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Unit 004SCIENTIFIC PRINCIPLES
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Section1
Measurements used in
Mechanical Services
Measurement
(The S.I. Metric system)
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WHAT ARE WE GOING TO COVER
TODAY?
THE S.I. UNITS OF MEASUREMENTS USED IN PLUMBING
Measurement
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Measurement
The S.I. system is the system that has been adopted for
the U.K.
from existing metric systems.
S.I. Stands forSysteme Internationale.
The construction industry uses Sub units milli but NOT
the centi. i.e. millimetres, but not centimetres.
However, since the introduction of metrication, the centiis becoming increasingly popular.
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Measurement
1 Metre = 1000 millimetres (mm)
1 Bar = 1000 millibars (mb)
1 Bar also equals 100 kilo pascal (Kpa)
1 kilo pascal (Kpa) = 1 kilo Newton per meter squared (1kN/m2
) 1 Kilogram = 1000 grams (g)
1 sq. metre = 1,000,000 sq. millimetres
1 Bar = 10 meters of head
NB Milli = one thousandth of
Kilo = one thousand times
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Measurement
TIME IS MEASURED IN;
Hours, Minutes and Seconds (s)
1hr = 60mins 1min = 60 seconds
3600 seconds = 1hr (60x60 = 3600)
Seconds (s) are the preferred method
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HEAT AND TEMPERATURE
Measurements
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Measuring Temperature
Latent Heat
Thermal expansion
Heat and Temperature
TEMPERATURE
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Heat and Temperature
The main difference between heat and temperature is that heat is
recognised as a unit of energy, measured in joules.
temperature is the degree of hotness of a substance
heat is the amount of heat energy (j) that is contained within asubstance.
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An example of this which is shown in a number of text
books is a short length of Steel wire heated until it is
red hot and a bucket of hot water.
The temperature of the wire is 350C
The water has a temperature of70C
The wire is far hotter, but actually contains less
heat energy.
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Heat and Temperature
The S.I. unit of temperature measurement is the
degree Kelvin, the most common unit used in
plumbing is degrees Celsius (centigrade) written as C
An other unit used is Fahrenheit, it is some times
necessary to convert from one scale to an other.
MEASURING TEMPERATURE
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Heat and Temperature
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Temperature scale
The difference between two fixed points is divided
into 100 equal parts, each called a degree. The ice
point is 0C and the steam point 100C. This method
was devised by a Swedish astronomer named Celsius,
and is now called the Celsius scale.
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Heat and Temperature
The Kelvin scale like Celsius uses single degree
increments but the freezing point is 273.15k and the
boiling point 100 degrees higher at 373.15k
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Heat and Temperature
Absolute zero is theoretically the lowest possible
temperature that can ever be reached. To convert
from C to k add 273.15 and to convert from k to C
subtract 273.15. no temperature in Kelvin is negative
but Celsius is negative when it drops below 0C
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Heat and Temperature
Converting to Fahrenheit
Celsius Location Fahrenheit
0 Freezing point of (water) 32
4 Maximum density (water) 39.2
20 Average room temperature 68
36.8 Blood temperature 98.4
43.3 Bath water 110
60 Washing-up water 140
65 Primary return 149
85 Primary flow 185
100 Boiling point (water) 212
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Heat and Temperature
Converting to Fahrenheit using mathematics
Fahrenheit has 180 divisions and starts at 32
Celsius has 100 divisions and starts at 0
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Heat and Temperature
This means that 9 divisions in Fahrenheit are equalto 5 divisions Celsius
To put it an other way 1 degree Celsius is 95times
greater than 1 degree Fahrenheit
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Heat and Temperature
As Fahrenheit starts at 32. Therefore the formula for
converting from Fahrenheit to Celsius is Degrees
Celsius = Degrees Fahrenheit32 x 59
The formula for converting from Celsius to Fahrenheit
is Degrees Fahrenheit = Degrees Celsius x 9 + 32
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Heat and Temperature
WORKED EXAMPLE
Convert 212 Fahrenheit to degrees Celsius
Degrees Celsius = degrees Fahrenheit 32 x 5
9Degree Celsius = 212 32 x 5
9
Degree Celsius = 180 x 59
Degree Celsius =100C 212F = 100 C
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Heat and Temperature
Worked example
Convert 20 Celsius to degrees Fahrenheit
Degrees Fahrenheit = degrees Celsius x 9 + 32
5Degrees Fahrenheit = 20 x 9 + 32
5
Degrees Fahrenheit = 4 x 9 + 32
Degrees Fahrenheit = 36 + 32
Degrees Fahrenheit = 68 C 20 C = 68 F
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Heat and Temperature
We have looked at the complicated method, lets now
look at the simpler method,
Celsius to Fahrenheit = (C x 1.8) + 32 = F
Fahrenheit to Celsius = (F 32) x 0.56 = C
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Heat and Temperature
Convert 212 Fahrenheit to degrees Celsius
Degrees Celsius = (F 32) x 0.56 = C
Degrees Celsius = (212-32) x 0.56
Degrees Celsius = 100.8 C
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Heat and Temperature
Convert 20 Celsius to degrees Fahrenheit
Celsius to Fahrenheit = (C x 1.8)+ 32
Degrees Fahrenheit =(20 x 1.8)+ 32
Degrees Fahrenheit = 68 F
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Heat and Temperature
Devices used to measure temperature
Now see
SmartScreenWorksheet 8
Temperature
measurement
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Heat and Temperature
There are three forms of state in which a substance
can exist,
Solid
Liquid
Gas
LATENT HEAT
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Heat and Temperature
Water exits in three states ice (solid), water (liquid),
gas (steam).
