How Compressed Air is Made: The Whole Journey

Let's take a look at a compressed air system and see what happens when we create, store, transport and use compressed air.

We can divide a compressed air system into different blocks, each with their own distinct role: production (the air compressors), treatment (filters and dryers), storage (the air receiver), distribution (the piping system) and usage (the compressed air users).

Below, we follow the air through all of them: from the ambient air around us to the tool that does the work. Every step links to the page that covers it in detail.

1. Air is sucked in

   Air is sucked in through the air inlet filter. The inlet filter makes sure that all the dust and dirt stays outside. It's also the first step in making sure that the compressed air is clean: all the dust that is sucked in will eventually end up in the compressed air!

   Compressor air filtersPart page
2. Past the inlet valve

   Before the air enters the screw element, it passes the inlet valve. This valve opens and closes the air supply to the screw element. When it's open, the compressor is running 'loaded': actually compressing air and pumping it into the system. When it's closed, the compressor runs 'unloaded'.

   Air compressor inlet valvePart page Unloader valvePart page
3. Compression and oil injection

   The screw element works like a pump and compresses the air. During this process, oil is injected in the element. The oil is there to cool the air (the air gets very hot during compression), for lubrication, and for sealing the clearances between the screws. Now we have a mixture of compressed air and compressor oil.

   Rotary screw compressorsCompressor type Screw element (air-end)Part page
4. Separating the oil from the air

   Now we need to separate the oil and the air again. Most of the oil is separated from the compressed air by centrifugal force (just like what happens in a clothes tumble dryer). The remaining oil, mostly small droplets and oil mist, is separated by the separator element. The oil stays in the compressor; the compressed air moves on.

   How a screw compressor worksOil separation explained Air compressor oilPart page
5. Cooling down, and the first water

   The compressed air is still very hot at this point, about 80 degrees Celsius. The after cooler cools it down to around 25–40 degrees before it leaves the compressor. Because of the cooling down, a lot of water vapor condenses into liquid water, which is removed by the condensate trap. The compressed air now finally leaves the compressor.

   Compressed air contaminantsAir quality
6. Treatment: drying and filtering

   The compressed air still contains too many impurities (dust, water, oil) to be used directly. So it is treated with the help of compressed air dryers and compressed air filters. Typically, a refrigerated compressed air dryer lowers the air temperature to about 4 degrees Celsius, to let most of the remaining water condense into liquid.

   Compressed air dryersAir quality Compressed air filtersAir quality
7. Storage

   After treatment, the clean compressed air is typically stored in a big air receiver. Storage stabilizes the system: more storage makes the system more stable: the pressure rises slower, but it also drops slower in case of a demand spike.

   Air receiversSystems
8. Distribution

   From the air receiver, the compressed air flows through a piping system to the compressed air users. Along the way it loses some pressure: pressure drop, the difference in pressure between two points, the result of the compressed air flow hitting obstructions on its way.

   Compressed air pipingSystems Pressure dropBasics
9. The air does its work

   Finally, we use the compressed air in a machine or tool. The machine does some work for us, and the compressed air expands back to the volume it was before.

   Air compressor usesOverview