The forearm cylinder of the Kato excavator is controlled by the spool 4 of the control valve (valve block A) and the spool 5 of the control valve (valve block B). When the forearm spool is in neutral, the forearm cylinder does not supply oil. When the forearm joystick moves forward or backward, the forearm extends or retracts. The make-up valve and the overload relief valve are installed at the two oil ports of the arm I spool.
When operating the arm, the pressure oil of pump A1 enters the arm cylinder through the arm I valve in the control valve (valve block B).
The pressure oil of pump A2 merges with the pressure oil in the forearm I through the control valve (valve block B), and then flows to the forearm cylinder. The forearm Ⅱ is connected to the series oil circuit, but in the control valve. The side arm Ⅱ is connected in parallel with the oil circuit to make it easy to control when working simultaneously.
When the forearm is moved in all directions, the oil return from the top of the forearm cylinder is only returned to the tank through the forearm I valve. In the fine-tuning control mode, the pilot pressure acting on the control valve (valve block B) is blocked by the solenoid valve block. The pressure oil of the pump AI is supplied to the bottom end of the forearm cylinder for easy operation.
(1) Forearm recirculation circuit
The arm Ⅰ is equipped with a recirculation device, so that the oil returned from the top of the arm cylinder is recirculated to the bottom.
(2) Forearm balance valve
The top of the forearm cylinder is equipped with a balance valve, which reduces the extension of the forearm cylinder by limiting oil leakage under load conditions.