The change of state from solid to liquid or vice versa is
termed the lower change of state andthe change
from a liquid to a gas istermed theupper change of
state
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Heat and Temperature
Heat that brings about a change in state with no
change in temperature is called latent (hidden) heat.
When a substance changes state the temperature
stays the same. It is the addition or removal of the
heat that produces the change of state.
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Heat and Temperature
Heat which causes a change in temperature in asubstance is called sensible heat.
When ice turns to water it is changing state from a solidto a liquid. In order to achieve this the ice requires
additional heat energy. The heat being applied to the ice
is used to change state. During this period there is no
increase in temperature, although the heat is still being
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Heat and Temperature
When the ice has completely turned to water, the
temperature will begin to rise again. When the ice has
completely turned to water, the temperature will
begin to rise again.
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Heat and Temperature
When the reverse happens I.e. water turns to ice, the
change of state being liquid to solid, there is a surplus
of energy I.e. heat energy is given off. This counteractsthe cooling effect and there is no drop in temperature
until all the water has turned to ice, the temperature
then continues to drop.
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Heat and Temperature
This happens whenever a substance changes state, so
it will also happen when water turns to steam. I.e. the
temperature of the water will reach 100 C, but will
not increase until the water has turned to steam.
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Heat and Temperature
In reverse, the steam will turn to water and during
this time, the temperature will not fall until all the
steam has turned to water. During this time latent
heat is given off.
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Heat and Temperature
Ice
to
water
A B C D E
100
0
Water to steam
Heat input joules
TemperatureC
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Heat and Temperature
Now in your own words on the note page provided
sum up the following terms,
MELTING
FREEZING
BOILING
EVAPORATING / EVAPORATION
CONDENSING35
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Heat and Temperature
From point A to point B the temperature is rising
steadily. The heat being absorbed during this period is
called sensible heat because it can be sensed by the
thermometer. From B to C it is apparent that heat is
still being absorbed but it is not visible on the
thermometer
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Heat and Temperature
From B to C it is apparent that heat is still being
absorbed but not visible on the thermometer, so it is
called latent heat because it cannot be seen.
From C to D the thermometer shows the second
increase in sensible heat and from D to E shows
latent heat again.
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Heat and Power
Recovery Rate
This is the
amount of time
required to heatup a quantity of
water to a
specifictemperature
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Heat and Power
Heat Recovery Period
This time will vary depending upon the heat source
power rating.
It is possible to calculate the heat recovery period.
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Measurement (RECAP)
TIME IS MEASURED IN;
Hours, Minutes and Seconds (s)
1hr = 60mins
1min = 60 seconds
3600 seconds = 1hr (60x60 = 3600)
Seconds (s) are the preferred method
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Heat and Power
Using this formula:
SH x Kg x temperature riseAvailable time in seconds
SH = the specific heat of water(the amount of
energy required to heat 1kg of water by 1C)
Kg = the weight of water to be heated
= Power Required
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Heat and Power
Example: Find the power required to heat a cylindercontaining 100 litres of water to 60C
Incoming water supply temperature = 4C
Customer requires water, to be at 60C, in 1hours
SH x Kg x temperature rise
Available time in seconds
= Power Required
4.2 x 100 x 56 23520
90 x 60 5400
= = 4.36 kW
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Heat and Power
This example does not allow for heat loss and the heating-up of the
HWSC. It is advisable to add 10% which will allow for this loss.
e.g. 4.36 + 10% =4.36 +
0.43
4.79 kW
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Heat and Power
Example: Find the power required to heat a cylinder containing
125 litres of water to 60C
Incoming water supply temperature = 18C
Customer requires water, to be at 60C, in hour
SH x Kg x temperature rise
Available time in seconds
= Power Required
4.2 x 125 x 4 2 22050
30 x 60 1800=
= 12.25 kW
+ 1.22 10%
13.47 kW
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Heat and Power
Often the house owner will want to know how long it
should take to heat a cylinder of water.
