2-1
Chapter 2PRESSURE AND THE
MEASUREMENT OF PRESSURE
Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Puffett, Hossack, Stone, Burn & Miles, Gasfitting 2e
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Pressure
Pressure provides the energy for the distribution of gas and correct operation of burners.
The measurement of gas pressure in Australia is expressed in Pascals (Pa).
Appliances are usually rated in kilopascals (kPa).
Older appliances or those from overseas may have different ratings, e.g. inches water column, millibars (mbar), pounds per square inch (psi).
Reading and using pressure gauges
Pressure classification
– Low pressure: up to and including 7 kPa
– Medium pressure: over 7 kPa up to 200 kPa
– High pressure: over 200 kPa up to and including 1050 kPa
Most appliances are tested and approved to operate within the low pressure classification range.
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Pressure test equipment (1)
Manometer Pressure gauge
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Pressure test equipment (2)
Pressure recorder
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Reading a manometer
U-shaped tube and measuring scale.
One side connected to gas test point.
One side open to atmosphere.
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Manometer types
Indirect reading Direct reading
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Working pressure
This is the pressure
recorded when gas is
being used.
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Static pressure
This is the pressure
recorded when no
gas is being used.
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Atmospheric pressure
Atmospheric pressure is exerted by the weight of a column of air approximately 11.25 km high.
Atmospheric pressure = 101 kPa
(at sea level)
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Gauge pressure
When a manometer shows a pressure of 1 kPa, the actual pressure in the pipeline is actually atmospheric pressure plus 1 kPa.
For convenience the pressure is simply recorded as
1 kPa on the gauge.
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Absolute pressure
Absolute pressure is gauge pressure plus atmospheric pressure.
E.g. gauge pressure 1 kPa +
atmospheric pressure 101 kPa
absolute pressure = 102 kPa
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Leakage testing
Testing of gas installations to be carried out in accordance with local authority requirements and procedures.
Leak testing equipment to be appropriate for the pressures to be tested. Refer to AS 5601.
E.g. manometer for pressures up to 10 kPa.
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Pressure—Summary
• Pressure provides the energy for the distribution of gas and correct operation of burners.
• Pressure classifications: Low 0–7 kPa;
Medium 7–200 kPa; High 200–1050 kPa.
• Pressure test equipment—manometer; bourdon gauge.
• Working pressure.
• Static pressure.
• Atmospheric pressure.
• Gauge pressure.
• Absolute pressure.
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