SANY LATIN AMERICA
4-104
SY195/205/215/225C9 Crawler Hydraulic Excavator
Structure and Function
Shop Manual - June 2013
2) Safety valve
Function
●
When the machine travel is stopped (or it
is travelling downhill), the counterbalance
valve closes the inlet and outlet circuits of
the motor. Since the motor is rotated by
inertial force, pressure in the motor outlet
port side is abnormally increased, poten-
tially resulting in damages on the motor
and piping. The safety valve releases this
abnormal pressure to the inlet port side of
the motor in order to prevent damages to
the equipment.
Operation
1. When travel is stopped (or when travelling
downhill) (Right swing)
●
Reduction of the pressure at motor inlet
(PA) decreases the pressure in chamber
(S1). When it drops beyond the spool
switching pressure, the spool is returned to
the left by spring (20), reducing the pres-
sure at outlet passage (B1). At this time,
the motor continues rotating due to its iner-
tial force, thus pressure on the outlet port
(MB) is increased.
●
When the pressure rises above the set
pressure of the suction safety valve (8A),
the poppet opens. The pressurized oil
passes through notch (A1) of spool (19)
into chamber (MA) of the circuit at the op-
posite side.
ZX215-1002105
MB
B1
A1
20
S1
PB
PA
MA
MB
Travel control valve
ZX215-1002107
MA
MB
Spool
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