#### Mr.ZippyTheSquirrel

##### New Member

Using this table

IFGC TABLE 402.4(2)/IRC TABLE G2413.4(1) SCHEDULE 40 METALLIC PIPE Gas Natural Inlet Pressure Less than 2 psi Pressure Drop 0.5 in. w.c. Specific Gravity 0.60

Using the accepted Longest Run Method, the capacity at then end of 80' of 3/4" pipe would be 117 cubic feet per hour (ft3/hr).

I am thinking that it should be calculated by first determining the capacity available at the end of 40' of 1" pipe, which is 320 ft3/hr. Then determining the percentage drop in capacity of 3/4" pipe during the first 30' of pipe. Since the table doesn't show a value for capacity at 0 ft, the best that can be done would be between 10' and 40' (so 30' total) [(170-360)/360] which gives a 52.78% decrease. Applying this decrease to the originally calculated 320 ft3/hr results in [(100%-52.78%)*320] 151 ft3/hr.

This 151 seems much more reasonable than 117 ft3/hr.

Please help me understand what is correct.

Interestingly enough, I calculated the percentage pressure drop of 3/4" pipe between 50' and 80' [(117-151)/151] which gives a 22.52% decrease. Applying this decrease to the originally calculated 320 ft3/hr results in [(100%-22.52%)*320] 247.9 ft3/hr.

I feel like I am certainly not understanding something. Any assistance is greatly appreciated.