---
title: "Spillway gates and radial gate"
subject: "Hydro Power"
chapter: 6
key: "semester_6/hydro_power:spillway-gates-radial-gate"
source: https://www.bctengineer.com/q/semester_6/hydro_power/spillway-gates-radial-gate
site: BCT Engineering
---

# Spillway gates and radial gate

Hydro Power · Chapter 6: Spillways

- Asked in: 2082 Kartik, 1+3 marks
- Video: [How Different Spillway Gates Work](https://www.youtube.com/watch?v=Ry_3icwd68o) — Practical Engineering
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/hydro_power/spillway-gates-radial-gate
- Whole chapter: https://www.bctengineer.com/md/semester_6/hydro_power/chapter-6

## Question

List the various types of spillway gates and describe the radial gate with a neat sketch.

## Short answer

Types include vertical lift, radial, drum, sector, rolling, flap gates and flash boards. A radial gate has a curved skin plate fixed to radial arms that pivot on trunnion pins. The resultant water pressure passes through the trunnion, requiring only a small hoisting force.

## Answer

#### Types of spillway gates
1. Vertical lift gates – plain sliding, fixed-wheel (roller) and Stoney gates
2. Radial (Tainter) gates
3. Drum gates
4. Sector gates
5. Rolling (roller) gates
6. Flap gates
7. Flash boards and stop logs

#### Radial (Tainter) gate
A **radial gate** has a curved steel **skin plate**, which is a part of a cylinder, supported by **radial arms** that converge to **trunnion pins** fixed on the piers. The gate rotates about the trunnion to open or close.

```text
              hoist rope
               |
     ~~~~~~~~~ |\   skin plate (curved)
   reservoir   | \
   ~~~~~~~~~~~ |  \ ---- arm ----o trunnion
               |  /               (on pier)
               | /  ---- arm ---/
   ____________|/__________________
         crest   sill    flow -->
```

**Working and features:**
- The skin plate is curved concentric with the trunnion, so the **resultant water pressure passes through the trunnion pin**. Water pressure therefore produces no moment about the pin, and the hoist only lifts the gate's own weight and overcomes pin and seal friction.
- The gate is raised by rope or chain hoists or hydraulic cylinders; water flows under the gate.
- Rubber seals at the sides and bottom make it watertight; no deep slots in piers are needed, so flow is smooth.

**Advantages:** small hoisting force, simple and reliable, good for large openings (up to about 20 m × 20 m), easy automatic control, cheaper than vertical gates of the same size.

**Disadvantages:** piers must be long to hold the trunnions; trunnion anchorage carries large concentrated loads; requires accurate fabrication.

## Check yourself

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

1. A radial gate has
   A. a curved skin plate supported by radial arms on trunnion pins in the piers
   B. a flat plate on rollers
   C. a hollow drum hinged upstream
   D. a horizontal cylinder rolled up racks
   Answer: A. The skin is part of a cylinder. (Key point: Construction)

2. The hoist of a radial gate only has to
   A. resist the full water pressure
   B. lift the gate weight and overcome pin and seal friction
   C. support the pier
   D. pump water into a chamber
   Answer: B. Resultant water force passes through the trunnion. (Key point: Hoist force)

3. A disadvantage of radial gates is
   A. very high hoisting force
   B. deep slots in piers
   C. long piers and large concentrated trunnion loads
   D. poor reliability
   Answer: C. Piers must hold the trunnions. (Key point: Disadvantage)

4. Radial gates avoid deep slots in piers, which gives
   A. higher friction
   B. lower span capability
   C. need for stop logs
   D. smooth flow
   Answer: D. No deep slots means smooth flow and low cost. (Key point: Advantage)

## Related in Hydro Power

- [Spillway function, vertical and radial gates](https://www.bctengineer.com/question.md?key=semester_6%2Fhydro_power%3Aspillway-function-vertical-radial-gate) — Hydro Power, chapter 6
- [Types of spillway gates](https://www.bctengineer.com/question.md?key=semester_6%2Fhydro_power%3Aspillway-gate-types) — Hydro Power, chapter 6, asked 2×

## Related in other subjects

- [Types of spillway crest gates](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Aspillway-crest-gate-types) — Hydropower Engineering, chapter 4, asked 2×
- [Purposes of spillway; types of gates](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Aspillway-purposes-and-gate-types) — Hydropower Engineering, chapter 4
- [XOR gate using minimum NAND gates](https://www.bctengineer.com/question.md?key=semester_3%2Fdigital_logic%3Axor-using-nand-only) — Digital Logic, chapter 2, asked 2×
- [X-OR gate using NAND gates only](https://www.bctengineer.com/question.md?key=semester_2%2Fbasic_electronics_engineering%3Axor-using-nand) — Basic Electronics Engineering, chapter 6