BASE A. 9B0976 - Caterpillar

Illustration 1 g00878199
Service Brake Control Valve (1) Piston. (2) Spring. (3) Spring. (4) Spring. (5) Retainer. (6) Ball. (7) Spacer. (8) Upper valve spool. (9) Plug. (10) Outlet to rear service brakes. (11) Passage. (12) Drain port to tank. (13) Supply from accumulator for the rear service brakes. (14) Upper valve spool passage. (15) Cavity. (16) Lower valve spool. (17) Outlet to tank. (18) Outlet to front service brakes. (19) Passage. (20) Lower valve spool passage. (21) Supply from accumulator for the front service brakes. (22) Spring. (23) Cavity.Note: The illustration shows the service brake control valve for the 814F Wheel Tractor which is equipped with service brakes on the front axle and the rear axle. The 815F Soil Compactor and the 816F Landfill Compactor are equipped with standard service brakes on the front axle. The service brake control valve for these machines functions in the same way except the valve spool and ports for the rear service brakes are not present.Modulation of the pressurized oil in the accumulators to the service brakes is controlled by the service brake control valve. 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.When the operator pushes on the brake pedal, a roller on the brake pedal assembly forces piston (1) downward. Piston (1) applies a force on springs (2), (3), and (4). The force of the springs moves retainer (5) and ball (6). Movement of the retainer and the ball causes upper valve spool (8) to move away from the seat in spacer (7) .The movement of upper valve spool (8) causes the movement of lower valve spool (16) and the compression of spring (22). When valve spools move, oil flow through passages (11), and (19) to the hydraulic oil tank is blocked.This allows pressurized oil from accumulator ports (13) and (21) to flow through passages (11), (14), (19), and (20). The oil then flows through passages (10) and (18) in order to apply the service brakes. At the same time, pressurized oil flows into cavities (15) and (23), and through passages (14) and (20). The oil pressure at the service brakes has the same pressure as the oil in cavities (15) and (23) .Oil pressure in cavity (23) and the force of spring (22) act to balance lower valve spool (16) against the force of the pressure in cavity (15). In the same manner, pressure in cavity (15) creates a force against the bottom of upper valve spool (8). The upper valve spool is balanced by the force of spring (2) and (3) at the top of spool (8) .The force of springs (2), (3), and (4) is balanced by the force that is applied to the pedal. Upward movement of valve spools (8) and (16) causes accumulator ports (13) and (21) to be covered. The level of pressure in the independent valve sections creates a force of feedback. This allows