This can also be found using the same formula with a
bit of transposition:
SH x Kg x temperature rise
Available time in SecondsPower (kW)
= time in secondsPower Required
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Heat and Power
Often the house owner will want to know how long it
should take to heat a cylinder of water.
This can also be found using the same formula with a
bit of transposition:
SH x Kg x temperature risePower Required = time in seconds
SH x Kg x temperature rise
Available time in seconds
= Power Required
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Heat and Power
Example: Find out how long it will take to heat a cylinder containing
136 litres of water to 60C, using the 3kW immersion heater.
Incoming water supply temperature = 4C
SH x Kg x temperature rise
Power (kW)= time in seconds
4.2 x 136 x 56
3 = 10662 seconds
= 177 minutes = 2 hrs 57mins10662
60 47
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Heat and Power
Example: Find out how long it will take to heat a cylinder containing
150 litres of water to 60C, using the 27kW gas boiler.
Incoming water supply temperature = 13C
SH x Kg x temperature rise
Power (kW)= time in seconds
4.2 x 150 x 47
27 = 1097 seconds
= 18 minutes1097
60 48
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Heat and Power
Example: Find the power required to heat a cylinder containing 130
litres of water to 60C.Incoming water supply temperature = 12C
Customer requires water to be at 60C, in 1hour
Example: Find out how long it will take to heat a cylinder containing 115litres of water to 60C, using the 23kW gas boiler.
Incoming water supply temperature = 5C
Example: Find out how long it will take to heat a cylinder containing 120litres of water to 60C, using the 3kW immersion heater.
Incoming water supply temperature = 14C
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Heat and Power
Example: Find the power required to heat a cylinder containing130 litres of water to 60C.
Incoming water supply temperature = 12C
Customer requires water, to be at 60C, in 1hour
SH x Kg x temperature rise
Available time in seconds= Power Required
4.2 x 130 x 48 262081 x 60 x 60 3600
== 7.28 kW
+ 0.72 10%
8.00 kW
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Heat and Power
Example: Find out how long it will take to heat a cylinder containing
115 litres of water to 60C, using the 23kW gas boiler.
Incoming water supply temperature = 5C
SH x Kg x temperature rise
Power (kW)
= time in seconds
4.2 x 115 x 55
23 = 1155 seconds
= 19 minutes1155
60
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Heat and Power
Example: Find out how long it will take to heat a cylinder containing
120 litres of water to 60C, using the 3kW immersion heater.
Incoming water supply temperature = 14C
SH x Kg x temperature rise
Power (kW)= time in seconds
4.2 x 120 x 46
3
= 7728 seconds
= 129 minutes = 2 hrs 9mins7728
60
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Heat and Power
SPECIFIC HEAT CAPACITY
The specific heat capacity of a substance or material is
the amount of heat required to raise the temperature
of1kg of the material by 1C. the heat required varies
depending on the material.
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Heat and Power
E.g. the heat required to raise 1kg of water by 1C is
4.186kJ and 0.125kJ would be required to raise 1kg of
lead by 1C
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Material kJ/kgC
Water 4.186
Aluminium 0.887
Cast Iron 0.554
Zinc 0.397
Lead 0.125
Copper 0.385
Mercury 0.125
Heat and Power
Specific Heat Capacity Values
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HEAT TRANSFER
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Heat and Power
There are three methods of heat transfer :
Conduction
Convection
Radiation
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Heat and Power
Conduction
Conduction is the transfer of heat energy through a
material. This happens because of the increased
vibration of molecules, which occurs when materialsare heated.
The vibrations from the heated material are then
passed on to the adjoining material, which then heatsup in turn.
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Heat and Power
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Heat and Power
Some materials are better conductors than others
Metals tend to be good conductors
Wood is a poor conductor of heat
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Heat and Power
Copper is a better conductor of heat than steel, ironand lead. Wood plastics which are poor conductors of
heat are known as thermal insulators
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Heat and Power
Convection
Convection is the transfer of heat by means of movement of a
locally heated fluid substance (usually air or water). As fluid is
heated the process causes expansion which in turn causes a
lowering of its density. The less dense warm flue begins to
rise and is replaced by cooler, denser fluid from below.
