THEORY OF OPERATION - CONTINUED
General. The propel system allows the roller to move either forward or backward. When the engine is started, oil under
pressure oil from the charge (control) circuit flows to the propel control valves. When the propel control lever (which is
connected to the propel control valves) is in the forward or reverse position, oil is sent to the propel hydraulic pump. The
further the lever is pushed, the higher the oil pressure sent to the hydraulic pump. The more pressure there is, the faster
the roller will move. The hydraulic pump pushes oil through hydraulic lines until the oil enters the propel motors. The
front and rear propel motors turn the propel gearboxes which turn the roller drums. Inside each propel gearbox is a
brake. This brake is always engaged unless pressure from the brake/shift manifold is present. This pressure is controlled
by the propel control valve.
If the roller needs to move while the engine is not able to supply the pump with power, there is a manual brake release
pump on the roller. This manual brake release pump pressurizes the hydraulic lines releasing the brakes. Also, there are
brake and neutral start relays in the system which prevent movement of the roller during the starting procedure.
Fuel/Hydraulic Oil Tank. The fuel/hydraulic oil tank consists of the hydraulic tank (located on the right-side) and the
fuel tank (located on the right-side). Although the tanks are welded together, they are separate in their function. The
CB534B Roller hydraulic oil tank holds 15.5 gal. (59 l) of hydraulic oil. The CB534C Roller hydraulic oil tank holds 24
gal. (91 l) of hydraulic oil.
Propel Hydraulic Pump. The propel hydraulic pump is a variable displacement, piston-type pump mounted in tandem
with the vibratory hydraulic pump to the engine. Both run at engine speed and rotate clockwise as seen from the drive
end of the pump.
Propel Motors. The hydraulic propel motors are located on the left-side of the front drum and the right-side of the rear
drum. The front motors is a fixed displacement axial piston-type motor. The rear motor is a variable displacement axial
Propel Control Lever and Valve. The propel control lever controls the direction of the roller. If the lever is pushed for-
ward, the control valve, which is connected to the lever, directs fluid to the propel hydraulic pump in such a way that the
hydraulic pump sends oil to the propel motor to turn forward. This propel pump sends fluid the opposite direction if the
control lever is pulled backward. The further the lever is pulled, the higher the oil pressure being sent from the control
valve is. The more control valve pressure, the more volume of fluid the pump sends to the motors and the faster the
Parking Brake Switch. The parking brake switch keeps the roller from moving by interrupting the inputs from the con-
trol valve. The hydraulic pump will not send oil to the motors that the brake will not disengage while the parking brake
is on. The parking brake switch glows red when parking brake is engaged.
Brake and Neutral Start Relays.The brake and neutral
start relays are safety devices that interrupt the electrical signal
to the starter if the control lever is not in the neutral, or center position. This ensures that the roller will not move while
the engine is being started.
Steering Pump. The steering pump provides a charge pressure to the propel system. This charge pressure sends source
pressure to the brake/shift valves. The charge pressure is used to supply the propel control valve with signal oil, and to
disengage the brakes.
Brake/Shift Valves. The brake/shift valves distribute the charge pressure to the propel control valve and the brakes.
When pressure is sent from the control valve, the brake/shift valve sends pressure to release the brakes. The brake/shift
valves also control the speed range of the roller operates. The operator controls the speed range by an electrical switch
that operates the valve solenoid. This solenoid either opens or closes the brake/shift valve changing the fluid pressure to
the propel control valve which effectively changes the speed range.
Manual Brake Release Pump. The manual brake release pump is a manually operated plunger-type pump that forces
hydraulic oil to the brakes. The manual brake release pump is used when normal means of brake disengagement are not
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 hydraulic oil in the return side of the closed loop circuit to be
directed to the oil cooler.