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

# Flanged joint and reflux valve

Water Supply Engineering · Chapter 9: Valves and Fittings

- Asked in: 2069 Asar, 4 marks
- Video: [Types of Pipe Joints in Environmental Engineering 🔥🔥🔥🔥](https://www.youtube.com/watch?v=Ipmmtwz4uuA) — Civil Notebook
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/water_supply_engineering/flanged-joint-reflux-valve
- Whole chapter: https://www.bctengineer.com/md/semester_5/water_supply_engineering/chapter-9

## Question

Describe briefly the flanged joint and reflux valve with neat sketches.

## Short answer

A flanged joint joins pipes via bolted circular plates with a gasket, ensuring a watertight seal and easy dismantling. A reflux valve prevents reverse flow by a hinged flap that opens for forward flow and shuts automatically under back pressure.

## Answer

#### Flanged joint
A flanged joint connects two pipes (or a pipe and a valve, pump or fitting) using flanges, which are circular plates fixed to the pipe ends by casting, welding or screwing. A gasket of rubber, rubber-fabric or lead is placed between the flange faces, and the flanges are bolted together, tightening the nuts evenly in turn (diagonally opposite bolts one after another).

```text
             bolt + nut
          ___  |  ___
         |   |=+=|   |
  =======|   | | |   |=======
   pipe  | F |g| | F |  pipe
  =======|   | | |   |=======
         |___|=+=|___|
               |
            bolt + nut
     F = flange,  g = gasket
```
- Used for valves, pumps, meters and exposed pipes, and in pump houses and treatment plants.
- Strong, watertight and easy to dismantle; but costly, and being rigid it cannot take bending or misalignment.

#### 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. What is a flange?
   A. A circular plate fixed on the pipe end
   B. A thread
   C. A rubber ring
   D. A lead plug
   Answer: A. Flanges are plates cast, welded or screwed to pipe ends. (Key point: Flange)

2. What is placed between flange faces?
   A. Cement mortar
   B. A gasket of rubber, rubber-fabric or lead
   C. Nothing
   D. Yarn
   Answer: B. The gasket seals the joint when bolts are tightened. (Key point: Gasket)

3. What is a limitation of flanged joints?
   A. Cannot take bending or misalignment, and costly
   B. Not watertight
   C. Weak
   D. Hard to dismantle
   Answer: A. They are strong but rigid and costly, easy to dismantle. (Key point: Use and limit)

4. How does a reflux valve work?
   A. Spring screw
   B. Flap opens with forward flow and shuts on reverse
   C. Float seals
   D. Wheel turns gate
   Answer: B. One-way flow only. (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×
- [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
- [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; reflux valve](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Avalves-purpose-reflux) — Water Supply Engineering, chapter 9
- [Expansion joint and flanged joint](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Aexpansion-flanged-joint) — Water Supply Engineering, chapter 8, asked 2×

## Related in other subjects

- [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×