Eventually convection currents are set up which allow for a
continuous flow upwards from the source.
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Heat and Power
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Heat and Power
Radiation
Radiation is the transfer of heat from a hot body to a
cooler one. It does not need a material medium to do
this. It needs only air and uses heat waves.
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Heat and Power
Radiation can be sensed on a sunny by the heat of the
sun. Some materials absorb heat radiation better
than others. Colour often plays apart, dull matt
surfaces will absorb radiation heat better than shiny
polished surfaces.
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Heat and Power
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Heat and Power
Now in your own words on the note page provided
sum up the following terms,
CONVECTION
CONDUCTION
RADIATION
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Heat and Temperature
THERMAL EXPANSION
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Heat and Temperature
Most materials will expand when heated. This
because the molecules in a substance move about
more vigorously when heated. The molecules will
then move further apart from each other, this will
mean that the materials taking up more volume.
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Heat and Temperature
When a material cools the molecules slow down and
move closer together, thus the material gets smaller
or contracts. The amount a material expands in length
can be calculated using the following formula.
Length (m) x temp rise (C) x coefficient of linear
expansion
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Heat and Temperature
Material Coefficient C
Plastic 0.00018
Zinc 0.000029
Lead 0.000029
Aluminium 0.000026Tin 0.000021
Copper 0.000016
Cast iron 0.000011
Mild Steel 0.000011
Invar 0.00000009
Now look at SmartScreen hand-out 1 & 2 Properties of materials
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Heat and Temperature
Worked Example
Calculate the amount a 4m long plastic discharge stack will expanded
due to a temperature rise of 24C.
Amount of Expansion = 4 x 24 x 0.00018*
Amount of Expansion = 0.0172m or 17.28mm
*Figure take from chart
Now look at SmartScreen hand-out 9 Expansion of liquids and work
sheet 4 Heat and power 72
PROPERTIES OF WATER
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Classification of water
Corrosion
Specific heat capacity
Heat transfer
Capillary attraction
Siphonage
PROPERTIES OF WATER
What are we going to look at?
Properties of Water
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Properties of Water
Water is a chemical compound which is made up of Hydrogen and
Oxygen (H2O). An important property of water is its solvent power.
It has the ability to dissolve some gases and solids to form
solutions.
CLASSIFICATION OF WATER
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Properties of Water
The purest form of water is rain water which is collected on the
open countryside. It contains dissolved gases such as nitrogen,
oxygen and carbon dioxide, this doesnt affect its potability
(suitability for drinking)
Water may be classified as having varying degrees of
hardness or softness
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Properties of Water
Permanent hardness occurs as a result of the natural solvency
of pure water. It will dissolve sulphates of limestone. A symptom of
hard water is the difficulty in forming a lather with soap.
Temporary hardness is responsible for the hard scale which can
accumulate on the inside of boilers, pipework and cylinders. It will
restrict the flow of water, reduce the efficiency of appliances which
can lead to system failure.
Water Hardness
Water hardness can be described as temporary or permanent.
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Properties of Water
Water that is Soft will enable a lather to be produced soap easily.
This is because of the absence of dissolved salts such as Calcium
Carbonates and Calcium sulphates.
pH Value
The term pH value refers to the level of acidity or alkalinity of a
substance. Pure water has a pH of 7.0. If water dissolves acidic
materials, the pH falls and if it dissolves alkaline materials the pH
rises.
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p
Acidic and alkaline water can both damage the materials used in
plumbing systems, by causing corrosion. Metals are particularly at
risk from corrosive effects of acids and alkalis.
Slightly acidic water will break down materials in plumbing
systems, resulting in the build up of silt and other debris in the
system.
Rainwater is naturally slightly acidic, due to small amounts of
carbon dioxide and sulphur dioxide in the atmosphere dissolved
into it, forming very weak carbonic and sulphuric acids.
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p
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p
There are four main causes of corrosion
The effects of air
The effects of water
The direct effects of acid, alkalis and chemicals.
(from environmental sources)
Electrolytic action
CORROSION
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p
Atmospheric Corrosion
Pure air and water have little corrosive effects, but together in the
form of moist air(oxygen + water vapour)they can attack ferrous*metals such as steel and iron very quickly to form iron oxide or
rust.
*Metal that contains iron
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p
The corrosive effects of rusting can completely
destroy metal
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Gases such as Carbon dioxide, sulphur dioxide and sulphurtrioxide which can be found in our atmosphere, will also increase
the corrosive effects air has on certain metals, especially iron,
steel and Zinc.
