As shown in Figure 3-3, the two cylinders of the arm of the Kato excavator are controlled by the spool 4 of the control valve (valve block B) and the spool 3 of the control valve (valve block A). When the spool of the boom is in neutral, the boom cylinder stops. When the boom control lever moves forward or backward, the cylinder extends or retracts to raise or lower the boom.
The oil ports at both ends of the main arm Ⅰ spool are equipped with a supplementary valve for preventing cavitation and an overload relief valve, so that when the spool is in neutral, no abnormal pressure will be generated in the hydraulic circuit due to external force. When the boom spool moves to the extended end, the pressure oil of pump Pl and pump P2 merges and flows into the bottom end of the boom cylinder.
If the boom spool is transferred to the retracted end, the boom Ⅱ spool is in neutral, and only the pressure oil of the pump P passes through the top of the boom cylinder
(1) Boom recirculation circuit
The retracted end of the boom spool is equipped with a recirculation device to recirculate the oil at the bottom of the cylinder to the bottom.
(2) Boom lifting priority circuit
① When the boom is lifted or the bucket is loaded, the pressure oil of the pump P1 is supplied to the bottom end of the boom cylinder through the parallel channel in the control valve (valve block A). The pressure oil of the pump P2 is supplied to the boom and bucket of the control valve (valve block B). However, the pilot pressure of 52 kgf/cm2 is used to adjust the stroke of the bucket spool. Therefore, the spool stroke will be incomplete and the oil passage will be shortened. Therefore, ensure that the working pressure of the boom is raised. ②Turntable work (HD820IC) pump P2 pressure oil The parallel passage in the control valve (valve block B) is supplied to the bottom end of the boom cylinder. The pressure oil of the pump P1 passes through the parallel passage in the control valve (valve block A) to the boom and the turntable, but the pilot pressure of the boom II also acts on the boom lift priority valve to shorten the oil passage of the turntable, so it is supplied to the boom Youyou
(3) Boom lock valve
The lock valve is installed at the bottom of the boom cylinder to limit the natural sinking of the boom, thereby reducing oil leakage in the cylinder
(4) Slow Arm Mode
When the slow mode of the boom is selected, the decreasing pilot pressure of 52kgcm2 is used to limit the spool travel through the solenoid valve block to ensure the fine-tuning control range when the pressure drops.
