Air velocities in vacuum pipes can be estimated with the diagrams below.
Standard and Actual Air Volume - cfm
The diagram is calculated for steel pipes schedule 40.
Example - Estimating the Vacuum Air Flow Velocity
Velocity in a NPS 3" steel pipe with standard air volume flow 100 scfm at 30% vacuum can be estimated to approximately 3000 fpm as indicated in the diagram below:
Standard and Actual Air Volume - l/s
Air, LNG, LPG and other common gas properties, pipeline capacities, sizing of relief valves.
Vacuum is defined as air pressure below atmospheric pressure.
Convert vacuum air volume to standard air volume
Vacuum pumps - calculate flow rate and required evacuation time.
Measure air volume flow in vacuum.
Converting between vacuum units like % vacuum - mm Mercury - psi - torr - micron - kPa.
Calculate pressure drops in vacuum pipe lines.
Online calculator, figures and tables giving the boiling temperatures of water in varying vacuum, SI and Imperial units.