Engineering ToolBox - Resources, Tools and Basic Information for Engineering and Design of Technical Applications!

Compressed Air vs. Free Air - Compression Ratio

The ratio of compressed air pressure to free air pressure.

Sponsored Links

Free air is air at ambient conditions at a specific location where 

  • ambient temperature
  • moisture content
  • barometric pressure

are stated.  

Compression Ratio

Compression Ratio is based on the Ideal Gas Law and is the ratio between Discharge Pressure Absolute and Suction Pressure Absolute.

CR = pd / ps                                (1)

where

CR = compression ratio

pd = discharge absolute pressure (bar abs, psia)

ps  = suction absolute pressure (bar abs, psia)

The compression ratio of free air - to compressed air, is indicated in the diagram below.

Compression Ratio - Pressure (psi)

Compression ratio - pressure of compressed air to pressure of free suction air diagram - psi

  • 1 psi = 6.9 kPa = 0.069 bar
  • 1 ncfm = 0.5 nl/s

Converting Compressed Air Volume Flow to Free Air Volume Flow

A compressed air volume flow can be converted to a free air volume flow by using the equation

qF = CR qC                            (2)

where

qF = free air flow (m3/s, cfm)

qC = compressed air flow (m3/s, cfm)

Example - Converting Compressed Air Volume Flow to Free Air Volume Flow

A compressed air volume flow of 10 acfm (actual cfm) at 100 psig must be multiplied with Compression Ratio approximately 8 to estimate the volume of free air at atmospheric pressure.

qF = 8 (10 acfm) 

    = 80 scfm  (standard cfm)

Compression Ratio - Pressure (bar)

Compression ratio - pressure of compressed air to pressure of free suction air diagram - bar

Example - Converting Free Air Volume Flow to Compressed Air Volume Flow

A free air volume flow of 1 m3/s is compressed to 10 bar (gauge) and must be divided with Compression Ratio approximately 11 to estimate the volume of compressed air.

qC = (1 m3/s) / 11

             = 0.091 m3/s

Sponsored Links

Related Topics

Related Documents

Sponsored Links

Engineering ToolBox - SketchUp Extension - Online 3D modeling!

3D Engineering ToolBox Extension to SketchUp - add parametric components to your SketchUp model

Add standard and customized parametric components - like flange beams, lumbers, piping, stairs and more - to your Sketchup model with the Engineering ToolBox - SketchUp Extension - enabled for use with the amazing, fun and free SketchUp Make and SketchUp Pro .Add the Engineering ToolBox extension to your SketchUp from the SketchUp Pro Sketchup Extension Warehouse!

Translate
About the Engineering ToolBox!

Privacy

We don't collect information from our users. Only emails and answers are saved in our archive. Cookies are only used in the browser to improve user experience.

Some of our calculators and applications let you save application data to your local computer. These applications will - due to browser restrictions - send data between your browser and our server. We don't save this data.

Google use cookies for serving our ads and handling visitor statistics. Please read Google Privacy & Terms for more information about how you can control adserving and the information collected.

AddThis use cookies for handling links to social media. Please read AddThis Privacy for more information.

Citation

This page can be cited as

  • Engineering ToolBox, (2008). Compressed Air vs. Free Air - Compression Ratio. [online] Available at: https://www.engineeringtoolbox.com/free-compressed-air-d_1190.html [Accessed Day Mo. Year].

Modify access date.

. .

close

3D Engineering ToolBox - draw and model technical applications! 2D Engineering ToolBox - create and share online diagram drawing templates! Engineering ToolBox Apps - mobile online and offline engineering applications!

Scientific Online Calculator

Scientific Calculator

3 10

Sponsored Links
.