Scientific Principles revision notes
The science behind the trade — pressure and head, heat and expansion, flow and units.
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C&G Unit 203: Hydraulics & Head Pressure
Head, pressure and thermal expansion
The head/pressure rule of thumb and why heated water needs expansion provision.
Heat transfer in plumbing systems: conduction, convection, and radiation
How heat energy moves through metals, liquids, and room spaces in domestic heating.
Plumbing science terms glossary
Short definitions of the physical-science terms that underpin plumbing and heating calculations.
States of matter and density: a science glossary
Mass, force, density and relative density, including the reference used for fuel gases.
Calculations: head & pressure
Converting between bar, metres head and kilopascals (worked example)
Switching a pressure between bar, metres of water head and kPa using simple conversion factors.
Pressure from a head of water (worked example)
Using pressure equals density times gravity times height to turn a head in metres into pressure.
Calculations: heating water
Calculations: flow & fill time
Calculations: pressure units
Calculations: energy & run time
Calculations: flow units
Heat transfer and thermal expansion
Conduction, convection and radiation in plumbing
The three ways heat moves and where each one shows up in plumbing and heating.
Fabric heat loss through a wall (worked example)
Using U times A times temperature difference to find the heat lost through a building element.
Thermal expansion of a pipe run (worked example)
A worked example of how much a metal pipe lengthens when heated, and why it must be allowed for.
Write the units before using a plumbing formula
For plumbing science questions, identify the quantity you need and convert the inputs before substituting numbers. Explain whether the answer is a pressure, energy, power or time. A plausible number with the wrong unit can conceal an incorrect method.
Use the head-to-pressure calculator and water heat-up calculator to check your working. The plumbing aptitude-test guide also covers the measurement, ratios and arithmetic useful when starting training.
More Plumbing modules
Every module has its own revision notes and question bank.