1.20.1. Tractor Brake Circuit. The tractor brake circuit
consists of the control handles, disc brakes, solenoid
valve, and brake pistons.
The paving machine uses seven steel discs and six
sintered discs for system brakes. With no hydraulic
pressure to the brake system, the brakes are applied by
spring pressure compressing the disc brakes.
The internal charge pump section of the left propulsion
pump supplies hydraulic oil for the brake system. The
hydraulic oil is sent through a charge filter. After passing
through the charge filter, the oil is passed to the brake
system. A tap off is also sent to the test manifold where
brake pressure can be read. The proper pressure in the
brake system is 350 psi (2410 kPa).
The control handles receive electrical power from CB 1.
When either of the control handles is moved from the
center detent position, the control handle produces a 12
VDC signal. Placing the travel switch in the up,
forward/reverse "F/R" position, allows the 12 VDC signal
from the control handles to energize the brake valve
solenoid. The solenoid repositions the brake valve and
passes hydraulic oil to the brake pistons. The piston
overcomes the spring pressure and releases the disc
When the control handles are placed in the center detent
position or the travel switch is placed in the down, neutral
"N" position, power is removed from the brake valve
solenoid. The brake valve repositions and directs the
hydraulic oil from the brake pistons to the return
manifold. The spring inside the brake pistons forces the
hydraulic oil out of the piston and engages the brakes.