The crane begins by lifting the opening grab, during which the piston rod of the hydraulic cylinder extends. The remote control grab is then positioned over the bulk materials by the crane. Once in place, the steel wire rope is slackened, allowing the piston rod of the cylinder to descend along with the transverse frame under its own weight.
As the piston moves downward, the hydraulic oil in the lower chamber is displaced and flows into the upper chamber through a one-way valve mounted on the piston. Any excess oil is forced back into the tank.
When the piston reaches the bottom of the cylinder, the oil in the lower chamber returns to the tank via the hose pipes. In contrast, the oil in the upper chamber remains connected through hoses to the solenoid valve and the cartridge valve.
At this stage, the solenoid valve remains in the locked position, preventing oil flow. As the crane begins to lift the steel wire rope, the transverse frame rises along with the through beam. The lifting force is transmitted through the rope to the remote control grab head and piston.
Since the upper chamber of the cylinder is locked, the hydraulic oil trapped inside cannot escape, resulting in a buildup of pressure. This pressure causes the cylinder and the through beam to rise together, allowing the scoops to close. The grab, now loaded with material, is lifted along with the rope.
Once the remote control grab has been raised and moved to the designated location by the crane, the operator presses a button on the remote control. This action causes the transverse frame-together with the piston rod-to rise relative to the grab head, while the through beam descends due to its own weight. The pressure in the upper chamber is released, allowing the grab to open and discharge the materials.
