SYSTEM / Control System Counterweight Removal and Installation Control (Optional) Purpose: Applies back-pressure to the main relief valve, increases main relief pressure and the hoist / lower power improves. Or, Controls pump delivery flow rate and makes fine op- eration easy. Operation: 1. When the counterweight hoist / lower lever (op- tional) is operated, the pressure sensor (coun- terweight) detects pilot pressure and sends the signal to MC. 2. MC activates solenoid valve unit (SG). 3. Pressure oil from the pilot pump flows to the back of main relief valve. 4. Pressure oil compresses the spring of main relief valve and relief pressure increases.
(Refer to the Control Valve group / COMPONENT OPERA- TION.) 5. MC compares actual pump displacement angle detected by the pump 1 or 2 regulator pressure sensor with the target pump displacement angle. MC calculates required oil amount and activates the pump control solenoid valve. 6. Delivery flow rates of pumps 1, 2 become mini- mum. NOTE: Main Relief Pressure: During normal operation: 31.9 MPa (325 kgf/cm 2 , 4638 psi) During pressure increasing operation: 34.3 MPa (350 kgf/cm 2 , 4987 psi) T2-2-36