any problems of weak rotation after hundreds of hours of use, which ensured the normal operation of the excavator.
