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

2-2Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Puffett, Hossack, Stone, Burn & Miles, Gasfitting 2e

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.

2-3Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Puffett, Hossack, Stone, Burn & Miles, Gasfitting 2e

Pressure test equipment (1)

Manometer Pressure gauge

2-4Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Puffett, Hossack, Stone, Burn & Miles, Gasfitting 2e

Pressure test equipment (2)

Pressure recorder

2-5Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Puffett, Hossack, Stone, Burn & Miles, Gasfitting 2e

Reading a manometer

U-shaped tube and measuring scale.

One side connected to gas test point.

One side open to atmosphere.

2-6Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Puffett, Hossack, Stone, Burn & Miles, Gasfitting 2e

Manometer types

Indirect reading Direct reading

2-7Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Puffett, Hossack, Stone, Burn & Miles, Gasfitting 2e

Working pressure

This is the pressure

recorded when gas is

being used.

2-8Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Puffett, Hossack, Stone, Burn & Miles, Gasfitting 2e

Static pressure

This is the pressure

recorded when no

gas is being used.

2-9Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Puffett, Hossack, Stone, Burn & Miles, Gasfitting 2e

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)

2-10Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Puffett, Hossack, Stone, Burn & Miles, Gasfitting 2e

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.

2-11Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Puffett, Hossack, Stone, Burn & Miles, Gasfitting 2e

Absolute pressure

Absolute pressure is gauge pressure plus atmospheric pressure.

E.g. gauge pressure 1 kPa +

atmospheric pressure 101 kPa

absolute pressure = 102 kPa

2-12Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Puffett, Hossack, Stone, Burn & Miles, Gasfitting 2e

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.

2-13Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Puffett, Hossack, Stone, Burn & Miles, Gasfitting 2e

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.

2-14Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Puffett, Hossack, Stone, Burn & Miles, Gasfitting 2e