action of pile hammer impacting the pile head is completed, it enters the
pressure-retaining stage. After pressure holding, the electromagnetic directional
valve 9 is energized and a new working cycle is started.
12.1.1.2 Finnish JUNTTAN Single Acting Hydraulic Hammer
JUNTTAN Finland produces a single acting hydraulic hammer. Figure 12.3 shows
the hydraulic system and outline of HHKA hydraulic hammer. During the rising
stage of pile hammer, the electromagnetic reversing valve 6 is electrified, and the
upper part works, while the main reversing valve 7 lower part works. At this time,
variable displacement pump 1 and high-pressure accumulator 5 simultaneously
supply oil to the lower chamber of hydraulic cylinder 8. The piston rod accelerates
to rise and drives the hammer head to rise. The hydraulic cylinder 8 upper chamber
hydraulic oil flows into the low-pressure accumulator 9 return tank.
In the descending stage of pile hammer, when the pile hammer reaches the
height set by the system, the lower position of electromagnetic reversing valve 6
works. At this time, the upper position of main reversing valve 7 is controlled.
High-pressure oil flows into the upper chamber of hydraulic cylinder 8, forming a
differential circuit, and the pile hammer drops accelerated.
Pressure retention stage of pile hammer. In order to prevent pile rebound, the pile
hammer stays on the pile for a very short period of time, that is, the holding time.
After the pressure retention, the electromagnetic reversing valve 6 moves to make
the main reversing valve 7 change direction, and the pile hammer starts to rise and
Fig. 12.3 Finnish JUNTTAN single acting hydraulic hammer. a HHKA hydraulic hammer
hydraulic system diagram; b HHKA hydraulic hammer profile diagram (1—Variable displacement
pump; 2—Relief valve; 3—One-way valve; 4—Unloading valve; 5—High-pressure accumulator;
6—Electromagnetic reversing valve; 7—Main reversing valve; 8—Hydraulic cylinder;
9—Low-pressure accumulator)
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12 Pneumatic–Hydraulic Pile Driving Hammer