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Pressurized vs non-pressurized intakes
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.
Differentiate between pressurized and non-pressurized intakes in a RoR system.
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 |
✓ Answer checked by Claude Opus 5.5 (high effort)
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