Komatsu 830E-AC Shop Manual page 557

BRAKE VALVE
The brake valve is a pressure modulating valve,
actuated mechanically (brake pedal) or hydraulically
through the automatic apply valve (12, Figure 3-1).
The Brake Valve independently controls the pressure
delivered to the front and rear service brake assem-
blies. Apply pressure can be modulated from zero to
maximum braking effort by use of the foot pedal.
Rebuild Criteria
If any one of the following conditions exist, the brake
valve should be removed and repaired:
• Excessive cam rock in pedal actuator.
• Any sign of external leakage.
• Internal leakage at the tank port must be less
than 100 cc/minute with the valve in the released
position and system pressure supplied to the
"P1" and "P2" inlet ports.
• Tank port leakage must be less than 250 cc/
minute with valve pilot or manual applied at 20
685 kPa (3,000 psi) system pressure.
• Failure of the pedal to return to full release
position.
• Valve holds pressure when in the neutral
position.
• Varying output pressure with the pedal fully
depressed.
Removal
If the Brake Valve is to be removed from the vehicle
for repair or adjustment, additional equipment will be
required as outlined in disassembly, assembly.
NOTE: Minor repairs and service adjustment may not
require the removal of the brake valve.
Before disconnecting pressure lines, replacing
components in the hydraulic circuits, or install-
ing test gauges, always bleed down hydraulic
steering and brake accumulators. The steering
accumulators can be bled down with engine shut
down, turning the key switch OFF and waiting 90
seconds. Confirm the steering pressure is
released by turning the steering wheel - No front
wheel movement should occur. Open bleed down
valves (10 & 12, Figure 3-1) located on the brake
manifold and allow both accumulators to bleed
down.
J03034
BRAKE CIRCUIT COMPONENT SERVICE
Brake Circuit Component Service
FIGURE 3-1. ACCUMULATORS AND BRAKE
MANIFOLD
1. Rear Brake Accumulator
2. Charging Valve
3. Front Brake Accumulator
4. Charging Valve
5. Brake Lock Shuttle Valve
6. Brake Lock Pressure Reducing Valve (PR1)
7. Park Brake Reducing Valve (PR2)
8. Brake Lock Solenoid
9. Park Brake Solenoid
10. Park Brake Test Port
11. Bleed Down Valve (Front Brake Accumulator)
12. Automatic Apply Valve
13. Bleed Down Valve (Rear Brake Accumulator)
14. Accumulator Test Port (LAP1)
15. Brake Manifold
16. Low Brake Accumulator Pressure Switch
17. Park Brake Pressure Switch
J3-3