Komatsu hydraulic excavators are highly favored in engineering construction due to their efficient and stable performance, with the boom hydraulic system circuit being a key component.
The main function of the boom hydraulic circuit is to provide powerful and precise power support for the boom movement of the excavator. It consists of hydraulic pumps, control valves, hydraulic cylinders, and a series of hydraulic pipelines and other components.
During operation, the hydraulic pump pressurizes the hydraulic oil and delivers it to the control valve. The control valve precisely controls the flow direction and flow rate of hydraulic oil according to the operating instructions, thereby achieving the lifting, lowering, and maintaining of the boom in a specific position.
The design of the hydraulic circuit for the boom of Komatsu hydraulic excavator has many advantages. Its efficient energy transfer efficiency can ensure strong power output while minimizing energy loss to the greatest extent possible. Accurate flow control ensures smooth and accurate movement of the boom, improving the accuracy and efficiency of the operation.
Basic principle of hydraulic circuit for boom:
1. Main circuit: In the above figure, the bold lines and related components together constitute the main circuit. Through this diagram, we can clearly see the specific path of the high-pressure oil output from the main pump to the boom, that is, (main pump → main control valve → boom cylinder). With this diagram, we can quickly and accurately locate the corresponding components on the vehicle body to grasp the situation of the main circuit.
2. Control circuit: The control circuit is relatively complex. The control circuit of the boom is composed of multiple parts, including PPC circuit, pump control circuit, safety circuit, and electrical control circuit.
3. PPC circuit: The key components of the PPC circuit are the boom PPC and the self reducing valve. The pressure of the PPC circuit is between 33-2 kg/cm2, which is provided by the main pump through the self reducing valve, and then distributed through the boom PPC valve to reach both ends of the boom main valve, thereby controlling the opening of the main valve and effectively adjusting the movement speed of the boom.
4. Pump control circuit: The pump control circuit is composed of PC valve, LS valve, LS-EPC valve solenoid valve, PC-EPC solenoid valve, servo piston, and mechanical mechanism inside the pump. The external input signals include PLS pressure generated by driver operation, main pump pressures PP1 and PP2 that reflect external loads, and computer signals that reflect the operation mode. And the output signal is only one, which is the pressure P5 input to the servo piston head. Pressure P5 can directly drive the servo piston to move, thereby controlling the flow rate of the pump. The magnitude of pressure P5 depends on the PLS pressure and the magnitude of PP1 and PP2 pressures.
5. Safety circuit: The safety circuit is composed of a main relief valve, an unloading valve, and a safety oil suction valve. When the pressure of the main pump exceeds 325 kg/cm2, the main relief valve will automatically open to prevent damage to the oil pipes, pumps, cylinders, and control valves in the entire hydraulic system. When the control lever is in a neutral state, the oil output by the pump will flow back to the tank through the unloading valve, which not only reduces energy consumption but also avoids infinite pressure increase caused by the pump output oil having nowhere to go, resulting in damage to components. The function of the safety oil suction valve is that when the boom cylinder encounters sudden external impact, the high pressure inside the cylinder can be relieved to the oil tank through the safety oil suction valve, effectively preventing damage to the cylinder and oil pipe.
6. Electronic control circuit: The combination and combination circuit is mainly based on the actual needs of the operation, according to the operation mode selected by the driver and the operation of the control lever, the computer automatically sends the command of pump diversion or combination to control the pump diversion or combination. The input current of LS-EPC and PC-EPC solenoid valves is also controlled by instructions issued by the computer according to the operating mode.
However, there may also be some issues with the hydraulic circuit of the boom. For example, hydraulic oil leakage may cause a pressure drop, affecting the force and speed of the boom movement. Wear or blockage of hydraulic components can disrupt the normal working order of the circuit and cause abnormal movement of the boom. How to troubleshoot? Mainly from the following aspects: Assuming the diagnostic is oil, it flows along the oil pipe, and as long as it reaches a certain component, there is a possibility of damage to that component.
For example, when the boom is raised, the maximum pressure of the main pump is 230kg/cm2 (other devices are normal)
Main pump: Because there are no issues with other devices, the main pump is functioning properly;
Self reducing valve: Given that other devices are functioning properly, the self reducing valve is also functioning properly;
Main overflow valve: Due to the good working condition of other devices, there is no abnormality in the main overflow valve;
Unloading valve: Since other devices are functioning normally, there is no problem with the unloading valve itself, but the PLS pressure also determines the operation of the unloading valve. In the overflow state, PLS is equal to the main pump pressure. If the PLS pressure is too low, the unloading valve cannot withstand the main pump pressure inside, resulting in the main pump pressure flowing through the unloading valve to the oil tank. Therefore, it is necessary to check the PLS pressure.
Main valve of boom: Has the main valve core moved? (Is it stuck, is the PPC pressure too low)
Safety oil suction valve: It is necessary to check whether the main pump pressure leaks back to the oil tank from the cone valve core or cone part of the safety oil suction valve?
Boom cylinder: To confirm if the main pump pressure is leaking back into the oil tank from the inside of the cylinder?
By using this method, a detailed inspection of every component through which the main oil circuit flows can accurately identify the problem.
Regular maintenance and upkeep are crucial to ensure the normal operation of the boom hydraulic circuit. This includes checking the quality and level of hydraulic oil, promptly replacing worn seals and components, and cleaning hydraulic pipelines.
In short, a deep understanding of the working principle and characteristics of the hydraulic circuit of the Komatsu hydraulic excavator boom is of great significance for ensuring the efficient operation of the excavator, timely troubleshooting, and extending the service life of the equipment.