Telescopic Applications: telescopic cylinders are generally divided into the built-in and external telescopic cylinder telescopic boom, boom-Cylinder reference lorry principle, external fuel tanks designed in accordance with the principle of pulleys, mainly used in sinking and deep foundation excavation. Built-in telescopic cylinders excavation depth 12 m below 13-30 meters optional external fuel tank, front bucket shells. Telescopic basic principles: a) Built-cylinder telescopic boom with wear-resistant, high-temperature tetragonal steel (Q690 or higher performance), through high-precision machining, first, Section III completely close fitting, through travel cylinder push or recycling the job done, this form of limited telescopic working depth, vertical excavation, but a very small turning radius, plus the long arm more complete than the two-stage complex working conditions. b) External cylinder telescopic tube is formed by dry-strength steel Quartet, made up of three sections or even multi-section type, use rope pulley principle of freedom with stretching, reaching maximum digging depth construction requirements, construction on city streets as the subway excavation, pit mining viaducts widespread use.