I. Start-up phase
The hydraulic oil flows through the check valve to the accumulator, the pressure control valve, the main spool and the bottom of the piston. The spring force keeps the pressure control valve closed, thus preventing the oil from returning to the tank from the upper part of the piston and preventing the piston from moving. The pressure in the circuit increases, compressing the nitrogen in the accumulator. Note: The top of the piston is always vented to atmosphere.
Second, the acceleration phase of the return stroke
At the start of the piston return stroke, the piston has finished its last shock and is in a transient state of standstill. At this point the main valve V2 cavity is a low pressure cavity, while the V4 cavity is a normal high pressure cavity, so the main spool is in the lower limit position. Thus, the piston front cavity V1 through the main valve spool and high pressure oil, while the piston rear cavity V3 has been connected with the return cavity, for low pressure, so the piston in the front cavity under the action of high pressure oil, for return acceleration movement, while compressing the tail nitrogen chamber nitrogen, so that the adiabatic compression.
Third, the return stage
When the piston finishes impacting, the main spool control end returns to the tank and moves to the left to start the next lifting ring. Note: The oil under the upper piston flange acts as a hydraulic brake for the piston.
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