Dawson EMV-300 Operator's Instructions/Spare Parts List page 8

3.0 HOW DOES THE EXCAVATOR MOUNTED VIBRATOR WORK?
Modern pile vibrators basically work in the same way. Pairs of high-speed contra-rotating
eccentric weights are geared together so as to produce net vertical vibratory forces.
The vibrations produced are transmitted to the pile through a powerful hydraulic grip.
Consequently the pile is vibrated at the same speed and displacement (or movement) as the gearbox
itself. This vibration effect is transmitted to the pile tip where the surrounding soils become almost
fluid like.
The fluidising effect on the soil permits particles to shuffle themselves around creating some spaces
for the pile to move into. This combined with the weight of the pile and vibrator is adequate to
push the pile into the ground.
Not all soil types will however fluidise. Clays soils are very cohesive and extremely dense by
comparison to sands and gravels where vibrators work best. The dense clay soil does not allow soil
particles to shuffle themselves around so no fluidising effect can occur. Also the ground effectively
sticks itself to the pile and much of the power generated is lost in shaking the ground.
The EMV is particularly effective for its size and weight because it is able to utilise the crowd force
available from the excavator to add further push force to the pile.
The gearbox in the EMV unit is driven by a hydraulic drive motor that receives hydraulic power
from the excavators bucket ram circuit. Typically this circuit will be able to supply adequate
working pressure but excessive amount of oil flow rate. The EMV has a built-in flow regulator that
limits the oil flow rate supplied to the drive motor so that the gearbox can not be run too fast. This
is essential to prevent excessive bearing loads and correct performance of the unit.
In addition, the flow regulator has a sequence valve built-in that will not allow the vibrator to run
until adequate clamping force has been applied to the pile – an essential safety feature. This
simplified hydraulic system enables simple installation and reliable performance.
Hydraulic
Drive Motor
Flow Regulator
and Sequence
Valve
Saddle
Assembly
with Swivel
Gearbox
containing
eccentric
weights
Transport
Stand