---
title: "Classification of water turbines"
subject: "Energy Environment and Society"
chapter: 3
key: "semester_7/energy_environment_and_society:water-turbines-impulse-reaction"
source: https://www.bctengineer.com/q/semester_7/energy_environment_and_society/water-turbines-impulse-reaction
site: BCT Engineering
---

# Classification of water turbines

Energy Environment and Society · Chapter 3: Renewable Energy Sources

- Asked in: 2074 Asoj, 1+3 marks; 2071 Shrawan, 1+2 marks; year not given (asked 2 times)
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/energy_environment_and_society/water-turbines-impulse-reaction
- Whole chapter: https://www.bctengineer.com/md/semester_7/energy_environment_and_society/chapter-3

## Question

How do you classify the water turbines? Differentiate between impulse and reaction turbines.

## Short answer

Water turbines are classified by action, head, flow direction, specific speed, and shaft position. In impulse turbines all pressure energy becomes kinetic energy in the nozzle and the runner operates at atmospheric pressure without a draft tube. In reaction turbines pressure drops through the runner, the casing is full of water, and a draft tube is needed.

## Answer

A **water turbine** converts the kinetic and pressure energy of water into mechanical rotation of a shaft that drives a generator.

#### Classification of water turbines
1. **By action of water:**
   - Impulse turbines (Pelton, Turgo, Cross-flow/Banki)
   - Reaction turbines (Francis, Kaplan, Propeller)
2. **By head:** high head (above 250 m, Pelton), medium head (60–250 m, Francis), low head (below 60 m, Kaplan/propeller).
3. **By flow direction:** tangential flow (Pelton), radial flow (Francis, older), mixed flow (modern Francis), axial flow (Kaplan, propeller).
4. **By specific speed:** low (Pelton), medium (Francis), high (Kaplan).
5. **By shaft position:** horizontal or vertical.

#### Impulse vs reaction turbine
| Point | Impulse turbine | Reaction turbine |
|---|---|---|
| Energy conversion | All pressure energy is converted to kinetic energy in the nozzle before the runner | Only part is converted before the runner; the rest changes as water flows through the runner |
| Pressure | Atmospheric pressure at the runner | Pressure above atmospheric at inlet, and below at outlet |
| Casing | Not full of water; casing just protects | Runner is completely enclosed and full of water |
| Head | High head, low flow | Low to medium head, high flow |
| Draft tube | Not needed | Needed |
| Flow regulation | Nozzle and spear valve | Guide vanes (wicket gates) |
| Examples | Pelton, Turgo, Cross-flow | Francis, Kaplan |
| Cavitation | Not a problem | A risk |
| Specific speed | Low | Medium to high |

In Nepal, Pelton and cross-flow turbines are used in micro/small hydro in the hills, while Francis is used in medium-head plants such as Kaligandaki A, and Pelton in high-head plants such as Khimti and Upper Tamakoshi.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Which turbines are impulse turbines?
   A. Francis and Kaplan
   B. Pelton, Turgo and Cross-flow
   C. Pelton and Kaplan
   D. Francis and Turgo
   Answer: B. Pelton, Turgo and cross-flow are impulse; Francis, Kaplan and propeller are reaction. (Key point: Classification by action)

2. What is the pressure condition at the runner of an impulse turbine?
   A. Atmospheric pressure
   B. Above atmospheric at inlet and below at outlet
   C. Always below atmospheric
   D. Very high pressure throughout
   Answer: A. Impulse runners operate at atmospheric pressure; reaction runners have pressure change across them. (Key point: Pressure at runner)

3. Which statement is correct?
   A. Impulse turbines need a draft tube
   B. Reaction turbines have no cavitation risk
   C. Neither turbine needs a draft tube
   D. Reaction turbines need a draft tube and have cavitation risk
   Answer: D. The runner of a reaction turbine is full of water and discharges below atmospheric pressure, so a draft tube is needed and cavitation is a risk. (Key point: Draft tube and cavitation)

4. Which turbine suits high head (above 250 m)?
   A. Kaplan
   B. Francis
   C. Pelton
   D. Propeller
   Answer: C. Pelton suits high head and low flow; Francis medium head; Kaplan low head. (Key point: Head selection)

## Related in Energy Environment and Society

- [Characteristics of impulse and reaction turbines](https://www.bctengineer.com/question.md?key=semester_7%2Fenergy_environment_and_society%3Aimpulse-reaction-characteristics) — Energy Environment and Society, chapter 3

## Related in other subjects

- [Impulse and reaction steam turbines compared](https://www.bctengineer.com/question.md?key=semester_5%2Ffluid_machines%3Aimpulse-reaction-steam-turbine-types) — Fluid Machines, chapter 5
- [Impulse versus reaction turbines](https://www.bctengineer.com/question.md?key=semester_6%2Fhydro_power%3Aimpulse-vs-reaction-turbines) — Hydro Power, chapter 7, asked 2×
- [Impulse versus reaction turbines](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Aimpulse-vs-reaction) — Power Plant Equipment, chapter 7, asked 2×
- [Impulse and reaction turbines compared](https://www.bctengineer.com/question.md?key=semester_5%2Ffluid_machines%3Aimpulse-vs-reaction-turbine) — Fluid Machines, chapter 3