1. Neutral loop
When the control lever is in the neutral position, the oil pressure of the main pump is blocked by the main sliding plunger in the control valve, and the oil pressure in the circuit increases until the spring force of the unloading valve is broken, and the hydraulic oil flows through the oil return and oil cooler. Return to the hydraulic oil tank, as shown in Figure 2-22.
2. Forearm operation
When the arm is operated, the pilot hydraulic oil of the pilot pump flows into the end of the forearm sliding plunger through the pilot valve, and pushes the forearm sliding plunger to open the system oil circuit, so that the oil flows into the bottom of the forearm cylinder, and the forearm cylinder starts to make the forearm roll. Back to the action.
The return oil of the forearm cylinder flows back to the hydraulic oil tank through the holding valve and the forearm sliding plunger, as shown in Figure 2-23.
3. Rotating circuit
The rotating control rod is opened, the pilot oil pressure pushes the rotating sliding plunger in the control valve, and the rotating motor is opened through the pilot valve to allow hydraulic oil to flow into the system. The pilot oil also flows to the direction solenoid valve to release the parking brake.
The system pressure oil of the main pump is injected into the rotating motor through the rotating sliding plunger, and the rotating motor drives the rotating gear to rotate the upper structure, as shown in Figure 2-24.
4. Combined operation of boom and rotation
When the boom and rotation are combined, the pilot oil of the pilot pump pushes the rotary slide plunger and the boom through the pilot control valve to open the circuit of the two. The system pressure of the main pump simultaneously activates the rotating motor and the boom cylinder through the rotation and boom sliding plunger, as shown in Figure 2-25.
5. Safety circuit
When the cylinder piston is pushed to the top of the stroke, the system oil pressure flows from the Hitachi excavator main pump through the main sliding plunger in the control valve to reach the maximum pressure in the cylinder. At this time, the high-pressure oil of a part of the cylinders overflows, flows through the shuttle valve to the unloading valve, overcomes the spring force and flows back to the hydraulic oil tank, as shown in Figure 2-26.
