Compressed air traps should be installed on the inter coolers to automatically drain the condensed water and ensure smooth system operation.
When air is compressed, as per laws of thermodynamics, there is a corresponding rise in its temperature. An intercooler, fitted between the stages of a multi-stage compressor, is used to cool the compressed air which has been heated due to compression. The compressed air is cooled because it makes the air denser and thus the subsequent stages of the compressor use less power for a given CFM output. Additionally this also prevents the air reaching temperatures which can lead to explosion due to the lubricating oil in it.
Atmospheric air always contains a proportion of water vapor. How high this proportion is will depend on the relative humidity in atmosphere. Under most conditions, the air leaving the compressor will just be able to carry its initial moisture content. Subsequently, any cooling which takes place will cause the air to shed its excess water vapor by condensing. This water vapor if allowed to pass to the next compression stage could condense on the cylinder walls resulting into damage to the compressor.
It is essential that this condensed water is drained away from the inter cooler and this can best be done automatically using a compressed air trap. Though manually draining the intercooler also works, however only if it is drained regularly by the operator. However, this is rarely the case. Thus to ensure the compressor operates smoothly an automatic drain trap should be installed at the intercooler.