Komatsu 930E-2 Shop Manual page 453

The secondary low pressure relief is located between
the low pressure core and the outlet to the brake
cooling circuit. It provides for pressure relief if pressure
spikes occur in the low pressure passage area.
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 prevents
flow from the high pressure core to the low pressure
core.
Spool Sections
Work Ports (Rear) Spool Section
The rear spool section of the hoist valve consists of the
following components:
• Pilot ports
• Main spools
• Work ports
• Check poppets
The pilot ports are located in the spool section cover.
These ports provide connections for a pilot line to the
hoist pilot valve. Each work port has a corresponding
pilot port.
The work ports provide for a line connection between
the spool section and the hoist cylinders. One main
spool for each work port is spring biased at both ends
to block the work port from the high and low pressure
cores when there is no flow through the spool cross
holes.
When there is flow through the pilot ports to the spools,
a positive differential pressure at the top of the spool
will overcome the bottom spring bias and the spool will
shift to connect the work port to the high pressure core.
When there is flow from the main valve work port to
the pilot port through the cross-holes, a positive differ-
ential 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 spool section 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
during void conditions.
L07023
Tank Ports (Front) Spool Section
The primary low pressure valves are located in the
front spool section of the hoist valve. These valves
maintain back pressure on the low pressure passage
and direct the hoist cylinder return oil back to the
hydraulic tank.
HOIST PILOT VALVE
The hoist pilot valve (Figure 7-3) is mounted in the
hydraulic components cabinet behind the operator's
cab. The hoist pilot valve spool is spring centered to
the neutral position and is controlled directly by the
operator through a lever mounted on the console
between the operator and passenger seat. A cable
connects the cab mounted lever to the hoist pilot valve
in the hydraulic components cabinet.
When the operator moves the lever, the pilot valve
spool moves and directs pilot flow to the appropriate
pilot port on the hoist valve. The pilot flow causes the
main spool to direct oil flow to the hoist cylinders.
The hoist pilot valve is equipped with a one way load
check valve which allows free flow from the center
passage to bridge core and prevents reverse flow.
The valve also contains the power down relief valve
(2), used to limit power down pressure to 1500 psi
(10.4 MPa).
FIGURE 7-3. HOIST PILOT VALVE
1. Hoist Pilot Valve
2. Relief Valve
3. Supply Port
Hoist Circuit
4. To Hoist Valve (Rod End)
5. To Hoist Valve (Base
End)
L7-3