---
title: "Pressurized vs non-pressurized intakes"
subject: "Hydropower Engineering"
chapter: 5
key: "semester_7/hydropower_engineering:intake-pressurized-vs-nonpressurized"
source: https://www.bctengineer.com/q/semester_7/hydropower_engineering/intake-pressurized-vs-nonpressurized
site: BCT Engineering
---

# Pressurized vs non-pressurized intakes

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

- Asked in: 2074 Ashwin, 4 marks; 2071 Chaitra, 3 marks (asked 2 times)
- 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-pressurized-vs-nonpressurized
- Whole chapter: https://www.bctengineer.com/md/semester_7/hydropower_engineering/chapter-5

## Question

Differentiate between pressurized and non-pressurized intakes in a RoR system.

## Short answer

Non-pressurized intakes lead to free-surface canals/tunnels; pressurized intakes lead to pressure conduits and are fully submerged. Pressurized intakes require greater submergence, anti-vortex devices, and air vents; non-pressurized are simpler and cheaper. Pressurized intakes have a bell-mouth transition and service/emergency gates in a shaft.

## Answer

A **non-pressurized (free-surface) intake** leads water into a canal or a free-surface tunnel, so the flow has a free surface. A **pressurized intake** leads water into a pressure tunnel or penstock, so the opening is fully submerged below the minimum water level and the conduit runs full.

| Point | Non-pressurized intake | Pressurized intake |
|---|---|---|
| Flow in the conduit | Open channel flow with a free surface | Closed conduit under pressure |
| Typical use | RoR plants taking water to a settling basin and open canal or free-flow tunnel | Storage plants, or RoR with a pressure headrace tunnel |
| Intake opening | Orifice/side opening with sill; may be partially submerged | Always fully submerged below minimum operating level |
| Vortex and air entry | Not critical | Critical: needs enough submergence, anti-vortex devices and an air vent |
| Water level variation | Small (weir pond is nearly constant) | Large (reservoir drawdown) |
| Transition | Short, to the canal width | Long bell-mouth from rectangular to circular tunnel |
| Gate | Regulating gate or stop-log at the entrance | Service gate (and emergency gate) in a gate shaft |
| Trash rack | Moderate size, can be raked from the top | Large, inclined, with trash-rake machine |
| Sediment | Gravel trap and settling basin follow | Sediment excluded by a high sill |
| Cost | Cheaper, simple | More costly, since structure is deeper and heavier |

## Check yourself

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

1. What flow does a non-pressurized intake feed?
   A. Full pressure flow in a penstock
   B. Free-surface flow in a canal or open tunnel
   C. Flow only in a siphon
   D. Pumped flow
   Answer: B. Non-pressurized intakes lead to open-channel conduits. (Key point: Flow type)

2. Which intake needs enough submergence, anti-vortex devices and an air vent?
   A. Pressurized intake
   B. Non-pressurized intake
   C. Both equally
   D. Neither
   Answer: A. A pressurized opening must stay fully submerged below minimum level to avoid air entry. (Key point: Vortex concern)

3. Pressurized intakes are typical of which plants?
   A. RoR plants with open canal
   B. Micro-hydro with Tyrolean weirs
   C. Storage plants or RoR with a pressure headrace tunnel
   D. Only diversion canals
   Answer: C. They feed pressure tunnels or penstocks. (Key point: Typical use)

## Related in Hydropower Engineering

- [Parts of pressurized and non-pressurized RoR intake](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Aintake-parts-pressurized-nonpressurized-sketch) — Hydropower Engineering, chapter 5
- [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×

## Related in other subjects

- [Unique vs non-unique address decoding](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Aunique-vs-nonunique-decoding) — Instrumentation II, chapter 2