Draft Tube is a connecting pipe which is fitted generally at the outlet or exit of turbines which and convert kinetic energy of water at outlet of turbine to static pressure. It helps to avoid wastage of kinetic energy of water that flow from the outlet of turbines.
It is generally fitted in the power turbines like reaction turbines, Kaplan turbines or Francis turbines.
The diameter of draft tube is small near the inlet and large near its outlet.The outlet of draft tube is always submerged in water.

The draft tube increases the pressure of the exiting fluid in expense of its kinetic energy and velocity. It increases the efficiency of turbines.

It is located just under the runner and allow to decelerate the flow velocity exit from the runner.
Materials that are used to create draft tube are cast steel and cemented concrete.
Efficiency of a draft tube is the actual kinetic energy that is converted to static pressure.