Draft tube

[1] This draft tube at the end of the turbine increases the pressure of the exiting fluid at the expense of its velocity.

This means that the turbine can reduce pressure to a higher extent without fear of back flow from the tail race.

[2] Using a draft tube also has the advantages of placing the turbine structure above the tail race so that any required inspections can be made more easily and reducing the amount of excavation required for construction.

V2 = Fluids velocity at inlet of draft tube or at the outlet of turbine V3 = Fluids velocity at outlet of draft tube g= gravitational acceleration hd = head losses in draft tube A draft tube allows a turbine to be placed above the tail race and simultaneously allows it to operate at the same efficiency as if it was placed at the tail race.

[3] The height of draft tube is an important parameter for avoiding cavitation.