Explanation:

The Pelton turbine is the water turbine that does not require a draft tube. Let's understand why.

Draft Tube:
A draft tube is a component used in water turbines to recover the energy of the water leaving the runner and convert it into useful work. It is a conical or cylindrical-shaped pipe that creates a low-pressure region at the outlet of the turbine, allowing the water to flow out smoothly. The draft tube helps in increasing the overall efficiency of the turbine by reducing the kinetic energy losses in the water leaving the turbine.

Pelton Turbine:
The Pelton turbine is a type of impulse turbine used for high head applications, where the water pressure is high. It consists of a wheel or rotor with multiple buckets or cups arranged around its periphery. The water jet from a nozzle strikes the buckets tangentially, imparting a high velocity to the water. The kinetic energy of the water jet is converted into mechanical energy as it strikes the buckets. The buckets are designed in such a way that the water jet is split into two halves, reversing its direction and leaving the cups with a low velocity.

Reason for not requiring a draft tube:
The Pelton turbine does not require a draft tube because of the way it operates. When the water jet leaves the buckets, it has a relatively low velocity. This low-velocity water can be discharged directly into the tailrace or tailrace channel without the need for a draft tube. The water leaving the turbine does not possess enough kinetic energy to cause significant losses or eddies. Therefore, a draft tube is not necessary for the Pelton turbine.

In contrast, other types of turbines like the propeller, Kaplan, and Francis turbines operate with a higher volume flow rate and lower pressure head. These turbines require a draft tube to recover the kinetic energy of the water leaving the runner and minimize losses.

Overall, the Pelton turbine is uniquely designed to operate without a draft tube, making it suitable for high head applications where the available water pressure is high.