1.20.1. Tractor Brake Circuit

TM 5-3895-373-20 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 brakes. 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. 1-38