An air dryer may be installed in the compressor discharge line between the compressor and the first reservoir. Its purpose is to remove water vapour and contaminants from compressor air before the air enters the first reservoir. The first reservoir has usually been the supply or “wet” reservoir, so called because moisture accumulated in that reservoir before the air flowed from there to the service reservoirs. However, today’s air dryer technology is so effective that a “wet” reservoir may not be needed anymore. In a modern Air Dryer Integrated System (ADIS), the air compressor governor and the air dryer are combined into a single unit. Air from the air dryer goes directly into the primary and secondary service (“dry”) reservoirs