1. Plumbing science
What you need to know

2. Units of measurement
• In the UK we use two main systems of
measurement - imperial and metric
• The standard international system is
known as SI units

3. Mass and weight
• Mass is constant everywhere in the
universe. Weight changes from place to
place
• A nail will keep the same mass wherever it
is: on a workbench or on the moon

4. Density of solids
• Solid materials that have the same shape
and size can have a different mass
• This lightness/heaviness is known as
density
• Density = mass ÷ volume

5. Density of liquids
• Liquids and gases also have different
densities
• It is important to understand the density of
water
• Water is less dense when heated

6. Water
At 4˚C water is said to have a density of 1.0
Amount Temp. Mass
1m³ 4˚C 1000 kg
1m³ 82˚C 967 kg

7. Relative density
(specific gravity)
• Measures the density of a subject compared to
water
• 1m³ of water has a mass of 1000 kg
• 1m³ of mild steel has a mass of 7700 kg
• Mild steel’s relative density (density compared
to water) is 7.7

8. Density of gases
• With gases, air is given the relative
density of 1.0
• Is helium more or less dense than air?

9. Pressure
Force applied by unit area
• (N/m²) also known as (Pa)
Other terms: bar, lbs/in²
• 1bar = 100,000 N/m²
• 1 lbs/in² = 6894 N/m²

10. • Pressure is exerted by solid
objects in downwards only
• Liquid exerts pressure downward
and outward

11. Pressure exerted on all sides not just the base

12. • You will need to understand the effects
pressure has on pipes and fittings
• The internal pressure is affected by
what is being carried (water/gas)

13. Atmospheric pressure
• The pressure exerted by the earth’s
atmosphere changes as you get higher
above sea level
• At sea level it is 1 bar = 14.7 psi
• psi = lbs/in² (pounds per inches squared)

14. Properties of water
• Water is a chemical compound made from
hydrogen and oxygen (H2O)
• Water can dissolve lots of gases and solids
to produce solutions

15. Hard water
When water falls on ground that has
calcium carbonates or sulphates (chalk,
limestone or gypsum) in it, they dissolve
into a solution called hard water.

16. Soft water
Has no dissolved salts like calcium
carbonates/sulphates.

17. pH value and corrosion
• pH is the level of acidity or alkalinity of a
substance.
• Acids and alkalis can cause corrosion,
metals are more at risk

19. Atmospheric corrosion
• Pure air or water alone are not very corrosive
• Together as moist air they attack ferrous
metals (rusting)
• Other things in the atmosphere increase the
corrosive effect, eg salt, carbon dioxide,
sulphur

20. Non ferrous metals
• Copper, lead, aluminium
• These have protective barriers (usually
sulphates) which prevent further
corrosion. This happens after
oxidisation.
• This is known as patina

21. Corrosion by water
• Ferrous metals are more likely to be
corroded by water
(think of black sludge in radiators (ferrous
oxide))
• Ferrous oxide and rust combine to make
hydrogen

22. The difference between heat
and temperature
• Heat is a unit of energy measured in
Joules (J). It is the amount of heat energy
in a substance.
• Temperature is measured in centigrade
and is the degree of hotness of a
substance.

23. • The wire has a temperature of 350˚C
• The water has a temperature of 70˚C
• The wire is far hotter, but has less energy

24. Thermometers
• A bi-metallic strip is used to convert a
temperature change into movement
• Liquid thermometers use mainly alcohol
and mercury

25. Specific heat capacity
• The amount of heat needed to raise 1kg
of material by 1˚C.
• It takes 4.186 kJ to raise the temperature
of water by 1˚C, but only 0.385kJ to raise
the temperature of copper by 1˚C.

26. Specific heat capacity
• Work out the amount of heat needed to
increase the temperature of 250g of water
from 20o
C to 56o
C.

27. Specific heat capacity
q = m x Cg x (Tf - Ti)
m = 250g
Cg= 4.18 J o
C-1
g-1
(from table above)
Tf = 56o
C
Ti = 20o
C

28. Specific heat capacity
q = 250 x 4.18 x (56 - 20)
q = 250 x 4.18 x 36
q = 37 620 J = 38 kJ

29. Thermal expansion and
contraction
These are known as coefficient values
Lead has a higher coefficient value than,
say, copper ie it will move more when
warm.

31. Plumbing materials
• Plastic has coefficient value of
0.00018
• So if we had a 6m long guttering we
can work out how much it will expand
at 19°c!
• To do this we need three values

32. 1 Length (meters)
2 Temperature rise(°c)
(19 degrees is used as
standard temp rise)
3 Coefficient value

33. SoSo 66 (m) X (Temp rise)(m) X (Temp rise)1919°c°c XX
(coefficient value)(coefficient value) 0.00018 =0.00018 =
6 x 19 x 0.00018 = 0.02052m or6 x 19 x 0.00018 = 0.02052m or
20.52mm20.52mm

34. Heat transfer
• Conduction
• Convection
• Radiation

35. Conduction
The transfer of heat energy through a
material

36. Convection
The less dense air
(hotter) rises and
the denser air
(cooler) falls

37. Radiation

38. Radiators only radiate 15% of the heat. The rest
is done by convection.

39. Radiation is the transmission of heat
energy by infrared radiation.
In conduction, the excited vibrational
states of molecules are transmitted.
Convection is the circulation of hot gases.
Radiation