Average Pressure Calculator
Computes average pipeline pressure for use in flow equations. The two-thirds average (GPSA method) is preferred for compressible gas systems with significant pressure drops.
Patm = 14.696 Ć (1 ā 6.8753Ć10ā»ā¶ Ć h)5.2561
where h = elevation in feet
Standards & References
GPSA 14th Edition, Section 17
US Standard Atmosphere 1976 (NASA-TM-X-74335)
AGA Report No. 3 Orifice Metering of Natural Gas
Crane TP-410 Flow of Fluids
Engineering Notes
Two-Thirds Average: Derived from integrating the PĀ² vs flow relationship for compressible gas. Always gives a value slightly higher than arithmetic mean.
When to Use: For pressure drops >10%, the two-thirds method gives more accurate results for Z-factor and density calculations used in flow equations.
Atmospheric Pressure: Decreases ~3.5% per 1,000 ft elevation. Critical for accurate gauge-to-absolute conversion at high elevations.