(2) In the dropping process of hydraulic hammer, the pressure equation between
the hydraulic oil from hydraulic cylinder, reversing valve, low-pressure accumulator and return pipeline is as follows.
p d ¼ p L þ Dp 2 ; p L ¼ Dp 1
ð12:39Þ
where
Dp 1 Pressure drop of return pipeline;
Dp 2 Pressure drop of reversing valve;
p L
Pressure of low-pressure accumulator.
(3) Low-pressure accumulator plays different roles in different stages of hydraulic
hammer. In the rising stage, the absorbed hydraulic oil is flowed back to the
tank through the return pipeline by the low-pressure accumulator. In the inertia
rising stage, the low-pressure accumulator supplies hydraulic oil to the
hydraulic hammer through a one-way valve to prevent suction. In the
descending stage, the low-pressure accumulator absorbs oil from the lower
chamber of the hydraulic hammer, so that the hammer body can descend
rapidly. In the pressure-retaining stage, the absorbed hydraulic oil is flowed
back to the tank through the return pipeline by the low-pressure accumulator.
The accumulator should be as close as possible to the hydraulic hammer. Due
to the short drop time of hydraulic hammer, the variable process of gas in
accumulator satisfies the following equation:
p 0 V
n
0 ¼ p 1 V
n
1 ¼ p L V
n
L
ð12:40Þ
where
p 0
Charging pressure of accumulator;
p 1
Maximum working pressure of accumulator;
p L
Working pressure of accumulator at a certain moment;
V 0 ; V 1 ; V L Accumulator gas volume under three different pressures;
n
Gas Variability Index. Because of the short working time, it can be
regarded as adiabatic condition, taking n ¼ 1:4.
The flow rate of low-pressure accumulator can be obtained by derivative both
sides of Eq. (12.40).
Q a ¼
dV L
dt
¼ À
V L
np L
dp L
dt
ð12:41Þ
12.4 Rapid Piling Process of High-Speed Pneumatic–Hydraulic Composite Hammer
301