Return to Master Table of Contents ARM OPERATING CIRCUIT The arm operating circuit includes both the right and left hydraulic main pumps, the both sides of the control valve, arm regen. valve, 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 (5,112 psi) have been installed at the crowd and dump cylinder ports on ARM1 side of the control valve to protect the circuit and system components from possible damage caused by shocks or overload pressure.
additional protection - to prevent cavitation of the cylinder - is provided by a make-up 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. 2 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 ARM1 and ARM2 of the control valve simultaneously. ARM CYLINDER When secondary pilot pressure reaches 7 - 10 kg/cm (100 - 142 psi), the arm control valve spool on the ARM1 and ARM2 spools open. Output flow from both pumps are directed to the arm cylinder.
2 When working in the arm crowd mode, under certain conditions, arm cylinder could be forced out by the weight of the arm and bucket itself. At this time insufficient oil flow to the cylinder could lead to cavitation in the cylinder head 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. PUMP(L) PUMP(R) ATS0770L Figure 4 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 ARM1 and ARM2 the control valve simultaneously.
ARM CYLINDER When pilot pressure reaches 7 - 10 kg/cm (100 - 142 psi), the control spools open allowing oil from PUMP(L) and PUMP(R) to flow to the arm cylinder. 2 PUMP(L) PUMP(R) ATS0780L Figure 5 Page 7 Hydraulic System Troubleshooting, Testing and Adjustment ARM2 ARM CROWD PILOT REGEN V/ ARM1 V ARM DUMP PILOT ARM2 ARM1