THEORY OF OPERATION - CONTINUED
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 range.
The vibratory system is a hydrostatic, closed loop system. Oil for the vibratory system is supplied by the steering
charge circuit pressure created by the steering pump. Charge pressure is used to supply the control circuit and
replenish the main closed loop and cooling circuits of the vibratory system.
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.
Vibratory Hydraulic Motor. The vibratory hydraulic 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 identical.
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 direction, 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
Vibratory Indicators. The vibratory indicators allow the operator to monitor the vibratory system. A vibratory sensor is
located on each drum and measures how many Vibrations Per Minute (VPM) the drums produce. This sensor is con-
nected 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.
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.
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.
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.