Which of the following are correct regarding pelton turbine? (1). It is an impulse turbine. (2). Suitable for high head and low discharge. (3). It uses a draft tube. (4). Buckets are mounted on periphery of runner.
- A1, 2 and 4 onlyCorrect
- B1, 3 and 4 only
- C2 and 3 only
- DAll of the above
Solution
Concept
The Pelton wheel is an impulse turbine where the total energy of water is converted into kinetic energy by a nozzle before hitting the buckets mounted on the runner.
Formula
Specific Speed (Ns) = (N × √P) / H5/4
Step-by-step solution
1. Pelton turbines use the kinetic energy of a jet, making them impulse turbines (Correct). 2. They are specifically designed for high head and low flow rates (Correct). 3. Draft tubes are used to recover pressure head in reaction turbines; Pelton wheels discharge directly into the tailrace at atmospheric pressure (Incorrect). 4. The runner consists of a circular disc with hemispherical or ellipsoidal buckets fixed to its periphery (Correct). 5. Conclusion: Statements 1, 2, and 4 are correct.
Explanation
A Pelton turbine is a tangential flow impulse turbine designed for high heads (typically > 250m) and low discharge. It operates at atmospheric pressure, so it does not require a draft tube, which is a characteristic feature of reaction turbines like Francis or Kaplan.
Shortcut
Remember: Impulse = High Head + No Draft Tube. Reaction = Low/Medium Head + Draft Tube.
Common mistake
Students often confuse the draft tube requirement; remember that only turbines submerged or under pressure (reaction turbines) need a draft tube to prevent cavitation and recover head.
Correct answer: A) 1, 2 and 4 only