How does compressing air cause condensation?

Want to know why you end up with condensation in your air compressor? Find out everything you’ll ever need to know in our user-friendly guide.

Estimated time to read: 2 minutes

March 14, 2023

Air, water vapour and condensation

Air usually has a certain level of humidity, meaning it contains a certain amount of moisture, water vapour or condensate. The amount of vapour air is able to absorb depends on the temperature of the air. The higher the temperature of the air, the more water vapour it absorbs or holds.

The maximum amount at any given temperature is called the relative humidity. When relative humidity reaches 100%, the air is no longer able to absorb any more water vapour. This is known as a saturation point or a dew point. It’s the point at which condensation begins to form. 

Compressed air and condensation

The higher the temperature of air going into an air compressor, the more water vapour in the air and, as such, the more condensation that will be produced. If the ambient air temperature is 20°C, there will be about 17.30 g/m3 of moisture in the air. At 35°C, this more than doubles to 39.63 g/m3.

When the air is compressed the temperature initially rises, even as the volume of air – what we just saw as m3 – reduces.

The air will also eventually cool. And as it cools, the amount of moisture in the air won’t change. Instead, because the compressed air has less volume, it will be unable to hold as much water vapour or condensate, resulting in condensation. 

How much condensation depends on the temperature and pressure of the compressed air. At a pressure of 800 kPa, the compressed air has only 1/8 the volume it previously had. This means it will only be able to hold 1/8 of the condensate. The rest turns into condensation as soon as temperatures begin to drop.

This means condensation needs to be removed from compressed air before the temperature drops, which usually happens when the air is discharged from the air compressor. For this reason, a condensation or adsorption dryer is used to eliminate condensation.

Avoiding condensation in compressed air

What else will help to reduce condensation? Keep the temperature of your intake air as low as possible. This is particularly important in the summer months, or if you’re working in a particularly warm or humid environment. 

Would you like to know more about air dryers? Take a look at our guide. Do you have a question about condensation in compressed air? Or anything else do with air compressors? The experts at ALUP are at your service.

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