Bleeddown Manifold Valve; Bleeddown Solenoid; Bleeddown Manifold - Komatsu 930E-2 Shop Manual

BLEEDDOWN MANIFOLD VALVE

The bleeddown manifold valve (4, Figure 4-1) is located
on the inside of the left hand frame rail just behind the
flow amplifier. The bleeddown manifold is equipped
with the following major circuit components as shown
in Figure 4-3:
• Steering Pressure Switch (6)
• Steering accumulator bleeddown solenoid valve
(7)
• 600 psi (4.1 MPa) Relief Valve (12)
• 4000 psi (28.0 MPa) relief valve (13)
• Body-Up Solenoid Valve (15)
• Pilot operated check valves (see Figure 4-4)
The bleeddown manifold receives oil from the steer-
ing/brake pump through a high pressure filter and
directs oil to the accumulators, brake circuit, flow am-
plifier and autolube system hydraulic pump. Oil supply
for the steering control unit and steering cylinders is
supplied via the flow amplifier. The manifold also pro-
vides hoist circuit control when the body is raised.
The relief valves, accumulator bleed down solenoid,
and body-up limit solenoid are factory preset and not
individually rebuildable.

Bleeddown Solenoid

Each time the keyswitch is turned OFF, with the truck
stopped, it energizes the steering system bleed down
solenoid (7, Figure 4-3 & 27, Figure 4-4). When the
bleed down solenoid is energized, all hydraulic steer-
ing pressure, including the accumulators, is bled back
to the hydraulic tank. Brake pressure however, will not
bleed down due to internal check valves in the brake
manifold and bleeddown manifold check valve (see
schematic).
After approximately 90 seconds, the solenoid will de-
energize to close the return port to tank. By this time
all the oil in the accumulators should be returned to
tank. At start-up, the steering circuit will be charged,
including the brake circuit. The Low Steering Pressure
light and buzzer will turn on until steering pressure
reaches 2300 psi (15.9 MPa). This is controlled by the
steering pressure switch (6, Figure 4-3).
During operation, if steering pressure falls below 2300
psi (15.9 MPa), the Low Steering Pressure warning light
will illuminate until pressure returns to normal.
L04031
FIGURE 4-3. BLEEDDOWN MANIFOLD
1. To Hoist Valve, Power Up
2. To Hoist Valve, Power Down
3. Spare Pressure Port
4. Test Port
5. To Brake System
6. Steering System Pressure Switch
7. Steering Accumulator Bleed Solenoid
8. Supply To Flow Amp
9. Return From Flow Amp
10. To Front Steering Accumulator
11. To Rear Steering Accumulator
12. Relief Valve, 600 psi (4.1 MPa)
13. Relief Valve, 4000 psi (28.0 MPa)
14. Autolube Pump Supply Port
15. Hoist Up Solenoid Valve
16. Return From Hoist Pilot Valve
17. Hoist Pilot Valve, Power Down
18. Hoist Pilot Valve, Power Up
19. Return to Tank
20. Feedback Pressure to Unloader valve
21. Supply From Pump
Steering Circuit L4-3