Power Down Operation (Figure 7-9) - Komatsu 830E-AC Shop Manual

Power Down Operation (Figure 7-9)

When the operator moves the lever to lower the
body, the Hoist Pilot Valve is positioned to direct the
pilot supply oil in Ports 12 to Port 15 on the Hoist
Valve to the top of the Rod End Spool 7. Pilot pres-
sure increases to move the spool down compressing
the bottom spring. Movement of the spool connects
the High Pressure Passage 19 to the rod end (annu-
lus area) of the hoist cylinders. At the same time, the
Flow Control Valve 2 is forced to close as pilot pres-
sure increases thus directing the incoming pump oil
to the hoist cylinders through Spool 7 and the over-
center manifold check valve 25 rather than back to
the tank.
If the body is at the maximum up position, the hoist
limit switch has the hoist limit solenoid activated,
closing the raise port 14 on the hoist valve. Power
down pilot pressure in Ports 15 pushes open the pilot
operated check valve 21 so the pilot pressure in
Ports 14 is open to tank through the Pilot Valve
spool. As oil attempts to return from the head end of
the hoist cylinders, it initially encounters the closed
Head End Spool 8. Pressure increases on the bottom
end of the spool causing it to move upward. This
allows the returning oil to go into the Low Pressure
Passage 20, build up 517 kPa (75 psi) to open the
Low Pressure Relief 3, and exit the Hoist Valve
through Port 10 to the tank. As the body descends
and the hoist limit solenoid is no longer activated, the
pilot operated check valve is no longer necessary.
L7-14
FIGURE 7-9. HOIST CIRCUIT: POWER DOWN
1. Hoist Relief Valve 17237 kPa (2500 psi)
2. Flow Control Valve
3. Low Pressure Relief Valve 517 kPa (75 psi)
4. Counterbalance Valve
5. Rod End Work Port
6. Hoist Cylinders
7. Rod End Spool
8. Head End Spool
9. Head End Work Port
10. Return Port
11. Supply Port
12. Pilot Supply Port
13. Power Up Pilot Line Solenoid Valve
14. Raise Pilot Port
15. Down Pilot Port
16. Power Down Relief Valve, 10342 kPa (1500 psi)
17. Anti-void Check Valve
18. Load Check Valve
19. High Pressure Passage
20. Low Pressure Passage
21. Pilot Operated Check Valve
22. Manifold Power Up Port
23. Manifold Power Down Port
24. Solenoid Valve Return Port
25. Overcenter Manifold Check Valve (CV)
Hoist Circuit
POSITION
L07034