The two cylinders of the boom 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 lever moves forward or backward, the cylinder extends or retracts to raise or lower the boom.
The oil ports at both ends of the boom I spool are equipped with supplementary valves and overload relief valves to prevent cavitation, so that when the spool is in neutral, no abnormal pressure will be generated in the hydraulic circuit due to external forces. When the boom valve core moves to the extension end, the pressure oil of the pump Pl and the pump P2 merge and flow 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 pump P passes through the top of the boom cylinder
(1) Boom recirculation circuit
The retracted end of the Boom I spool is equipped with a recirculation device to recirculate the oil at the bottom end of the cylinder to the bottom end.
(2) Boom lifting priority circuit
① During boom lifting or bucket loading, the pressure oil of pump P1 is supplied to the bottom end of the boom cylinder through the parallel passage in the control valve (valve block A). The pressure oil of the pump P2 is supplied to the boom and the 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, so the spool stroke will be incomplete and the oil passage will be shortened. Therefore, it is necessary to ensure that the working pressure of the boom is raised ②The pressure oil of the turntable work (HD820IC) pump P2 It is supplied to the bottom end of the boom cylinder through the parallel passage in the control valve (valve block B). 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 acts on the boom lift priority valve at the same time 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 restrict the boom from sinking naturally, thereby reducing oil leakage in the cylinder
(4) Boom slow mode
When the boom slow mode is selected, the 52kgcm2 of pilot pressure that drops is limited by the solenoid valve block to limit the spool stroke to ensure the fine-tuning control range when the pressure drops.
