CYLINDER AS 1144776 - Caterpillar

Illustration 1 g06111531
Service Brake Control Valve
The service brake control valve is on the front left side, and underneath the operator 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 g00274835
Service Brake Control Valve
(B) Service brake ports. (C) Pressure ports.
Illustration 3 g00910322
View A-A of the Service Brake Control Valve
(1) Piston. (2) Spring. (3) Spring. (4) Retainer. (5) Ball. (6) Spacer. (7) Upper valve spool. (8) Outlet to rear service brakes. (9) Outlet to hydraulic oil tank. (10) Passage. (11) Supply from accumulator for the rear service brakes. (12) Drain port to tank. (13) Upper valve spool passage. (14) Cavity. (15) Lower valve spool. (16) Plug. (17) Outlet to front service brakes. (18) Passage. (19) Lower valve spool passage. (20) Supply from accumulator for the front service brakes. (21) Cavity. (22) Spring.
The service brake control valve modulates the flow of pressurized oil between the brake accumulators 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.When a brake pedal is depressed, piston (1) applies a force on springs (2) and (3). The force of springs (2) and (3) moves retainer (4) and ball (5). Movement of retainer (4) and ball (5) causes upper valve spool (7) to move away from the seat in spacer (6).The movement of upper valve spool (7) causes the movement of lower valve spool (15) and the compression of spring (22). When valve spools (7) and (15) move, oil flow through passages (10), (12), and (18) to the hydraulic oil tank is blocked.This restriction allows pressurized oil from accumulator ports (11) and (20) to flow through passages (10), (13), (18), and (19). The oil then flows through passages (8) and (17) to apply the service brakes. At the same time, pressurized oil flows into cavities (14) and (21), and through passages (13) and (19). The oil pressure at the service brakes has the same pressure as the oil in cavities (14) and (21).Oil pressure in cavity (21) and the force of spring (22) act to balance lower valve spool (15) against the pressure in cavity (14). In the same manner, pressure in cavity (14) creates a force against the bottom of upper valve spool (7). The upper valve spool is balanced by the force of spring (2) at the top of spool (7).The force of springs (2) and (3) is balanced by the force that is applied to the pedal. Upward movement of valve spools (7) and (15) causes accumulator ports (11) and (20) to be covered. The level of pressure in the independent valve sections creates a force of feedback. This pressure allows the operator to modulate the pressure to the service brakes.Valve spools (7) and (15) balance between the ports