⭐ Upgrade to Pro - £19
Unlock all lessons and mock exams to pass Level 2 + Level 3 theory exams.
Upgrade nowSiphonic Action
Read through the material below, then test your understanding.
Module Lessons
Scientific Principles
SI Units and Measurement
Properties of Solid Materials (Metals)
Properties of Solid Materials (Plastics & Ceramics)
Mechanical Properties
Corrosion of Metals
Other Forms of Corrosion
Degradation of Plastics
Properties of Liquids (Water)
Properties of Liquids (Others)
Properties of Gases
Temperature and Heat
States of Matter
Sensible and Latent Heat
Conduction and Convection
Radiation and Expansion
Energy, Heat, and Power Calculations
Velocity, Acceleration, and Flow Rate
Force and Pressure
Siphonic Action
Mechanical Principles
Forces in Action
Lesson Overview
Siphonic action uses atmospheric pressure, liquid cohesion, and gravity to transfer fluids across an elevation break. In plumbing, this principle powers flushing mechanisms in WCs and urinals, but can also cause hazardous trap seal depletion if pipework is unventilated.
Learning Objectives
Explain the fundamental scientific principles governing siphonic action and fluid movement.
Identify the practical operation of useful siphonic devices including WC siphons and automatic flushing cisterns.
Recognise the causes, consequences, and prevention methods for unwanted siphonic action in domestic pipework.
Unlock the full lesson & knowledge check
Get lifetime access to every Level 2 & 3 lesson, 3500+ total questions, and timed City & Guilds mock exams.
Get Pro Access (£19)Already have Pro? Sign in
Interactive City & Guilds Level 2 and Level 3 plumbing lessons, flashcards and mock exams, built for UK students and professionals.
© 2026 PlumbingIQ. All rights reserved.