discharged from the hydraulic hammer to ensure the accelerated drop of the pile
hammer. When the two solenoid reversing valves are in the closed position, the
hydraulic oil returns to the tank and the hydraulic system unloads.
12.1.2 Strike Frequency and Strike Energy
12.1.2.1 Strike Frequency
The strike frequency of hydraulic pile hammer depends on the working time of each
stage of pile hammer. The shorter the working time, the higher the strike frequency
is. Because the falling acceleration of hydraulic pile hammer is usually designed at a
gravitational acceleration or above, the falling time is very short, and the strike
frequency mainly depends on the rising time. During the rising process of single
acting hydraulic hammer, hydraulic pump and high-pressure accumulator supply oil
at the same time, with fast rising speed and high striking frequency, such as CGL370
hydraulic hammer of British BSP Company. When the double acting hydraulic
hammer rises, the hydraulic pump simultaneously supplies oil to the cylinder and the
high-pressure accumulator. The pile hammer rises slowly and the strike frequency is
low, such as the NH hydraulic hammer of Japan Vehicle Company. For Dutch IHC
S-type double acting hydraulic hammer and Finnish JUNTTAN HHKA single acting
hydraulic hammer, in the rising stage, the hydraulic pump and high-pressure accumulator simultaneously supply oil to the lower chamber of the hydraulic cylinder,
with a high strike frequency of 60 beats per minute.
12.1.2.2 Strike Energy
The strike energy is related to the weight of the hammer, the rising height, the
pressure of the oil (or gas) in the upper chamber of the hydraulic cylinder, and the
magnitude of the strike acceleration. When single acting hydraulic hammer drives
piles, the upper chamber of the cylinder is a low-pressure chamber, which is
connected with the return oil circuit. It mainly relies on self-weight to strike the pile
by approximate free falling, and the impact energy is low. Double acting hydraulic
hammer relies on hydraulic pressure or aerodynamic force plus the weight of the
hammer body, which generally has larger impact energy. Table 12.1 compares the
main performances of several typical hydraulic hammers.
12.1.3 Main Characteristics and Parameters
BSP Company, founded in 1905, is the earliest company to develop hydraulic
hammer. Its hydraulic hammer is mainly suitable for steel and concrete piles on
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12 Pneumatic–Hydraulic Pile Driving Hammer
hammer. When the two solenoid reversing valves are in the closed position, the
hydraulic oil returns to the tank and the hydraulic system unloads.
12.1.2 Strike Frequency and Strike Energy
12.1.2.1 Strike Frequency
The strike frequency of hydraulic pile hammer depends on the working time of each
stage of pile hammer. The shorter the working time, the higher the strike frequency
is. Because the falling acceleration of hydraulic pile hammer is usually designed at a
gravitational acceleration or above, the falling time is very short, and the strike
frequency mainly depends on the rising time. During the rising process of single
acting hydraulic hammer, hydraulic pump and high-pressure accumulator supply oil
at the same time, with fast rising speed and high striking frequency, such as CGL370
hydraulic hammer of British BSP Company. When the double acting hydraulic
hammer rises, the hydraulic pump simultaneously supplies oil to the cylinder and the
high-pressure accumulator. The pile hammer rises slowly and the strike frequency is
low, such as the NH hydraulic hammer of Japan Vehicle Company. For Dutch IHC
S-type double acting hydraulic hammer and Finnish JUNTTAN HHKA single acting
hydraulic hammer, in the rising stage, the hydraulic pump and high-pressure accumulator simultaneously supply oil to the lower chamber of the hydraulic cylinder,
with a high strike frequency of 60 beats per minute.
12.1.2.2 Strike Energy
The strike energy is related to the weight of the hammer, the rising height, the
pressure of the oil (or gas) in the upper chamber of the hydraulic cylinder, and the
magnitude of the strike acceleration. When single acting hydraulic hammer drives
piles, the upper chamber of the cylinder is a low-pressure chamber, which is
connected with the return oil circuit. It mainly relies on self-weight to strike the pile
by approximate free falling, and the impact energy is low. Double acting hydraulic
hammer relies on hydraulic pressure or aerodynamic force plus the weight of the
hammer body, which generally has larger impact energy. Table 12.1 compares the
main performances of several typical hydraulic hammers.
12.1.3 Main Characteristics and Parameters
BSP Company, founded in 1905, is the earliest company to develop hydraulic
hammer. Its hydraulic hammer is mainly suitable for steel and concrete piles on
274
12 Pneumatic–Hydraulic Pile Driving Hammer