To take out petrol from tank of bike we use a rubber pipe. One end of pipe is dip inside the tank and petrol is sucked from other open end. Once the petrol starts coming then it steadily flows out provided that the level of open end of pipe is below the level of tank. This is called as action of syphon.

Similarly when the water comes out from the hydraulic turbine (Francis and Kaplan or other reaction turbine) then if we apply a pipe on the exit of turbine for developing action of syphon then it will start pulling water from turbine to develop extra hydraulic power ( together with push force of water when it enters the turbine). That pipe is called as draft tube. Learn the concept of Draft tube by this easy to understand lecture....

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