TUBE AS 2186627 - Caterpillar

Illustration 1 g00878409
Brake Control Valve (Parking) (1) Pressure switch (parking brake oil) (2) Actuator oil supply port (3) Parking brake control valve (4) Tank port (5) Accumulator oil pressure
Illustration 2 g00878404
(6) Stem (7) Spring (8) Ball (9) Oil passage for the actuator oil supply port (10) Spool (11) Retainer (12) SpringIf the oil in the brake system is at the normal operating pressure, the parking brake will disengage when the parking brake control knob is pushed inward. Stem (6), spool (10), and retainer (11) move to the right. This allows accumulator oil pressure (5) to be diverted into oil passage (9) to actuator oil supply port (2). The pressure of the oil forces a piston to compress internal springs in the parking brake actuator. The pressure of the oil will overcome the force of the springs in the parking brake actuator. This will cause the parking brake to disengage.Detent springs (7) and detent balls (8) move in and out of grooves that are machined into spool (10). This allows the spool to be in the proper position during engagement of the parking brake or disengagement of the parking brake.When the operator pulls the parking brake control knob outward, the parking brake will engage. Stem (6), spool (10), and retainer (11) move to the left. This blocks the flow of oil from the accumulator. A passage is opened to tank port (4) which allows oil from the actuator to flow to the hydraulic tank. The force of the springs in the actuator will cause the parking brake to engage.If the oil pressure in the brake system is low during machine operation, the parking brake control valve will engage the parking brake. The Caterpillar Monitoring System will indicate a Warning Category 3. If the machine is in first speed FORWARD or if the machine is in first speed REVERSE, the transmission will return to NEUTRAL position.With a loss of hydraulic oil pressure, the force of spring (12) will move retainer (11), spool (10), and stem (6) to the right. This will block any flow of oil that would keep the spring compressed. Oil passage (9) to the tank port is opened in order to allow the actuator to engage the parking brake.If hydraulic pressure is not available to release the parking brake, a drive-through mode is available. This allows the machine to be moved for service. First speed forward or first speed reverse must be used in order to drive through a parking brake that functions correctly.Before the ECM will allow the transmission to shift into a forward speed or into a reverse speed with the parking brake engaged, the parking brake control knob must be pushed inward. Place the direction switch in first speed forward or first speed reverse. The ECM will not allow the transmission to shift. Place the direction switch in the NEUTRAL position. Then place the direction switch in the same direction of travel that was first requested. The second attempt to shift into first gear forward or