---
title: "Cross-flow (Banki-Mitchell) turbine"
subject: "Fluid Machines"
chapter: 3
key: "semester_5/fluid_machines:cross-flow-turbine-notes"
source: https://www.bctengineer.com/q/semester_5/fluid_machines/cross-flow-turbine-notes
site: BCT Engineering
---

# Cross-flow (Banki-Mitchell) turbine

Fluid Machines · Chapter 3: Water Turbine

- Asked in: year not given, 4 marks
- Video: [Cross Flow Turbine ENZY](https://www.youtube.com/watch?v=Hkq-LdzImfw) — dejenie dessie
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/fluid_machines/cross-flow-turbine-notes
- Whole chapter: https://www.bctengineer.com/md/semester_5/fluid_machines/chapter-3

## Question

Write short notes on the cross-flow (Banki-Michell) turbine, mentioning its construction, working and applications.

## Short answer

The cross-flow (Banki-Michell) turbine is a partial-admission impulse-reaction turbine with a cylindrical runner of curved blades. Water enters through a rectangular nozzle, passes through the runner twice (inward then outward), extracting energy. It is simple, cheap, self-cleaning, with flat efficiency around 80%, suitable for micro/mini hydro up to a few MW and heads 2–100 m.

## Answer

The **cross-flow turbine** (Banki-Michell or Ossberger turbine) is a partial-admission **impulse-reaction turbine** with a drum-shaped runner, used in small hydro plants.

```text
        water in
          |  nozzle with
          v  guide vane
        +-----+
       /   ___ \
      |  /     \ |   <- 1st pass: outside to inside
      | |  ( )  ||
      |  \_____/ |   <- 2nd pass: inside to outside
       \_________/
           |
        tailrace
```

#### Construction

- A cylindrical runner made of two end discs joined by 20 to 30 curved blades (flat strips bent to arc form, about 30 mm to 50 mm apart on rim).
- A rectangular nozzle of the width of the runner, with an adjustable guide vane (flow regulator), directs water at about 16 degrees to the tangent.
- The casing leads water to the tailrace. Head range is about 2 to 100 m.

#### Working

Water from the nozzle strikes the blades near the rim and flows **inward** through the runner (first pass, about 70 to 80 % of the power), crosses the empty space inside the drum and passes through the blades **outward** a second time (about 20 to 30 %). It thus crosses the runner twice, hence the name. The pressure at entry and exit is nearly atmospheric.

#### Advantages and applications

- Simple, cheap, easy to build locally and repair; suitable for micro and mini hydro (up to a few MW).
- Flat efficiency curve (about 80 % over a wide load range), by splitting the runner into sections of different width (1/3 and 2/3 as in Ossberger design).
- Self-cleaning, since the leaves and sand fall off in the second pass.
- Used for low to medium heads and widely used in rural electrification schemes.
- Disadvantage: peak efficiency (about 80 to 87 %) is lower than Pelton or Francis turbines.

## Check yourself

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

1. Why is the cross-flow turbine so named?
   A. Water crosses the runner twice, inward then outward
   B. Water flows across the shaft axis only once
   C. Two jets cross each other
   D. Water crosses from tailrace to nozzle
   Answer: A. Water passes through the blades inward (first pass) and again outward (second pass). (Key point: Two-pass working)

2. Roughly how much of the power is developed in the first pass?
   A. About 20 to 30 %
   B. About 50 %
   C. About 70 to 80 %
   D. About 100 %
   Answer: C. The first pass gives about 70 to 80 % and the second pass the remaining 20 to 30 %. (Key point: Power split)

3. Which feature gives the cross-flow turbine a flat efficiency curve over a wide load range?
   A. A draft tube
   B. Splitting the runner into sections of different width (1/3 and 2/3)
   C. A spear valve
   D. Using Kaplan blades
   Answer: B. Ossberger design uses unequal runner sections that are used according to load, keeping efficiency about 80 %. (Key point: Flat efficiency and self-cleaning)

## Related in Fluid Machines

- [Francis turbine: construction and working](https://www.bctengineer.com/question.md?key=semester_5%2Ffluid_machines%3Afrancis-turbine-working-components) — Fluid Machines, chapter 3
- [Kaplan turbine construction and working](https://www.bctengineer.com/question.md?key=semester_5%2Ffluid_machines%3Akaplan-turbine-working) — Fluid Machines, chapter 3
- [Derivation of Euler's turbine equation](https://www.bctengineer.com/question.md?key=semester_5%2Ffluid_machines%3Aeuler-turbine-equation-derivation) — Fluid Machines, chapter 1
- [Francis turbine velocity triangles and power](https://www.bctengineer.com/question.md?key=semester_5%2Ffluid_machines%3Afrancis-turbine-numerical) — Fluid Machines, chapter 3
- [Kaplan turbine discharge and blade angles](https://www.bctengineer.com/question.md?key=semester_5%2Ffluid_machines%3Akaplan-turbine-numerical) — Fluid Machines, chapter 3
- [Single-stage impulse turbine blade work and efficiency](https://www.bctengineer.com/question.md?key=semester_5%2Ffluid_machines%3Ade-laval-turbine-velocity-diagram-numerical) — Fluid Machines, chapter 5

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