Komatsu 830E, Руководство по ремонту

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L07027 Hoist Circuit L7-3
HOIST VALVE
The hoist valve (Figure 7-3) is mounted above the
hoist and steering pump. Hydraulic oil from the high
pressure filters is routed to the hoist valve. The hoist
valve is a split spool design. (The term “split spool”
describes the spool section of the valve.)
Separate spools control oil flow to each end of the
cylinders. The valve consists of two identical inlet
sections, a spool section, and a separator plate.
The hoist valve precisely follows differential pressure
input signals generated by the hoist pilot valve.
(Refer to Figures 7-6 through 7-10.)
The inlet sections of the hoist valve consist of the fol-
lowing components:
• Flow control and main relief valve (system relief).
• Low pressure relief valve.
• Load check poppet.
• Anti-void poppet.
The flow control portion of the flow control and main
relief valve allows pump flow to return directly to tank
through the inlet section with low pressure loss. The
relief portion of the valve is direct acting and has the
capacity to limit the working pressure at full pump
flow.
The low pressure relief is located between the low
pressure core and the outlet, and provides a con-
trolled back pressure in the low pressure core when
oil is returning to tank.
The load check allows free flow from the inlet to the
high pressure core and prevents flow from the high
pressure core to the inlet.
The anti-void check valve allows free flow from the
low pressure core to the high pressure core and pre-
vents flow from the high pressure core to the low
pressure core.
The spool section of the hoist valve consists of the
following components:
• Two pilot ports
• Two main spools
• Two work ports
• Check poppets
The pilot ports are located in the top spool section
cover. These ports provide connections for pilot lines
from the hoist pilot valve. Each pilot port has a corre-
sponding work port.
The work ports provide for line connections between
the spool section and the hoist cylinders. One main
spool for each work port is spring centered at both
ends to close the work port from the high and low
pressure cores when there is no flow to the pilot
ports.
When there is flow through a pilot port to a spool, a
positive differential pressure at the top of the spool
will overcome the bottom spring bias causing the
spool to shift to connect the high pressure core to the
work port. When there is flow from the main valve
work port to the pilot port through the cross-holes, a
positive differential pressure at the bottom of the
spool will overcome the top spring bias and the spool
will shift to connect the work port to the low pressure
core.
The check poppets located in the main spools permit
free flow from the work port to the pilot port and
restrict flow from the pilot port to the work port. These
check poppets control spool response and spool
movements.
FIGURE 7-3. HOIST VALVE
1. Inlet Section
2. Top Spool Section
Cover
3. Down Pilot Port
4. Spool Section
5. Separator Plate
6. Inlet Section
7. Return to Tank Port
8. Supply Inlet port
9. Tie Rod
10. Nut
11. Bottom Spool Cover
12. Head End Work Port
13. Raise Pilot Port
14. Inlet Section Cover
15. Pilot Valve Supply
Port