These gases are often found near industrial areas as these gases
are often waste products from various industrial processes.
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Coastal areas also suffer from increased atmospheric corrosion
due to the amount ofsodium chloride (salt) from the seawhich
become dissolved into the local atmosphere.
Non- ferrous metals such as copper, aluminium and lead, have
significant protection against atmospheric corrosion. Protective
barriers usually sulphates form on these metals to prevent further
corrosion. This protection is called a patina
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Corrosion by Water
Ferrous metals are particularly vulnerable to the effects of
corrosion caused by water. The effects of this corrosion are
commonly seen in central heating systems as black ferrous oxide
and red rust (Haematite and Magnetite) build up in radiators.
A by-product formed from this action is hydrogen gas which
accumulates in the radiators. The build up can be released by
bleeding the radiators.
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Properties of Water
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If the water in an area has a high acidity (soft water ) the internal
wall of the copper may become slightly discoloured. This will not
affect the safety or quality of the drinking water.
If there is lead pipework within a building there is a risk of the
water dissolving minute quantities of lead, this contaminating the
water. This may have toxic effect especially for children.
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The Direct Effects of Acid, Alkalis and Chemicals.
(From environmental sources)
Some types of wood (such as oak) have a corrosive effect on
lead, latex cement and formed concrete will adversely affect
copper.
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Heavy clay soils may contain sulphates which can corrode lead,
steel and copper. Grounds containing ash and cinders are also
very corrosive as they are strongly alkaline, if pipes are to be laid
in such ground they should be wrapped in protective material
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Electrolytic action is caused when two very dissimilar metals come
into contact with each other. The process involves the flow of
electrically charged ions from an anode to a cathode through a
medium known as the electrolyte (this is usually water)
ELECTROLYTIC ACTION
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This process is called electrolysis. It will lead to the destruction of
the anode. The time that it takes to destroy the anode will depend
on :
The properties of the water that acts as the electrolyte, if the
water is hot or acidic the rate of the corrosion will increase
The position of the metals that make up the anode and cathode
in the electromotive series
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The list on the next slide shows the common elements used in the
plumbing industry. The order in which they appear indicates their
electromotive properties.
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Copper Cathodic
Tin
Lead
Nickel
Cadmium
Iron
Chromium
Zinc
Aluminium
Magnesium Anodic
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The elements higher up the list will destroy those lower down
through electrolytic corrosion. The further the elements are to
each other the faster the corrosion takes place.
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This problem needs to be recognised by plumbers, especially if
metal such as copper and galvanised tube and copper fitting arein direct metallic contact. If these metallic elements are
surrounded by water or damp ground, a basic electrical cell is
created and electrolytic corrosion can take place.
Properties of Water
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Properties of Water
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Capillary attraction is when a liquid is drawn up through a small
gap between the surfaces of two materials.
Capillary attraction occurs due to two characteristics of most
liquids.
CAPILLARY ATTRACTION
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Adhesion is the ability to stick to a surface. Water in a smal tube
such as a U gauge (manometer), has a curved surface where the
water adheres to the sides of the tube. This is called the meniscus
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Meniscus
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Adhesion
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Cohesion is the ability of a liquid to pull itself into a ball. This is
also called surface tension. A simple illustration of this is
rainwater laying on a well-polished car
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Cohesion
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When planning the installation of sheet lead weathering, the affect
of capillary attraction needs to be taken into account. Water can
penetrate a building via a lapped joint, as the materials are closed
together.
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Properties of Water
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This can be avoided by installing an
anti-capillarity groove,
this will prevent water entering the building
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Capillary attraction can also take place within an S trap often
found under sinks, if a piece of dish cloth becomes lodged in tothe in the trap. Capillary attraction could take place. This can lead
to the loss of the trap seal and smells filtering back into the home
from the drains
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Properties of Water
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Principles of Siphonage
Atmospheric pressure is the key to siphonage. Siphonage works
when atmospheric pressure is able to force water through a tube
i.e. a length of hose pipe. It may appear that it is going against
the force of gravity.
For siphonage to work the air pressure in the tube must be
reduced below that of atmospheric pressure.
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Properties of Water
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Siphonic Wcs
Common uses of symphonic action are found
on Wcs
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Properties of liquids and gases
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p q g
Liquids used in Mechanical services consist of:
Water
Refrigerant
Anti- freeze- glycol mixes
Fuel oils
Lubricants / Greases
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p q g
WATER
Widely used in the industry.
IE Cold water, Hot water, Heating, Etc.
