Pantographs are single point power contact for the locomotives or power car. They collect current from overhead lines. So, they must maintain good contact under all running conditions. Pantographs maintain contact either by spring or air pressure. Compressed air pressure is preferred for high-speed operation. The pantograph is connected to a piston in a cylinder and air pressure in the cylinder maintains the pantograph in the raised condition.
Earlier pantographs are diamond-shaped "pantograph" with the contact head at the top. Two contact faces are generally provided. The modern systems use single arm pantographs just half of the original shape provided with a neater looking design.
the most sophisticated pantographs have special horns and come with a small air pressure tube which, in time pressure is lost, will cause the pan to lower automatically and so reduce the possible wire damage.
