Float Operation (Figure 7-10) - Komatsu 830E-AC Shop Manual

Float Operation (Figure 7-10)

When the operator releases the lever as the body
travels down, The Hoist Pilot Valve spool returns to
the FLOAT position. In this position all ports (10, 12,
14, & 15) and the Power Down Pilot Line Solenoid
Valve are common with each other. Therefore; the
pilot supply oil is returning to tank with no pressure
buildup thus allowing the Flow Control Valve 2 to
remain open to allow the pump oil to return to the
tank through Hoist Valve Port 10. With no blockage
of either Raise or Down Pilot Ports 14 & 15 in the
Pilot Valve, there is no pressure on the top of either
main spool. The oil returning from the Head End of
the hoist cylinders builds pressure on the bottom of
the Head End Spool 8 exactly like in Power Down
allowing the returning oil to transfer to the Low Pres-
sure Passage 20. The back pressure in the Low
Pressure Passage created by the Low Pressure
Relief Valve 3 causes pressure under the Rod End
Spool 7 to move the spool upward. This connects the
Low Pressure Passage to the Rod End of the hoist
cylinders. The 517 kPa (75 psi) in the Low Pressure
Passage causes oil to flow to the rod end of the cylin-
ders to keep them full of oil as they retract. When the
body reaches the frame and there is no more oil flow
from the cylinders, the Main Spools center them-
selves and close the cylinder ports and the High and
Low Pressure Passages.
L7-16
FIGURE 7-10. HOIST CIRCUIT: FLOAT
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