---
title: "Cutoff valve and reflux valve"
subject: "Water Supply Engineering"
chapter: 9
key: "semester_5/water_supply_engineering:cutoff-reflux-valves"
source: https://www.bctengineer.com/q/semester_5/water_supply_engineering/cutoff-reflux-valves
site: BCT Engineering
---

# Cutoff valve and reflux valve

Water Supply Engineering · Chapter 9: Valves and Fittings

- Asked in: 2079 Baisakh, 3 marks
- Video: [Environment lecture ! types of  Valve in pipe ! Sluice valve ! Reflux valve ! Air relief valve !](https://www.youtube.com/watch?v=Vei7FUX9Ze8) — NARAYANA COACHING CLASSES
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/water_supply_engineering/cutoff-reflux-valves
- Whole chapter: https://www.bctengineer.com/md/semester_5/water_supply_engineering/chapter-9

## Question

Describe the cutoff valve and the reflux valve with necessary sketches.

## Short answer

A cutoff (gate) valve uses a wedge gate moved by a screw spindle to fully open or close the flow with low head loss when open. A reflux (check) valve has a hinged flap that opens with forward flow and closes automatically on reverse flow to prevent backflow.

## Answer

#### Cutoff valve
A cutoff valve (sluice or gate valve) is used to fully stop or fully allow the flow; 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) that is moved across the flow by a screw spindle turned with a hand wheel.
- **Working:** when the wheel is turned, the gate either rises (valve open: full bore, little head loss) or comes down across the pipe (valve closed: tight shut-off).
- **Uses:** at the start of branches, at intervals along the main lines (sectional valves), and before and after pumps and meters.

#### Reflux valve
A reflux valve (also called a non-return or check valve) allows water to flow in one direction only and closes automatically when the flow tries to reverse.

```text
   flow ->   _______hinge
   =========|\       |=========
            | \ flap |   (flap lifts for
   =========|__\_____|=========  forward flow,
        valve seat           falls shut on reversal)
```
- **Construction:** a cast-iron body with a flap (door or disc) hinged at the top, which rests on a seat. Forward flow pushes the flap open; when the flow stops or reverses, the weight of the flap and the back pressure press it onto the seat.
- **Uses:** on the delivery side of a pump, to prevent back flow when the pump stops and to protect the pump from water hammer; on pipes from a reservoir that must not drain back; at the foot of a suction pipe (foot valve); and on rising mains and service connections to prevent back siphonage.

## Check yourself

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

1. Why is a cutoff valve not used for throttling?
   A. It is plastic
   B. It has a flap
   C. It is too small
   D. It is meant to be fully open or shut
   Answer: D. Throttling vibrates the gate and erodes the seat. (Key point: Cutoff use)

2. Why is head loss small when the cutoff valve is open?
   A. Full bore, gate clear of the flow
   B. It is partly open
   C. It has a flap
   D. It has bends
   Answer: A. The gate is lifted out of the waterway. (Key point: Open state)

3. What does a reflux valve prevent?
   A. Reverse flow
   B. Air entry
   C. Forward flow
   D. Leaks at taps
   Answer: A. It permits only one-direction flow. (Key point: Reflux)

## Related in Water Supply Engineering

- [Reflux valve and air relief valve](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Areflux-air-relief-valves) — Water Supply Engineering, chapter 9, asked 2×
- [Flanged joint and reflux valve](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Aflanged-joint-reflux-valve) — Water Supply Engineering, chapter 9
- [Reflux valve with sketch](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Areflux-valve) — Water Supply Engineering, chapter 9
- [Purpose of valves; cutoff valve](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Avalves-purpose-cutoff) — Water Supply Engineering, chapter 9
- [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

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- [Pressure variation after sudden valve closure](https://www.bctengineer.com/question.md?key=semester_4%2Fhydraulics%3Awater-hammer-pressure-time-valve-and-midpoint) — Hydraulics, chapter 4
- [Why joints are necessary; expansion joint](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Ajoints-why-expansion) — Building Technology, chapter 10, asked 2×