① Arm out operation.
As shown in Figure 1-38, when the arm is extended, the pressure of the pilot control valve is supplied to the pilot port (XBal and XBa2), and the spool 9 of the arm 1 is moved to the left against the springs 4 and 5. The arm 2 spool 1 moves to the left against the inner and outer springs 2 and 3. The hydraulic oil of the pump Pl flows through the load check valve LCal, the lock-down valve HV and the parallel channel, and then directly enters the rod end of the arm cylinder through the oil port Bal.
At the same time, the pilot pressure of port XBa2 moves the spool 1 of the arm 2 to the left against the inner and outer springs 2 and 3. The hydraulic oil of the pump P2 flows into the parallel channel and the central bypass pipe, and then flows through the check valve of the priority valve of the boom and the spool 1 of the arm 2. After the oil volume is combined, it flows directly into the oil port Bal and the rod end of the arm cylinder.
The flow from the top of the arm cylinder returns to the spool 9 of the arm 1 through the port Aal, and then flows directly to the oil return port R2 through the channel.
②Modern excavator arm retraction operation.
Only in light load as shown in Figure 1-39.
The pressure increase at the top of the arm cylinder is shown in Figure 1-40.
When the arm is retracted, the pressure of the pilot control valve is supplied to the ports XAal, XAa2 and BaL. The spool 9 of the arm 1 moves to the right next to the inner and outer springs 4, 5, and the spool 1 of the arm 2 moves to the right Move close to the inner and outer springs 2, 3.
When the arm is retracted, the hydraulic oil of the pump Pl flows into the spool 9 of the arm 1 through the parallel channel. Then, it enters the top of the arm cylinder through the load check valve LCal, check valve HV, and port Aal.
At the same time, the hydraulic oil of pump P2 flows into the spool 1 of the arm 2 through the parallel channel, and then enters the top of the arm cylinder through the check valve of the arm priority valve and the oil port Aal. The return flow at the rod end of the arm is pressurized due to the weight of the arm or related reasons.
The pressurized oil flows back to the oil port Bal and enters the arm 1 through the outside of the spool 9 of the arm 1. Only at light load, the pressurized oil pushes the valve check valve open, and the reverse connection from the hole (c) on the spool fills the parallel channel into the oil port Aal. This process is the regeneration function of the forearm.
When the pressure on the top of the arm cylinder increases, the plunger (d) and the sub-spool (e) move to the right, and at the same time, the body check valve (f) on the rod end of the arm cylinder enters through the oil hole (b) on the periphery of the valve core The oil flows to the oil port Bal, and then returns to the hydraulic oil tank through the oil tank oil port R2.
