Komatsu Galeo PC138US-8 Shop Manual page 208

SEN02550-01
Function
This valve reduces the swing back generation
q
in the swing body by the inertia of the swing
body, the backlash and rigidity of the machin-
ery system, and the compression of the
hydraulic oil when the swing is stopped.
The valve contributes in preventing collapsing
q
of load when the swing is stopped and also
contributes in reducing cycle time (enhances
the positioning performance, enabling you to
proceed to the next work quicker than ever).
Operation
1. When port (MB) brake pressure is generated
Pressure (MB) is conducted to chamber (d) via
q
notch (g).
The pressure compresses spring (6) by use of
q
the difference in areas of circles (øD1 > øD2)
of spool (5) and moves spool (5) to the left
side.
Port (MB) o chamber (e) will be intercon-
q
nected.
Since pressure (MA) is lower than the set pres-
q
sure of spring (3), spool (2) does not move and
the pressurized oil is kept in. Thus the braking
force is ensured.
26
10 Structure, function and maintenance standard
2. When motor is stopped temporarily
The motor rotation is reversed by the closing
q
pressure generated at port (MB). (1st time:
reverse rotation)
Reversing pressure is generated on port (MA).
q
Pressure (MA) is conducted to chamber (a).
The pressure compresses spring (3) by use of
q
the difference in areas of circles (øD3 > øD4)
of spool (2) and moves spool (2) to the right
side.
Port (MA) o chamber (b) will be intercon-
q
nected.
Ports (b) and (f) will be interconnected through
q
the drilled hole (h) on spool (5). This intercon-
nection bypasses the reversing pressure on
port (MA) to port (T), thereby preventing the
reverse rotation of the 2nd time.
PC138US, USLC-8