compressed nitrogen and its own gravity. When the hammer body descends to the
lowest stroke, it hits the pile head. The hydraulic circuit in the descending stage is
shown in Fig. 12.6.
In this process, the pump 10 still supplies oil to the system. First, it fills the
high-pressure accumulator with oil, so that the high-pressure accumulator can reach
the predetermined initial working pressure for use in the next cycle, and then the
excess high-pressure oil flows back to the tank through the relief valve. In the
pressure-retaining stage, in order to prevent the hammer body from bouncing back
after the strike action is completed, the reversing valves 6 and 8 are closed at the
same time, so that the hammer body stays on the pile for a period of time. After the
pressure-retaining stage, the reversing valve 8 is opened, the reversing valve 6 is
still closed, and the system enters the next working cycle.
12.2.1.2 Dynamics Model of Rising Process
In the rising stage, high-pressure oil is supplied by hydraulic pump, and the flow
equation is satisfied.
Q P ¼ Q R þ Q A þ Q C
ð12:1Þ
where
Q P Pump output flow;
Q R Overflow discharge flow;
Fig. 12.6 Hydraulic circuit of hydraulic–pneumatic pile driving hammer in descending process
12.2 High-Speed Pneumatic–Hydraulic Composite Hammer
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