H20- Hydrogen 2 parts and oxygen 1 part.
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p q g
REFRIGERANT
Used in Air conditioning, freezers and fridge
units and heat pumps.
Mixture of chemicals and gasses in order to
perform at extreme temperatures
Data sheets for refrigerants
Properties of liquids and gases
http://localhost/var/www/apps/conversion/tmp/scratch_4//Staff06/data/dshare/FACULTY%20OF%20CONSTRUCTION/PLUMBING/COURSES%20WE%20ARE%20TEACHING%20TEACHING/COURSES/NVQ%20DIP%20PLUMBING%20AND%20DOM%20HEATING/LEVEL%202/Theory/Unit%20004%20-%20Scientific%20Principles/Data%20sheets%20for%20.%20refrigerants.htmhttp://localhost/var/www/apps/conversion/tmp/scratch_4//Staff06/data/dshare/FACULTY%20OF%20CONSTRUCTION/PLUMBING/COURSES%20WE%20ARE%20TEACHING%20TEACHING/COURSES/NVQ%20DIP%20PLUMBING%20AND%20DOM%20HEATING/LEVEL%202/Theory/Unit%20004%20-%20Scientific%20Principles/Data%20sheets%20for%20.%20refrigerants.htm -
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ANTI- FREEZE / GLYCOL MIXES
Used in solar thermal panels, combustion
engines, Etc.
Mixture of chemicals in order to perform at
extreme temperatures
Product data sheet
Properties of liquids and gases
http://localhost/var/www/apps/conversion/tmp/scratch_4//Staff06/data/dshare/FACULTY%20OF%20CONSTRUCTION/PLUMBING/COURSES%20WE%20ARE%20TEACHING%20TEACHING/COURSES/NVQ%20DIP%20PLUMBING%20AND%20DOM%20HEATING/LEVEL%202/Theory/Unit%20004%20-%20Scientific%20Principles/Glycol%20mix%20.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_4//Staff06/data/dshare/FACULTY%20OF%20CONSTRUCTION/PLUMBING/COURSES%20WE%20ARE%20TEACHING%20TEACHING/COURSES/NVQ%20DIP%20PLUMBING%20AND%20DOM%20HEATING/LEVEL%202/Theory/Unit%20004%20-%20Scientific%20Principles/Glycol%20mix%20.pdf -
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FUEL OILS & Lubricants / Greases
Fuel oils are mainly used for heating purposes,
however majority of mechanical moving parts
require an oil or grease as a lubricant.
Carbon Based non renewable taken from the
earth and refined into the above products at
various levels
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Gases used in Mechanical services consist of:
Air and steam
LPG Liquid Petroleum Gas
Natural Gas
Carbon Dioxide
Refrigerant Gasses
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Air and Steam
These are mainly used for producing pressure in
order to drive industrial machinery.
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LPG Liquid Petroleum Gas
A gas that is used to heat homes and for cooking
in rural areas not on mains gas. You use this gas
for soldering, camping and caravan, boats etc.
Factories may use this for localised heating.
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Natural Gas
Supplied from the gas mains, and currently the
most common gas used for heating buildings,
both domestic and industrial.
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Carbon Dioxide
Carbon dioxide in solid and in liquid form is used
for refrigeration and cooling. It is used as an
inert gas in chemical processes, in the storage ofcarbon powder and in fire extinguishers.
Pipe freezing kits may use this gas.
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Refrigerant Gases
Used in Air condition, freeze and fridge units
and heat pumps.
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Mass and weight
Density liquids and gases
Relative density
Pressure
g
What are we going to look at?
