992G Wheel Loader and 854G Wheel Dozer Braking System Brake Control Valve (Parking) Caterpillar

Brake Control Valve (Parking)

Illustration 1g01065649

Location of the Parking Brake Control Valve

Illustration 2g00103057

Parking Brake Control Valve

The parking brake control valve is located under the cab on the left side of the frame. The parking brake control valve controls the flow of pressure oil to the parking brake and from the parking brake.

Illustration 3g00103058

(1) Parking brake control knob.

Illustration 4g00103059

Parking Brake Control Valve

Engaged Position

(2) Pressure port from the brake accumulators. (3) Stem for the parking brake control valve. (4) Spring. (5) Spool. (6) Tank port. (7) Spool. (8) Parking brake port. (9) Retainer. (10) Spring.

When parking brake control knob (1) is pushed in, the parking brake is in the disengaged position. Spool (7) and retainer (9) move to the right. This movement compresses spring (10) and pressure oil is allowed to flow into the pressure port from accumulators (2). The pressure oil also flows into a cavity in the parking brake.

When the pressure of the oil in the cavity is high enough to compress the springs in the parking brake, the brake disengages. This oil pressure keeps the parking brake disengaged.

To engage the parking brake, pull out on parking brake control knob (1). When stem (3) is pulled out, the flow of oil from the accumulators to the parking brake stops. Moving stem (3) causes spool (7) to move to the left. This stops the supply of oil from the accumulators. The oil is then allowed to drain back to the hydraulic oil tank.

This causes a decrease in the oil pressure for the brake system. When the oil pressure is decreased, the force of the springs in the parking brake is greater than the pressure of the oil in the cavity of the parking brake. This allows the springs in the parking brake to engage the parking brake.

If there is an oil pressure drop in the braking system during machine operation, the parking brake control valve automatically engages the parking brake.

With a loss of oil pressure, the force of the springs in the parking brake moves spool (5) to the right. This blocks any flow of oil that would normally help to keep spring (10) compressed. This causes spring retainer (9), spool (7), and stem (3) to move out.

Illustration 5g00103065

(11) Alert indicator. (12) Action lamp. (13) Message area.

When the oil pressure for the parking brake drops below 6035 ± 515 kPa (875 ± 75 psi), the monitoring system alerts the operator. Alert indicator (11) and action lamp (12) will flash. Also, the action alarm will sound. Additionally, message area (13) shows "P BRK ACUM PRESS LO" and "PARKBK ON".

The transmission returns to neutral if the transmission is in first speed forward or in first speed reverse.