For Komatsu PC200-8 Boom relief valve Main gun relief valve

What we're talking about in the main relief valve is when the system pressure goes up a little bit, model six
When the pressure difference between the two ends of the main plunger valve exceeds the function of the soft spring of the main valve, the main plunger valve is lifted, the main valve is opened, the spring is connected to the oil tank, a large amount of oil is throttled through the main valve port, and then flows back to the oil tank through the oil return port, which is the pressure control overflow process. Understanding this principle can understand the working principle of the boom to keep the valve down by analogy.
When the hydraulic excavator arm is lowered, it is important to note that it relies on the PPC valve controlled from the toggle
The guiding pressure oil first pushes the slide valve that controls the main valve (the valve is equivalent to the pilot valve in the pilot relief valve, which moves at this time
The oil in the bottom chamber of the arm returns to the tank through the internal oil hole of the main valve through the path opened by the slide valve. When the pressure oil flow passes through the damping hole of the main valve of the holding valve, the pressure drop is generated, so that the oil pressure acting on the upper and lower ends of the main valve is unequal, forming a certain pressure difference. The main valve is opened, and the pressure oil flowing from the bottom of the boom flows through the main valve to the boom control valve. When there is abnormal high pressure in the bottom circuit of the boom cylinder, the safety valve in the holding valve is opened to play a protective role.