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# A.3.4 Pressure Drop Per 100 Feet Method

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This sizing
method is less conservative than the others, but it allows the
designer to immediately see where the largest pressure drop
occurs in the system. With this information, modifications
can be made to bring the total drop to the critical

Follow the procedures described in the Longest Length Method for Steps (1) through (4) and (9).

For each

For example, if it is desired to get flow through

For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm.

*appliance*within the limitations that are presented to the designer.

Follow the procedures described in the Longest Length Method for Steps (1) through (4) and (9).

For each

*piping*segment, calculate the pressure drop based on pipe size, length as a percentage of 100 feet (30 480 mm) and gas flow. Table A.3.4 shows pressure drop per 100 feet (30 480 mm) for pipe sizes from

^{1}/

_{2}inch (12.7 mm) through 2 inches (51 mm). The sum of pressure drops to the critical

*appliance*is subtracted from the supply pressure to verify that sufficient pressure will be available. If not, the layout can be examined to find the high drop section(s) and sizing selections modified.

**Note:**Other values can be obtained by using the following equation:

For example, if it is desired to get flow through

^{3}/

_{4}-inch (19.1 mm) pipe at 2 inches/100 feet, multiply the capacity of

^{3}/

_{4}-inch (19.1 mm) pipe at 1 inch/100 feet by the square root of the pressure ratio:

PRESSURE DROP PER 100 FEET IN INCHES w.c |
PIPE SIZES (inch) | |||||

^{1}/_{2} |
^{3}/_{4} |
1 | 1^{1}/_{4} |
1^{1}/_{2} |
2 | |

0.2 | 31 | 64 | 121 | 248 | 372 | 716 |

0.3 | 38 | 79 | 148 | 304 | 455 | 877 |

0.5 | 50 | 104 | 195 | 400 | 600 | 1160 |

1.0 | 71 | 147 | 276 | 566 | 848 | 1640 |

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