Komatsu 830E-AC, Shop Manual

Page: 734 / 1085

L7-10 Hoist Circuit L07034
Power Up Operation (Figure 7-7)
The Hoist Pilot Valve spool is moved to the Power Up
position when the operator moves the lever in the
cab. The pilot supply oil coming in Port 12 is pre-
vented from returning to the tank and, instead, is
directed out Port 14 through hoist limit solenoid 13
and into Port 14 of the Hoist Valve. There it goes to
the top of the Head End Spool 8, builds pressure on
the end of the spool, causes the spool to move down
compressing the bottom spring, and connects the
High Pressure Passage 19 to Head End Port 9.
Working oil flow in the High Pressure Passage is now
allowed to flow through the spool and out Port 9 to
extend the hoist cylinders. Even though a small
amount of oil flows through the check poppet in the
top of Spool 8, raise pilot pressure at Ports 14
increases to slightly higher pressure than the
required hoist cylinder pressure. As a result, the pilot
supply pressure in Ports 12 also increases causing
back pressure to occur in the spring area of Flow
Control Valve 2. This overcomes the pilot pressure
on the other end of the Flow Control Valve causing it
to close and direct the incoming pump oil through
Head End Spool 8 to the hoist cylinders to extend
them.
If at any time the resistance to the flow of the pump
oil coming into the inlet section causes the pressure
to increase to 17237 kPa (2500 psi), the pilot pres-
sure against Hoist Relief Valve 1 causes it to open
and allow flow to exit out Port 10 and return to the
tank.
As the hoist cylinders extend, oil in the annulus area
of the second and third stages must exit from the cyl-
inders. Initially, the Rod End Spool 7 ports are
closed. As the returning oil entering Port 5 builds low
pressure, it flows through the check-poppet in the top
of the spool, through Port 15, through the Pilot Valve
spool, and out Port 10 of the Pilot Valve to the tank.
No pressure is present on the top of Spool 7. Cylin-
der return pressure passes through the check-poppet
in the bottom of Spool 7 to build pressure under the
spool which moves the spool upward compressing
the top spring. This movement allows the returning
cylinder oil to flow into the Low Pressure Passage 20
to the Low Pressure Relief Valve 3. Approximately
517 kPa (75 psi) causes this valve to open, allowing
the oil to flow out Port 10 to the tank.
The counterbalance valve 4 will open as the body is
raised and close as the operator releases the hoist
lever and the raise pressure at port 22 decreases. If
the load were to stick near the tail of the body and the
body is overcenter, pressure in the annulus area of
the hoist cylinders will increase.
If the pressure exceeds 20684 kPa (3000 psi) at port
23, the counterbalance valve will open again to direct
oil back to the hoist valve, preventing damage to the
hoist cylinder seals from excessive pressure.
When the operator releases the lever, the valves
change to the HOLD position. If the body raises to
the position that activates the hoist limit switch
located above the right rear suspension before the
operator releases the lever, the Hoist Limit Solenoid
13 is energized. The solenoid valve closes the raise
pilot Port 14 on the hoist and releases the Hoist Pilot
Valve raise pilot pressure at Port 24 to tank, allowing
the Head End Spool 8 to center and shut off supply
of oil to the hoist cylinders. This prevents maximum
extension of the hoist cylinders.
FIGURE 7-7. HOIST CIRCUIT: POWER UP
POSITION
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)