At the beginning of the return stroke of the piston, the last impact of the piston was over, and it was in a state of transient pause. At this time, the main valve V2 cavity is a low pressure cavity, and the V4 cavity is a normal high pressure cavity, so the main valve core is at the lower limit position. In this way, the front cavity V1 of the piston communicates with the high-pressure oil through the main valve core, and the rear cavity V3 of the piston is always in communication with the return oil chamber, which is a low pressure. Therefore, the piston accelerates the return stroke under the action of the high-pressure oil in the front cavity and compresses the nitrogen at the tail Chamber nitrogen for adiabatic compression.
The piston continues to make upward movement under the action of high-pressure oil. When the lower side of the piston crosses the lower side of the control port, the high-pressure oil in the V1 cavity enters the V2 cavity of the main valve. Due to the hydraulic pressure acting on the main spool through the V2 cavity The hydraulic pressure of the chamber larger than V4 acts on the main spool, thereby forcing the spool to start a reversing movement. The movement of the valve core gradually reduces the high-pressure oil entering the V1 cavity, so that the corresponding return thrust on the piston is gradually reduced, and the return resistance exerted by the compressed nitrogen is increasing, and the piston is turned into the return Braking phase. The spool will eventually be completely shut off to the pressure oil in the V1 cavity, and the piston will soon stop returning.