Komatsu 830E, Shop Manual

Page: 438 / 783

L4-12 Steering Circuit L04037
BLEED DOWN MANIFOLD
The bleed down manifold (10, Figure 4-7) is located
on the inside of the left hand frame rail just behind
the flow amplifier (6).
The bleed down manifold is equipped with two bleed
down solenoid valves (1), two relief valves (5 & 9), a
low steering pressure switch (4), and pilot operated
check valve (13). The bleed down manifold receives
oil from a high pressure filter. Oil within the bleed
down manifold is directed to the accumulators, brake
circuit, and flow amplifier. Oil supply for the steering
control valve and steering cylinders is supplied by
the flow amplifier.
If for any reason the steering pump supply is lost, the
truck can be slaved from another truck by using the
quick disconnects. Connect “disabled truck” lines to
the quick disconnect fittings located on the outside of
the left frame rail, by the steering accumulators. Also
connect a jumper hose between the quick discon-
nects (2), one located on the bleeddown manifold,
the other just inside the left frame rail by the disabled
truck quick disconnect. This jumper hose must
capable of withstanding 3500 psi (24 MPa) brake
system pressure.
The relief valves, accumulator bleed down sole-
noids, and steering pressure switch are not individu-
ally rebuildable and are factory preset. Refer to
“Steering Circuit Check-Out Procedure” for relief
valve setting.
Each time the keyswitch is turned “Off”, it energizes
the bleed down solenoids. When the bleed down
solenoids are energized, all hydraulic steering pres-
sure, including the accumulator, is bled back to the
hydraulic tank. Brake pressure however, will not
bleed down due to internal check valves in the brake
manifold.
After approximately 90 seconds, the solenoids will
de-energize to close the return port to tank. By this
time all the oil in the accumulator should be returned
to tank. At start-up, the steering circuit will be
charged, including the brake circuit. The Low Steer-
ing Pressure light and buzzer will turn on until steer-
ing pressure reaches 2300 psi (15 858 kPa). This is
controlled by the steering pressure switch located on
the bleed down manifold. During operation, if steer-
ing pressure falls below 2300 psi (15 858 kPa), the
Low Steering Pressure warning light will illuminate.
1. Bleed Down Solenoid
2. Brake Quick
Disconnect
3. Accumulator Supply
4. Low Steering Pressure
Switch
5. Return Relief Valve
(500 psi)
6. Flow Amplifier
7. Unloader Valve Line
8. Check Valve
9. Relief Valve (4000 psi)
10. Bleed Down Manifold
11. Return Line
12. From Steering Filter
13. Check Valve (Piloted)
14. Outlet to Flow Amplifier
15. Hoist Pilot Valve Return
Line
16. Supply to Brakes
17. Return from Flow
Amplifier
FIGURE 4-7.