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Level 2 · Plumbing revision

Scientific Principles revision notes

The science behind the trade — pressure and head, heat and expansion, flow and units.

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  • 15notes, free to read
  • 108questions; 25 free to try
  • 8topics

C&G Unit 203: Hydraulics & Head Pressure

  1. Head, pressure and thermal expansionThe head/pressure rule of thumb and why heated water needs expansion provision.
  2. Plumbing science terms glossaryShort definitions of the physical-science terms that underpin plumbing and heating calculations.
  3. States of matter and density: a science glossaryMass, force, density and relative density, including the reference used for fuel gases.
  4. Static and dynamic pressure: friction loss in pipeworkHow flow resistance affects pressure, and why bore, demand and supply conditions matter when comparing readings.
  5. Water's freezing, boiling and density anomalyThe reference freeze/boil points, water's densest temperature, and why ice and steam each take up more room.

Calculations: head & pressure

  1. Converting between bar, metres head and kilopascals (worked example)Switching a pressure between bar, metres of water head and kPa using simple conversion factors.
  2. 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

  1. Energy to heat a cylinder of water (worked example)Using Q equals mass times specific heat times temperature rise, then finding heat-up time.

Calculations: flow & fill time

  1. Cistern fill time from flow rate (worked example)Turning a storage volume and a fill flow rate into a fill time, with unit conversion shown.

Calculations: pressure units

  1. Bar, millibar and kilopascal conversionsConvert common pressure units without losing a factor of ten or one thousand.

Calculations: energy & run time

  1. Power, energy and runtime calculationsUse kW, hours and kWh correctly and rearrange the relationship for runtime.

Calculations: flow units

  1. Litres per second and minute conversionsConvert flow rates and use time-volume checks to catch unit errors.

Heat transfer and thermal expansion

  1. Fabric heat loss through a wall (worked example)Using U times A times temperature difference to find the heat lost through a building element.
  2. Heat transfer in plumbing systems: conduction, convection, and radiationHow heat moves by conduction, convection and radiation through pipes, radiators, cylinders and rooms, with latent heat and insulation.
  3. 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.

Try the free plumbing-science questions after a topic, and 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.

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