Understanding Inner Air Elements
In a single day of driving, an engine can consume more than one million gallons of air — air that contains suspended dirt and dust. Without proper filtering to remove these contaminants, an engine could be ruined in as few as 500 miles (800 km). Some engine air applications require two air filters – an outer and an inner element.
The outer or primary filter element is designed to remove contaminants from the air coming into the intake system. This is the workhorse of the air intake filtration system.
The inner or secondary air filter element generally fits inside the larger outer element. The inner element is sometimes referred to as a safety element.
The inner element provides protection from contaminants that may enter the air intake system when the outer element is removed as part of scheduled service.
Due to size limitations of the inner element, a much smaller amount of filter media is contained in the element. The element typically utilizes media that is more open than that of the primary filter. To allow the same amount of air to flow as the outer element, the media in the inner element is less efficient at contaminant removal than the outer element.
The inner element should be changed approximately every third outer element change interval. The inner element should never be used without the outer element to prevent major engine damage.