①Forearm extension operation.
When the arm is extended, the pressure of the pilot control valve is supplied to the pilot ports (XBal and XBa2), and the arm 1 spool 9 is moved to the left against the springs 4 and 5, and the arm 2 spool 1 is moved to the left to tighten Rely on inner and outer springs 2, 3. The hydraulic oil of the pump Pl flows through the load check valve LCal, the lock-down valve HV and the parallel passage, and then directly enters the rod end of the forearm cylinder through the oil port Bal.
At the same time, the pilot pressure of port XBa2 moves the spool 1 of the forearm 2 to the left side against the inner and outer springs 2 and 3. The hydraulic oil of the pump P2 flows into the parallel passage and the central bypass pipe, and then flows through the check valve of the boom priority valve and the spool 1 of the small arm 2. After the oil volume is combined, it flows directly into the oil port Bal and the rod end of the forearm cylinder.
The flow at the top of the arm cylinder flows back to the spool 9 of the arm 1 through the oil port Aal, and then flows directly to the oil return port R2 through the channel.
②Modern excavator arm retracting operation.
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 and abuts against the inner and outer springs 4 and 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 forearm is retracted, the hydraulic oil of the pump P1 flows into the spool 9 of the forearm 1 through the parallel passage. Then, enter the top of the forearm cylinder through the load check valve LCal, the check valve HV and the oil 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 boom priority valve and the oil port Aal. The backflow at the rod end of the forearm cylinder is pressurized due to the forearm's own weight or related reasons.
The pressurized oil flows back to the oil port Bal and enters the forearm 1 through the outside of the spool 9 of the forearm 1. Only when the load is light, the pressurized oil pushes open the check valve of the valve body, and fills the parallel passage from the opposite direction of the hole (c) on the valve core, and enters the oil port Aal. This process is the forearm regeneration function.
When the pressure at the top of the forearm cylinder increases, the plunger (d) and the sub-spool (e) move to the right. At the same time, the valve body check valve (f) at the rod end of the forearm cylinder is input through the oil hole (b) on the periphery of the spool The oil flows to port Bal, and then returns to the hydraulic tank through tank port R2.
