Komatsu PC500LC-10R Shop Manual page 278

COMPONENT PARTS OF HYDRAULIC SYSTEM
If abnormally high pressure occurs in the boom cylinder bottom circuit, the pressurized oil in port (B) pushes
open check valve (6), and suction safety valve (3) operates.
When arm hydraulic drift prevention valve (if equipped) is installed to the arm cylinder head circuit, the higher
one of the boom cylinder bottom circuit pressure and the arm cylinder head circuit pressure pushes open check
valve (6) or (6A), and suction safety valve (3) operates.
ARM QUICK RETURN VALVE OF CONTROL VALVE
FUNCTION OF ARM QUICK RETURN VALVE OF CONTROL VALVE
When the arm is moved OUT, much oil returns from the cylinder bottom. This function is used to decrease the
pressure loss in this process.
OPERATION OF ARM QUICK RETURN VALVE OF CONTROL VALVE
When the arm "OUT" operation is performed
1.
When the arm "OUT" operation is performed, the pilot pressure from the PPC valve pushes the pilot piston
(1).
2.
The pressurized oil in the chamber (b) inside the valve is drained through the orifice (c).
3.
The pressurized oil in the arm cylinder bottom flows to drain port (T) through orifice (a), chamber (b), and
orifice (c).
4.
Chamber (b) is connected to drain port (T), and the pressure in chamber (b) decreases.
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10 STRUCTURE AND FUNCTION
PC500LC-10R
AEP21611