HOSE AS 3N4906 - Caterpillar

Disengaged
Illustration 1 g00880536
Parking brake (parking brake disengaged) (1) Spring (2) Orifice (3) Port (4) Port (5) Orifice (6) Spring (7) Spring (8) Check valve (9) Plunger (10) Port (11) Port (12) Plunger throttle (13) Check valve (14) SpringOil from the pump enters port (3) of the brake valve through the control valve. The oil flows through check valve (8) to port (10) of the travel motor. The travel motor attempts to rotate. However, return oil from the travel motor flows from port (11) to the brake valve. The pressure of the oil that is entering the pump increases, because the oil is blocked by check valve (13) .Oil that has increased in port (3) acts on the end face of plunger (9) through orifice (2). The oil attempts to shift the plunger to the right. The force that is required to shift the plunger is proportional to the force that is created by spring (6) .When the pressure in port (3) reaches a certain pressure, plunger (9) begins to move to the right. Then, the oil in port (11) goes back to the hydraulic tank. As the oil pressure in the pump increases, the opening rate in the plunger also increases. As a result, the back pressure in port (3) becomes small. The opening rate is automatically adjusted and the travel motor rotates at a speed that corresponds to the pressure of the oil and the flow of the oil in port (3) .Engaged
Illustration 2 g00880594
Parking brake (parking brake engaged) (1) Spring (2) Orifice (3) Port (4) Port (5) Orifice (6) Spring (7) Spring (8) Check valve (9) Plunger (10) Port (11) Port (12) Plunger throttle (13) Check valve (14) SpringWhen the operator moves the control lever to the NEUTRAL position, pump oil is blocked and spring (6) attempts to return plunger (9) to the neutral position. This is due to equal pressures in port (3) and port (4). When plunger (9) is shifted, the opening rate in plunger (9) decreases. However, the travel motor is attempting to rotate because of the inertia load on the machine. Therefore, the pressure in port (11) increases. As a result, the speed of plunger (9) is reduced, because the oil in the pilot pressure chamber passes through orifice (2). With this movement, the speed of the plunger is controlled and the shock load is absorbed. Also, the movement stops the travel motor without creating cavitation.