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Temperature of Gases.Properties of Gases
(Typical Values)
Quality/Unit Natural Methane Propane Butane
Chemical Formula CH4 C3H8 C4H10
Boiling Point -1620C -420C -20C
Relative Density (Liquid) - 0.5 0.57
Relative Density ( Gas) 0.58 1.78 2.0
Gross Calorific Value 38.5MJ/m3 95MJ/m3 121MJ/m3
Gas Family 2nd 3rd 3rd
Flammability Limits 5-15% 2.3-9.5% 1.9-8.5%
Air/Gas Ratio 9.81:1 23.8:1 30.9:1
Oxygen/Gas Ratio 2:1 5:1 6.5:1
Flame Speed 0.36m/s 0.46m/s 0.38m/s
Ignition Temperature 7040C 5300C 5000C
Maximum Flame Temp. 10000C 19800C 19960C
System Operating Pressure
21mb (+/- 2) 37mb (+/-5) 28mb (+/- 5)
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Gas Laws:
Charless Law At constant pressure, the volume of a given mass of an ideal gas increases or decreases
by the same factor as its temperature on the absolute temperature scale (i.e. the gasexpands as the temperature increases).[1]
Boyles LawBoyle's law (sometimes referred to as the BoyleMariottelaw) states that the absolute pressure and volume of a given mass of confinedgas are inversely proportional, if the temperature remains unchanged within a
closed system.[1][2]
Boyles Law 2
Properties of gasses
http://www.youtube.com/watch?v=IkRIKGN3i0khttp://en.wikipedia.org/wiki/Absolute_temperature_scalehttp://www.youtube.com/watch?v=J_I8Y-i4Axchttp://en.wikipedia.org/wiki/Pressurehttp://en.wikipedia.org/wiki/Volumehttp://en.wikipedia.org/wiki/Temperaturehttp://en.wikipedia.org/wiki/Closed_systemhttp://www.google.co.uk/imgres?imgurl=http://upload.wikimedia.org/wikipedia/commons/thumb/1/15/Boyles_Law_animated.gif/220px-Boyles_Law_animated.gif&imgrefurl=http://en.wikipedia.org/wiki/Boyle%27s_law&h=167&w=220&sz=210&tbnid=KZ4zZ_spLXnNqM:&tbnh=90&tbnw=119&prev=/search?q=boyles+law&tbm=isch&tbo=u&zoom=1&q=boyles+law&docid=rdA0z9EZwxqKHM&hl=en&sa=X&ei=ltYGT8WCNYSv8QPtt7DoCQ&ved=0CFgQ9QEwBg&dur=1152http://www.google.co.uk/imgres?imgurl=http://upload.wikimedia.org/wikipedia/commons/thumb/1/15/Boyles_Law_animated.gif/220px-Boyles_Law_animated.gif&imgrefurl=http://en.wikipedia.org/wiki/Boyle%27s_law&h=167&w=220&sz=210&tbnid=KZ4zZ_spLXnNqM:&tbnh=90&tbnw=119&prev=/search?q=boyles+law&tbm=isch&tbo=u&zoom=1&q=boyles+law&docid=rdA0z9EZwxqKHM&hl=en&sa=X&ei=ltYGT8WCNYSv8QPtt7DoCQ&ved=0CFgQ9QEwBg&dur=1152http://en.wikipedia.org/wiki/Closed_systemhttp://en.wikipedia.org/wiki/Temperaturehttp://en.wikipedia.org/wiki/Volumehttp://en.wikipedia.org/wiki/Pressurehttp://www.youtube.com/watch?v=J_I8Y-i4Axchttp://en.wikipedia.org/wiki/Absolute_temperature_scalehttp://www.youtube.com/watch?v=IkRIKGN3i0k -
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Heat pump / Refrigeration cycle
Drawing and stages
Plumbing Science
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Mass in its simplest terms is the amount of matter in an object. It is
measured in grams or kilogram's. An objects mass will stay the same
unless parts are removed from it.
A basin tap will have the same mass, if it is on a work bench or on the
moon.
MASS
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The weight of an object is the force exerted by its mass, due to the
acceleration owing to force ofgravity.
On the earth all objects are being accelerated towards centre of the
planet. This is due to the earths gravitational pull.
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Pull exerted by gravity on mass of an object is known as its weight . We
measure weight in Newton's.
A Newton is equivalent to
1 metre per second (m/s2) per 1kg of mass.
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On the Earth
The gravitational pull of the earth is 9.8m/s2
Therefore, an object with a mass of1kg on earth
would weigh 9.8 newtons
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On the moon
The gravitational pull of the moon is approximately 1.633m/s.
An object with a mass of1kg on the moon - would weigh 1.633
newtons.
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Mass of the object does not change whether it is on earth or on the
moon, but weight of an object changes immensely due to the reduced
gravitational pull of the moon.
Solid materials which have the same shape, can frequently have a
completely different mass. This is know as is density. The density of an
item is measured by its mass compared to its volume
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To calculate this the following formula is used
Density = mass
volume
Liquids and gases also have different densities, dependent on thenumber of molecules present within a particular volume of a
Substance.
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It is also very important to understand that the density of water changes
when temperature of water changes. Water is less dense when heated.
1m3 of water at 4C has a mass of 1000Kg
1m3 of water at 82 C has a mass of 967Kg
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Air
Polystyrene
Lead
Mass of all cubes are the same but volumes are different. Leadwill occupy a smaller volume than both air and the polystyrene,
due to its molecules being more tightly packed
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A mass that is concentrated in a smaller volume has a greater density
than a substance of equal mass that occupies a larger space.
