// CODE SNIPPET

# A.6.5 Example 5: Calculating Pressure Drops Due to Temperature Changes

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A test

If the volume of the

Therefore, the gauge could be expected to register 18 psig (124 kPa) when the ambient temperature is 40°F (4°C).

*piping*system is installed on a warm autumn afternoon when the temperature is 70°F (21°C). In accordance with local custom, the new

*piping*system is subjected to an air pressure test at 20 psig (138 kPa). Overnight, the temperature drops and when the inspector shows up first thing in the morning the temperature is 40°F (4°C).

If the volume of the

*piping*system is unchanged, then the formula based on Boyle's and Charles' Jaw for determining the new pressure at a reduced temperature is as follows:

where: | ||

T_{1} |
= | Initial temperature, absolute (T_{1} + 459) |

T_{2} |
= | Final temperature, absolute (T_{2} + 459) |

P_{1} |
= | Initial pressure, psia (P_{1} + 14.7) |

P_{2} |
= | Final pressure, psia (P_{2} + 14.7) |

P_{2} |
= | 32.7 - 14.7 |

P_{2} |
= | 18 psig |

Therefore, the gauge could be expected to register 18 psig (124 kPa) when the ambient temperature is 40°F (4°C).

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