Arm Operating Circuit; Arm Crowd Circuit; Arm Dump Circuit - Doosan DX140R Shop Manual

Arm Operating Circuit

The arm operating circuit includes both the front and rear
hydraulic main pumps, the right and left halves of the control
valve, a slow return orifice, and the arm cylinder. The circuit can
be operated in the two-stage speed control mode which works
through both halves of the control valve and doubles the volume
of oil flowing to the cylinder.
Overload relief valves set at 360 kg/cm
installed at the AM 1 and AMD 1 ports on the right side of the
control valve to protect the circuit and system components from
possible damage caused by shocks and/or overload pressure.
Additional protection - to prevent cavitation of the cylinder - is
provided by a makeup valve and reservoir return circuit, which
ensures that the volume of oil going to the cylinder will not
exceed the volume of oil coming out.

Arm Crowd Circuit

When the arm control lever is put in the crowd mode, the left
side pilot valve generates secondary pressure that is transmitted
to the AM1 and AM2 spools of the control valve simultaneously.
When secondary pilot pressure reaches 7 - 9 kg/cm
psi), the arm control valve spools AM1 and AM2 open. Output
flow from both halves of the pump assembly is directed to the
arm cylinder.
When working in the arm crowd mode, under certain conditions,
oil in the arm cylinder could suddenly be forced out by the weight
of the arm and bucket. Insufficient oil flow to the cylinder could
lead to cavitation in the cylinder and/or surging or irregular
movement. This is prevented by a regeneration valve attached
to the control valve which maintains the balance between oil
flowing into the cylinder and oil flowing out.

Arm Dump Circuit

When the arm control lever is put in "dump" mode, the left side
pilot valve generates secondary pilot pressure that goes to both
spools AM1 and AM2 of the control valve simultaneously.
When pilot pressure reaches 7 - 9 kg/cm
control spools open, allowing oil from PUMP (F) and PUMP (R)
to flow to the arm cylinder.
Hydraulic System Troubleshooting, Testing and Adjustment
Page 10
2
(5,112 psi) have been
2
(100 - 130
2
(100 - 130 psi), the
ARM
CYLINDER
REGENERATION VALVE
AM2 PILOT VALVE
PL TL
CONTROL
VALVE(L)
PUMP(F)
Figure 4
AM2 AMD2 PILOT VALVE
PL
TL
CONTROL
VALVE(L)
PUMP(F)
Figure 5
AMD1 AM1
PR
CONTROL
VALVE(R)
PUMP(R)
FG015149
ARM
CYLINDER
AMD1 AM1
PR
CONTROL
VALVE(R)
PUMP(R)
FG015150
SP001942