How do tipper truck's work?

At the front of the dump bed, there is a collapsing sectional arm, in which each section collapses into the larger section below it when the bed is down. To raise the bed, the Power Take Off (PTO) is engaged to pump hydraulic oil into the cylinder which contains the sectional armature. The pressure from the hydraulic oil pushes up against these, forcing them up, which, in turn, raises the dump body.