PLATE 2728140 - Caterpillar

Illustration 1 g02743057
(1) Plunger
(2) Pilot Supply Port
(3) From Pilot Circuit
(4) Reservoir
(5) Secondary Piston Spring Chamber
(6) To Brake Actuator
(7) Both Released
(8) Primary Piston
(9) Drain Port
(10) Passage
(11) Large Spring Chamber
(12) Compensation Port
(13) One Engaged
(14) From Pilot Circuit
(15) Reservoir
(16) To Brake Actuator
(17) Primary Piston
(18) Feedback Spring Chamber
(19) Check Valve
(20) Secondary Piston
(21) Both Engaged The boosted brake valve group, which uses oil from the pilot accumulator to add boost to the master cylinder.The hydraulic force multiplies the pedal effort so the operator can get more braking force with less effort.The left brake is released (top Illustration) and the right brake (bottom illustration) is engaged. Compensation check valves in the compensation ports are used to equalize the pressures in both brake actuators when the brake pedals are depressed together.With the brake pedal released, the pilot oil is blocked from flowing to the left end of the secondary piston. The pilot oil is also blocked from flowing to the center of the primary piston. The center of the primary piston and feedback spring chamber are also open to tank through the drain port.Oil from the hydraulic tank is connected to the large spring chamber in the middle of the boosted brake group. This oil flows through a passage in the secondary piston. The oil is free to fl ow between the large spring chamber and the secondary piston spring chamber. The check valve in the secondary piston is unseated. The secondary piston spring chamber is connected by lines to the brake actuator.When the brake pedal is depressed, the brake linkage moves the primary piston to the right. Pilot oil is no longer blocked and flows to the left end of the secondary piston, to the center of the primary piston, and to the feedback spring chamber. As pressure increases on the left end of the secondary piston, the pressure assists the primary piston in moving the secondary piston to the right. Pressure sensed in the feedback spring chamber works with the spring to supply feedback or feel to the operator.As the secondary piston moves to the right, the check valve seats, blocking the oil in the secondary piston spring chamber. Oil in the secondary spring chamber is forced out of the chamber to engage the brake. The distance that the brake pedal is depressed determines the amount of oil flow to the brake actuator. The amount of flow determines how fully the brake is applied. The distance the pedal is pushed also determines how much pressure is in the secondary spring chamber and is felt at the brake actuator.Also, as the secondary piston moves to the right, oil fl ows into the compensation ports. When both brakes are applied, both compensation check valves will unseat to equalize the pressure to both brake actuators.When one pedal is depressed, both compensation check valves will move. However, one check valve will seat to block the pressurized oil from entering the other brake cylinder (cutaway view - middle right).When the pedal is released, springs move the secondary piston and