TUBE 7N5123 - Caterpillar

Brake Control Valve
Illustration 1 g06076175
(1) Brake Pedal ValveBrake pedal control valve (1) is on the front right side, beneath the operators platform.A mechanical link connects the two brake pedals to each other. When a brake pedal is depressed, a lever and cam assembly actuates the service brake control valve. The control valve is a fully split modulating valve with two independent output pressures.
Illustration 2 g06076664
Visual representation showing the relationship between input force and brake pressure
The service brake control valve modulates the flow of pressurized oil. The flow of pressurized oil is modulated between the brake accumulator and the service brakes. The position of either brake pedal causes a specific pressure at the service brakes. As the position of the pedal changes, the pressure at the service brakes also changes.
Illustration 3 g06076240
Service brake control valve with brakes engaged
(A) Brake Port
(B) Pressure Port
(C) Tank Port
Illustration 4 g06076242
Service brake control valve with brakes Released
(A) Brake Port
(B) Pressure Port
(C) Tank PortWhen one of the brake pedals is depressed, a roller in the brake pedal assembly pushes down on the piston compressing the spring. The force of springs causes the upper valve spool to move away from the seat in spacer.The movement of upper valve spool causes the movement of lower valve spool and the compression of the spring. When valve spools and move, the oil flow through passages to the hydraulic oil tank is blocked allowing pressurized oil from the accumulator to flow through the passages. The oil then flows through passages to apply the service brakes.The force of springs is balanced by the force that is applied to the pedal. Upward movement of valve spools causes accumulator ports to be covered. The level of pressure in the independent valve sections creates a force of feedback. This feedback allows the operator to modulate the pressure to the service brakes.Valve spools balance between the ports for the hydraulic oil tank and the ports for the service brakes. These spools maintain the brake pressure until the position of the pedal changes. The change in the pedal position means that more brake pressure or less brake pressure is necessary.If the piston is moved downward to apply more compression on spring , valve spools will move. The valve spools move to allow more pressure oil to flow to outlets and to the service brakes. This results in a higher oil pressure in cavities. Higher oil pressure is necessary to maintain the balance of valve spools .