The Physical Laws Relating to Gas. Boyle’s Law - Part 2

 

This law is named after Robert Boyle (1627–1691), who discovered the relationship between volume

and pressure of a gas. He found that the absolute pressure of a given mass of gas is inversely

proportional to its volume provided that its temperature remains constant (Absolute pressure =

Atmospheric pressure (1013 mbar + gauge pressure). 

                                                                             So.....

To put it simply, if the absolute pressure (gauge pressure + atmospheric pressure) on a given quantity

of gas decreases, then its volume will increase. So if the absolute pressure is increased four-fold, the

volume would be reduced to one quarter. The formula can be redefined as:

                                                                    P1V1 = P2V2

Where P1 = original pressure, V1 = original volume, P2 = final pressure and V2 = final volume.

Practical example Suppose that the supply pressure to a building is 80 mbar and the total volume

is 1 m3, if the pressure was reduced to 20 mbar the new volume of the gas would be calculated as

follows.

                                                  P1V1 = P2V2, so P1V1 ÷ P2 = V2

                           ∴ (1013 + 80) × 1 ÷ (1013 + 20) = 1.06m3an increase of6%.

Conversely, if the supply pressure is increased to 800 mbar when a new medium pressure regulator

is fitted, supplying the same 1 m3 volume of gas, and also reduced to 20 mbar, there is an interesting

result:

                                                                   P1V1 ÷ P2 = V2

                                ∴ (1013 + 800) × 1 ÷ (1013 + 20) = 1.76m3, an increase of76%

This increase is probably the reason that the gas supplier installed the regulator prior to the meter.