PLATFORM GP 3591072 - Caterpillar

Components
A. Charge Valve
The charge pump is part of the left-hand propel pump (as seen from the left side of the machine). It provides charge oil to the front drum propel system and to the secondary/parking brakes.The charge pump is located in the engine compartment on the left side of the machine.B. Brake Valve
Oil from the charge pump is routed directly to the brake valve. The brake valve is a two-position solenoid valve, which determines whether the secondary/parking brakes are engaged or released. When the solenoid is de-energized, the brakes are engaged, holding the machine in place. When the solenoid is energized, the brakes are released, allowing the machine to move.C. Pressure Switch
This normally-closed pressure switch is installed in the pressure line between the brake valve and the brakes. It monitors oil pressure to the parking brakes, and is wired to the brake lamp/buzzer.D. Secondary/Parking Brakes
The system uses two identical parking brakes - one at the front drum and one at the rear drum. Each parking brake is a spring-applied, hydraulically-released type, which is connected to a drum drive gearbox on the left side of the machine.When the brakes are engaged, the front and rear drum drive gearboxes are prevented from turning. This holds the machine in place. When the brakes are released, the gearboxes can operate freely. This lets the machine move in forward or reverse.E. Brake Switch
The brake switch is an electrical toggle switch, which is located on the instrument panel. The brake switch is wired directly to the solenoid valve. The operator uses the brake switch to engage or release the brake.F. Brake Lamp/Buzzer
The brake lamp/buzzer is located on the instrument panel at the operator's console. When the brake is engaged, the lamp will be lighted and the buzzer will sound. When the brake is released, the lamp will be dark and the buzzer will be silent.Operation
Secondary/Parking Brake Components
(1) Hydraulic oil tank. (2) Return hose. (3) Pressure switch. (4) Brake valve. (5) Charge pump. (6) Front parking brake. (7) Hose. (8) Hose. (9) Rear parking brake.Parking Brake "Engaged"
1. Hydraulic oil from charge pump (5) (part of the propel system) is routed to brake valve (4). The pressure of this charge oil will be approximately 2070 kPa (300 psi).Reference: For more information on the charge pump, see Propel Systems Operation Testing and Adjusting, Form No. KENR1551.2. Because the brake switch (on instrument panel) is ON, the solenoid in brake valve (4) is de-energized. Hydraulic oil from charge pump (5) is blocked at brake valve (4), and is not routed to brakes (6) and (9).3. Any oil pressure at brakes (6) and (9) drains through hoses (7) and (8) to pressure switch (3) and brake valve (4). This oil is ported through brake valve (4) to return hose (2), and is routed back to hydraulic oil tank (1). For more information on oil flow through brake valve (4), see Brake Valve, located in this module.4. With pressure drained, the spring-loaded brakes (6) and (9) apply braking force to