SEAL- 2389634 - Caterpillar

The Secondary Brake Air Control Valve Is In The ON Position.
Illustration 4 g01202766
The engine is operating. The parking brake reset valve is closed. The parking brake control valve is in the OFF position. The secondary brake air control valve is in the ON position. (16) Secondary air tank (17) Parking and secondary brake valve (18) Secondary brake and parking brake pressure switch (19) Parking brake control valve (20) Secondary brake air control valve (21) Secondary brake inverter valve (22) Parking brake reset valveNote: The darkened lines show air pressure and the arrows show the direction of flow.Note: Secondary brake and parking brake pressure switch (18) is activated when the secondary brake air control valve is in the ON position.Air pressure from secondary air tank (16) flows to the secondary brake air control valve (20) and through the parking brake reset valve (22) to the secondary brake inverter valve (21) . When the pedal for secondary brake air control valve (20) is partially depressed to the ON position, a portion of the full supply pressure is sent to the control passage of the secondary brake inverter valve (21) . Secondary brake inverter valve (21) will block some of the air pressure that is flowing to the parking and secondary brake valve (17) . The result is modulated secondary braking action.When the pedal on secondary brake air control valve (20) is held in the full ON position, air pressure from secondary air tank (16) flows through the secondary brake air control valve to the control passage of the secondary brake inverter valve (21) . The secondary brake inverter valve blocks all of the air pressure that was flowing to the parking and secondary brake valve (17) . The parking brakes are applied by springs and the parking brakes are released by pressure. When the air flow to parking and secondary brake valve (17) is blocked, the oil pressure to the brake housing will be blocked and the springs will apply the parking brakes.When you release the pedal for the secondary brake air control valve (20) , the pedal is returned by a spring to the OFF position. When the secondary brake valve is in the OFF position, air is not sent to the control passage of the secondary brake inverter valve (21) . Secondary brake inverter valve (21) allows air pressure from secondary air tank (16) to flow to parking and secondary brake valve (17) . This air flow will cause parking and secondary brake control valve (17) to send oil to the brake housing. The oil pressure will release the parking brakes.The Service Brake Air Control Valve Is In The ON Position
Illustration 5 g01202876
The engine is operating. The parking brake reset valve is closed. The parking brake control valve is in the OFF position. The secondary brake air control valve is in the OFF position. The service brake air control valve is in the ON position. (2) Primary air tank (16) Secondary air tank (18) Secondary brake and parking brake pressure