---
title: "Purpose of valves; cutoff valve"
subject: "Water Supply Engineering"
chapter: 9
key: "semester_5/water_supply_engineering:valves-purpose-cutoff"
source: https://www.bctengineer.com/q/semester_5/water_supply_engineering/valves-purpose-cutoff
site: BCT Engineering
---

# Purpose of valves; cutoff valve

Water Supply Engineering · Chapter 9: Valves and Fittings

- Asked in: 2075 Chaitra, 4 marks
- Video: [Types of Water Valves -  Plumbing Valve Types](https://www.youtube.com/watch?v=6dBhE6bPsoY) — Learning Engineering
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/water_supply_engineering/valves-purpose-cutoff
- Whole chapter: https://www.bctengineer.com/md/semester_5/water_supply_engineering/chapter-9

## Question

What are the purposes of valves in pipelines? Describe the working and function of the cutoff valve with a neat sketch.

## Short answer

Valves isolate, regulate flow, prevent backflow, release air, relieve pressure, and drain lines. A cutoff (gate) valve fully opens or closes the line using a wedge gate moved by a screw spindle; it is not for throttling, and gives low head loss when open.

## Answer

#### Purposes of valves in a pipeline
Valves are fitted in a pipeline to:
1. start, stop or isolate the flow (for repair, cleaning, extension of the line),
2. regulate the discharge and the pressure,
3. prevent back flow (reflux valve),
4. release trapped air (air valve) or relieve excess pressure (safety valve),
5. drain the line (washout or scour valve).

#### Cutoff valve (sluice valve)
A cutoff valve (sluice or gate valve) is used to stop or allow the flow completely; it is not used for throttling.

```text
      wheel / spindle
          |
       __ | __
      |  [|]  |   <- gate (wedge) moves up and down
  ====|  | |  |====
      |__|_|__|
         body
```
- **Construction:** a cast-iron body with a wedge-shaped gate (disc) moving across the flow by a screw spindle turned with a hand wheel.
- **Working:** when the wheel is turned, the gate rises (valve open: full bore, little head loss) or goes down across the pipe (valve closed: tight shut-off).
- **Uses:** at the beginning of branches, at intervals on the main lines (sectional valves), before and after pumps and meters.

## Check yourself

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

1. Which is NOT a purpose of valves in a pipeline?
   A. Isolate flow for repair
   B. Drain the line
   C. Increase pipe strength
   D. Regulate discharge
   Answer: C. Valves control, isolate, drain, release air and prevent back flow; they do not strengthen pipes. (Key point: Valve purposes)

2. A cutoff valve is used for what?
   A. Releasing air
   B. Preventing back flow
   C. Throttling flow
   D. Fully stopping or allowing flow, not throttling
   Answer: D. Sluice valves are fully open or fully closed. (Key point: Cutoff use)

3. How does the gate act?
   A. Wedge gate moves across flow via screw spindle and hand wheel
   B. Spring lifts
   C. Flap swings
   D. Float rises
   Answer: A. Turning the wheel raises or lowers the gate. (Key point: Cutoff working)

4. Where are sectional cutoff valves placed?
   A. Nowhere
   B. At branches and intervals on main lines
   C. Only at taps
   D. Only in tanks
   Answer: B. They are placed at branch starts, at intervals, and around pumps and meters. (Key point: Location)

## Related in Water Supply Engineering

- [Purpose of valves; reflux valve](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Avalves-purpose-reflux) — Water Supply Engineering, chapter 9
- [Air valve: function and working](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Aair-valve) — Water Supply Engineering, chapter 9, asked 3×
- [Cutoff valve and reflux valve](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Acutoff-reflux-valves) — Water Supply Engineering, chapter 9

## Related in other subjects

- [Valve timing diagram of four-stroke engine](https://www.bctengineer.com/question.md?key=semester_6%2Finternal_combustion_engines%3Avalve-timing-diagram-four-stroke) — Internal Combustion Engines, chapter 4