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How to Test Your AirPrep AfterCooler to Ensure It’s Working

Besides nozzle pressure, the second most important aspect of your compressed air is its temperature. All blasters should strive for cool, dry air. Using an air prep/cooling system helps ensure you’re removing moisture from the blast air coming in direct contact with the steel surface.

However, many contractors are unfamiliar with how to check to ensure their air preps are working properly. The easiest way is to measure what is referred to as the Approach Temperature.

Approach temperature is the difference between the compressed air exiting the air prep radiator (the outlet temperature)… and the ambient temperature (the general environment temperature).


Compressed air is very hot – generally around 90°C (200°F) as it enters the radiator. A properly sized radiator will cool this to within 10-12 degrees Celsius (or 15-20 degrees Fahrenheit) of the ambient temperature. For example, let’s pretend the ambient temperature is a mild 20°C (70°F)– so your air prep should be able to cool the compressed air to within 32°C (90°F). Approach temperatures greater than 12°C (20°F) will compromise the efficiency and quality of your blast.

Using the DeFelsko DPML (Dew Point Meter Logger) is an easy way to measure your ambient and outlet temperatures to determine the Approach Temperature of your system. Again, any Approach Temperatures greater than 12°C (20°F) indicates you’re radiator is not large enough to cool your air flow.

Other Issues Possibly Causing High Approach Temperatures (in addition to the undersized radiator)

  • Insufficient air pressure to the fan motor – refer to the manual to establish the correct pressure.
  • Blocked radiator – these need to be regularly cleaned with a pressure washer to remove dust and debris.
  • Worn out fan or air motor – giving poor performance.
  • Air motor running backwards – only moves +/- 50% of the required airflow.
  • Blocked air motor discharge silencer – if the air can’t get out of the silencer the motor cannot generate power.

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