a. The drum vibration is produced by the turning of an eccentric weight mounted inside each drum.
Hydraulic motors, mounted on the left-side of the axis of the front drum and on the right-side of the
axis of the rear drum, turn the eccentric weights. A hydraulic pump provides power to the motors.
Controls are provided for the operator to implement the use of the vibratory system in high or low
b. The vibratory system is a hydrostatic, closed loop system. Oil for the vibratory system is supplied
by the steering change circuit pressure created by the steering pump. Charged pressure is used to
supply the control circuit and replenish the main closed loop and cooling circuits of the vibratory
2. Vibratory Hydraulic Pump. The vibratory hydraulic pump is a variable displacement, piston-type pump
mounted in tandem with the propel hydraulic pump to the engine. Both run at engine speed and rotate
clockwise as seen from the drive end of the pump.
3. Vibratory Hydraulic Motor. The vibratory motors are located on the right-side of the front drum and the
left-side of the rear drum. The front and rear motors are fixed displacement bidirectional motors that are
4. Eccentric Weights. As the eccentric weight spins, kinetic energy creates forces that cause the drum to
vibrate, which intensifies the roller compaction of surface material. The eccentric weight is a chamber filled
with steel shot and has a weight attached to one side. Inside the chamber are baffles. As the weight is turned
one direction, the baffle collects the steel shot on the same side as the weight to produce a severe imbalance
in the rotation. The imbalance causes the entire drum to vibrate. This is the high amplitude range. As the
weight is turned the other director, the baffle collects the steel shot on the opposite side as the weight to
produce a mild imbalance in the rotation causing less vibration. This is the low amplitude range.
5. Vibratory Indicators. The vibratory indicators allows the operator to monitor the vibratory system. A
vibratory sensor is located on each drum and measures how many Vibrations Per Minute (VPM) the drum
produce. This sensor is connected to a VPM meter on the control panel. The VPM meter points to a number
which shows the vibrations per minute reading. A system light is also illuminated whenever the vibratory
system is engaged.
6. Brake/Shift Manifold Valve. The brake/shift manifold valve will not allow the vibratory system to engage
when the system is in automatic mode until the propel lever is positioned for roller movement.
7. Cooling Valve. The cooling valve is a two-position pilot operated valve. Pilot oil from the high pressure side
of the closed loop circuit opens the valve allowing some of the oil in the return side of the closed loop circuit
to be directed to the oil cooler.
8. Hydraulic Oil Cooler. The hydraulic oil cooler is mounted between the fan shroud and the radiator and is
a heat transfer device which cools the oil in the hydraulic system.