---
title: "Parts of pressurized and non-pressurized RoR intake"
subject: "Hydropower Engineering"
chapter: 5
key: "semester_7/hydropower_engineering:intake-parts-pressurized-nonpressurized-sketch"
source: https://www.bctengineer.com/q/semester_7/hydropower_engineering/intake-parts-pressurized-nonpressurized-sketch
site: BCT Engineering
---

# Parts of pressurized and non-pressurized RoR intake

Hydropower Engineering · Chapter 5: Headworks of Run-of- River (RoR) Plants

- Asked in: 2076 Chaitra, 2+6 marks
- Video: [RoR Headworks Intake Mastery #ror #water #diversion #weir](https://www.youtube.com/watch?v=7NTjkrUl8Bg) — Hydropower
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/hydropower_engineering/intake-parts-pressurized-nonpressurized-sketch
- Whole chapter: https://www.bctengineer.com/md/semester_7/hydropower_engineering/chapter-5

## Question

What are the main parts of non-pressurized and pressurized ROR intake? Present the general arrangement of such intakes in neat proportionate sketches.

## Short answer

Non-pressurized intake parts: approach channel, sill, trash rack, gate, transition, gravel trap and undersluice. Pressurized intake parts: trash rack, bell-mouthed entrance, minimum submergence with anti-vortex device, service and emergency gates, air vent, and transition to the pressure tunnel.

## Answer

#### Main parts of a non-pressurized RoR intake
1. **Approach channel / river training** with guide wall.
2. **Intake sill** (about 1.0-1.5 m above the undersluice or river bed) to stop bed load.
3. **Trash rack** (inclined at 70-80°) with a trash boom in front.
4. **Gate** (regulating gate) with a stop-log slot and hoist deck.
5. **Transition / bell-mouth** to the **gravel trap** and the **approach canal / settling basin**.
6. **Flushing (undersluice) gate** and flood wall.

```text
NON-PRESSURIZED INTAKE (section)
 pond ~~~~~~~~~~~~~~~~~~~~~~~
      boom  | hoist deck
   --o--    |  |gate
 trash  |##\ |  |
 rack   |##  \|  |_______ free flow --> canal
 sill   |_______|
 ///////////////////////////// river bed
```

#### Main parts of a pressurized intake
1. **Approach and trash rack** (inclined or vertical, large area, with rake).
2. **Bell-mouthed entrance** (to reduce entry loss).
3. **Minimum submergence** below the lowest operating level, with an anti-vortex device.
4. **Emergency gate and service gate** in a gate shaft, with an **air vent** behind the gate.
5. **Transition** from rectangular to the **circular pressure tunnel/penstock**.

```text
PRESSURIZED INTAKE (section)
 min WL ~~~~~~~~~~~~~~~~~~~~~~~~
        |  air vent
 rack   |##  |gate|
 S      |##  |    |
 _______|bell-|____> pressure tunnel (full)
        mouth
```
Proportions: rack velocity 0.8-1.0 m/s; the bell-mouth length is about 1.5-2 times the conduit height; the submergence is chosen by the vortex criterion $S\ge C\,V\sqrt D$.

## Check yourself

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

1. Which is a part of a non-pressurized intake?
   A. Air vent behind emergency gate
   B. Surge shaft
   C. Penstock bifurcation
   D. Sill, trash rack, regulating gate and gravel trap transition
   Answer: D. Air vent and gate shaft belong to pressurized intakes. (Key point: Non-pressurized parts)

2. Why is an air vent provided behind the gate of a pressurized intake?
   A. To admit air behind the gate and avoid negative pressure when closing
   B. To release sediment
   C. To cool the gate
   D. To raise submergence
   Answer: A. An air vent behind the gate prevents vacuum in the conduit. (Key point: Pressurized parts)

3. How is submergence in a pressurized intake chosen?
   A. By the trash rack spacing
   B. By the vortex criterion S >= C V sqrt(D)
   C. By the settling velocity
   D. By Manning's equation
   Answer: B. Adequate submergence prevents air-entraining vortices. (Key point: Submergence)

## Related in Hydropower Engineering

- [Pressurized vs non-pressurized intakes](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Aintake-pressurized-vs-nonpressurized) — Hydropower Engineering, chapter 5, asked 2×
- [RoR headworks arrangement and functional requirements](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Aror-headworks-arrangement-requirements) — Hydropower Engineering, chapter 5, asked 3×
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- [Common RoR intakes in Nepal; site selection](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Aror-common-intakes-nepal-location) — Hydropower Engineering, chapter 5, asked 2×
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