Thus, gases have the smallest densities when compared to solids and
liquids. Gas molecules contain mostly empty space, while molecules in
liquids, are again more tightly packed together.
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Relative density (also known as specific gravity), is an effective way ofmeasuring the density of a substance or object and comparing its
weight per volume to an equal volume of water.
RELATIVE DENSITY
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1m3
of water has a mass of1000kg at 4C whereas 1m3
of lead weighsabout 11300kg. From this it can be seen that lead is 11.3 times heavier.
Knowing this, we can calculate weight of any substance by dividing
density of a substance by the density of water.
Water is always shown as 1.0
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Using this information, we know that any material with a higher numberthan 1.0 will sink in water and any number lower will float.
The relative density of gases can also be measured by comparing the
specific gravity of air, which is also expressed as 1.0
Material Relative density
Solids and Liquids
1 0
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Water 1.0
Class C fuel oil 0.79
Linseed oil 0.95
Aluminium 2.7
Zinc 7.1
Cast iron 7.2
Tin 7.3
Mild steel 7.7
Copper 8.9
Lead (Milled) 11.3
Mercury 13.6
Gases
Air 1.0
Methane ( Natural Gas) 0.6
Propane 1.5
Butane 2.0
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4c
10c
4c
1c
Maximum density of water 4C
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Relative Density of
Materials
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As water is heated, the process causes expansion, in - turn causes alowering density. The less dense warm water begins to rise, replaced by
cooler, denser fluid from below.
Eventually convection currents are set up, allowing a continuous flow of
heat upwards from its source.
Principles of mechanical advantage
and velocity ratios
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and velocity ratios.
Levers: What is a lever?In Basic form of a lever is a steel rod known as a
crowbar.
Wheel and axle: What is this?
In basic form a good example would be a car
steering wheel.
Principles of mechanical advantage
and velocity ratios
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and velocity ratios.
Pulleys: What is this? A pulley is an arrangement of wheels with a
rope passed through them to enable the
movement of heavier objects. (block andtackle)
Principles of mechanical advantage
and velocity ratios
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and velocity ratios.
Screws: What is this? A screw is used to lift an item under tension,
an example of this could be a acro .prop
Principles of basic mechanics
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Theory of moments.
Action and reaction.
Centre of gravity.
Equilibrium.
Using the Pcs Reach the above.
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Force will try to move an object
We cannot see force, however its effects can be seen in the next slide
FORCE
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Force
Force
Force is the cause of a
change in shape
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The unit of measurement for force is the Newton (N)
An object weighing 1 kg, dropped from a height, will travel at an
acceleration of 9.81 metres/second squared (m/s2) due to the earths
gravitational pull (gravity)
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Force = Mass x accelerationForce = 50kg* x 9.81m/s2
Force = 490.5N
* 1Litre of water weighs 1kg
50kg
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Pressure can be defined as force acting over a specified area
Pressure is to act upon a wide variety of liquids and gasses in plumbing
applications e.g. air, water and oil. Pressure is involved in the delivery of
water that affects us most in plumbing.
PRESSURE
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Plumbing Science
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Pressure is measured in newtons per square metre (N/m2)
It is also known as Pascal (Pa)
You may have come across other terms used to identify pressure they
include (Bar or Pounds per square inch (ibs/in2)
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Static Pressure
Water will find its own level when exposed to atmosphere and with no
flow(static).
This occurs, what ever shape of the vessel in which water is placed, and
a result of gravitational force acting downwards on the water.
1 bar = 100,000N/m2 1lbs/in2 = 6894N/m2
Atmospheric pressure at sea level is 101,325N/m2
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Pressure is exerted by solid objects in downwards
direction only, however, liquids exert pressure downwards
and sideways.
Plumbing Science
There are basically two ways of creating pressure in plumbing
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There are basically two ways of creating pressure in plumbing
systems:1. By connecting a pump into the system pipe-work; or
2. By using the weight of the water itself.
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The higher the column of water (plumbers call this head of
water) the greater pressure exerted at its lowest point.
Now look at SmartScreen hand-out 3 Water Pressure and Work
sheet 6 & 7
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Intensity of pressure or static pressure can be defined as force (KPa)
created by the weight of a given mass of water acting upon one unit
area (1m2).
Example:
Intensity of pressure = head x 9.18 KPa (gravitational force)
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Total Pressure is the intensity of pressure
multiplied by the area acted on.
Example:
Total pressure = intensity of pressure x area of base
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Now look at SmartScreen worksheet
3 Plumbing Materials