Hydraulic Machines MCQ with answer and solution

Concept

Function of the draft tube

Step-by-step solution

1. The draft tube is a gradually expanding tube from the runner exit to the tail race. 2. Its expansion converts the kinetic energy at the runner exit into pressure energy (regain of head). 3. It also allows the turbine to be set above the tail water level.

Explanation

The diverging draft tube reduces the exit velocity and recovers part of the kinetic energy as pressure energy. This creates a pressure below atmospheric at the runner exit, increasing the effective head across the runner.

Shortcut

Draft tube = diffuser: KE → pressure.

Common mistake

Choosing "prevent cavitation".