ну вот , например,When the left control lever is pulled back, the arm spools in the main control valve are moved to the
roll in position by the pilot oil pressure from the remote control valve.
The oil from the front and rear pump flows into the main control valve and then goes to the large
chamber of arm cylinder.
At the same time, the oil from small chamber of arm cylinder returns to the hydraulic oil tank through
the arm spool in the main control valve. When this happens, the arm rolls in.
The cavitation which will happen to the bottom of the arm cylinder is also prevented by the make-up
valve in the main control valve.