①Boom lifting operation.
As shown in Figure 1-36, the boom lifting operation is faster because the oil that originally flowed directly into the oil port P2 is merged and flows into the casing of the pump P1 through the oil port P1. This confluence is supplied to the top of the boom cylinder. At low speed operation, only the spool of the boom 1 works, and the spool of the boom 1 is provided by the hydraulic oil of the pump P2.
The hydraulic oil of the pump P2 flows into the spool of the boom 1 through the oil port P2 and the parallel channel. The hydraulic oil of the pump Pl flows into the spool of the boom 2 through the oil port Pl and the parallel passage.
In the boom lifting operation, the pressure of the pilot control valve enters the port XAbl, and the spool 3 of the left boom 1 moves close to the spring. The hydraulic oil of the pump P2 enters the parallel channel, and then flows through the load check valve LCb1, the boom 1 spool and the check valve HV, then flows into the oil port Abl, and then flows into the top of the boom cylinder.
At the same time, the pilot pressure at port XAb2 pushes the spool 12 of the boom 2 to the left against the two springs. The hydraulic oil of the pump Pl flows through the parallel channel and the central bypass channel 14, and then passes through the load check valve CSP, the boom 2 spool and the load check valve CCb, and then merges the flow into the passage and flows directly into the oil port Abl and the boom The top of the cylinder.
The rod end oil quantity of the boom cylinder returns to the spool of the boom 1 through the port Bbl. Then, it directly flows into the oil return port R2 through the channel.
②Modern excavator boom lowering operation.
As shown in Figure 1-37, during the boom lowering process, the pressure of the pilot control rod is supplied to ports XBb1 and BbL, and the spool 3 of the boom 1 moves to the right against the two springs 7 and 8 inside and outside.
The hydraulic oil of the pump P2 enters the parallel channel through the load check valve LCb1 and flows directly into the oil port Bbl, and then flows into the rod end of the boom cylinder.
The return flow from the top of the boom cylinder flows back to the boom 1 spool through port Abl, and then directly enters the return channel R2 through the channel.
In addition, limiting the return oil flow in the channel lowers the boom cylinder at an appropriate speed.
