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# Vacuum - Air Expansion Ratio

## Convert vacuum air volume to standard air volume

Standard air volume flow - SCFM - can be converted to actual air volume flow - ACFM - with the expanded air ratio equation

EAR = (30 / P) ((T + 460) / 520)                                            (1)

where

EAR = ACFM / SCFM = expanded air ratio - ratio between actual air volume flow - ACFM - and standard air volume flow - SCFM

P = absolute vacuum pressure (inches Hg) where 29.92 inches Hg is normal atmospheric pressure and 0 inches Hg is absolute vacuum

T = temperature (oF)

Actual air volume flow can be calculated by multiplying standard air volume with the expanded air ratio.

Expanded air ratio for temperatures 60oF (15.5oC) are indicated in the diagram below:

The diagram above can be used to calculate air flow in SI-units where

• actual air flow - al/s
• standard air flow - sl/s

#### Example -  Vacuum Expansion of Air

From the table above the expansion ratio of air from atmospheric pressure to 50% vacuum is 2

The relation between vacuum in % and other pressure units are indicated in

## Related Topics

• ### Gases and Compressed Air

Properties of air, LNG, LPG and other common gases. Pipeline capacities and sizing of relief valves.

## Related Documents

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Vacuum is defined as air pressure below atmospheric pressure.
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Measure air volume flow in vacuum.
• ### Vacuum - Pressure Units Converter

Converting between vacuum units like % vacuum - mm Mercury - psi - torr - micron - kPa.
• ### Vacuum Pipes - Flow Velocities

Air velocity diagrams for vacuum pipe lines.
• ### Vacuum Pipes - Pressure Loss vs. Air Flow

Calculate pressure drops in vacuum pipe lines.
• ### Water - Boiling Points at Vacuum Pressure

Online calculator, figures and tables giving the boiling temperatures of water in varying vacuum, SI and Imperial units.

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## Citation

• The Engineering ToolBox (2008). Vacuum - Air Expansion Ratio. [online] Available at: https://www.engineeringtoolbox.com/vacuum-expanded-air-ratio-d_1194.html [Accessed Day Month Year].

Modify the access date according your visit.

6.3.17

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