Pressure operated grab for stones

摘要

The grab uses pressure operated drives (7,15) for aligning stones lengthwise, and for gripping and extracting them. The drives operate in a chronological sequence one after each other. At least two of the drives are connected to a common pressurised circuit (18,19). The pressurised side of the first drive is connected to a valve (21) which operates at a predetermined pressure, and which switches the pressurised supply to a subsequent drive. The valve may also have an operating pressure of between 10 and 50 percent of the full system pressure.