Large heavy duty equipment engines typically uses two air filters as part of its air intake filtration system. Understanding this system will lead to a more efficient engine, less preventive or corrective maintenance, and better engine performance.

The air intake system: Normal air that we breathe contains impurities, both large and microscopic. In an industrial environment where there are movement of materials and machines, the levels of airborne particles that are present can be many times more than a non-industrial environment. There are many airborne pollutants present; however the most important are the airborne Particulate Matter (PM). This is the term used for a type of air pollution that consists of varying mixtures of particles suspended in the air. Examples of Particulate matter are dirt, soil dust, pollens, molds, ashes, sand, gravel dust, stone dust, soot and aerosols that are formed in the atmosphere from gaseous combustion by-products such as volatile organic compounds, sulfur dioxide, and nitrogen oxides. Particulate matter is directly emitted into the air by sources such as factories, power plants, vehicles, construction, fires and natural windblown dust.

This air is combined with hydrocarbons in the form of gasoline, diesel, or liquid petroleum gas that is burned in an enclosed area, producing power that moves engine components to provide torque and movement.

Usually, when the engine is first cranked, a partial vacuum develops in the engine cylinders above the piston heads. This partial vacuum pulls in air via an outer air filter, then through an inner air filter, sometimes through an oil bath, through an intake manifold, to the engine cylinders where it mixes with fuel to produce combustion. This air passage sometimes includes turbochargers and preheaters.

The impurities in the air, most notably the stone, sand, and gravel dust, are highly abrasive to the internal engine components. If this abrasive particulate matter is allowed to be pulled into the engine, it will be lodged in the turbocharger bearings, and between the pistons and the cylinder liners. This wears out the turbocharger, and damages the pistons, rings, and liners leading to increased lubricating oil consumption.

The Outer Air Filter stops the larger particulates and other objects in the air stream at the time of operation. This is considered the initial stage of air filtration; however, the smaller abrasive sand, gravel, stone, and dust particulates will all pass this initial outer air filter. It’s worth remembering that this outer air filter only stops large particulate matter that is typically visible to the naked eye. The small particulate matter that is virtually invisible to the naked eye passes through to the inner air filter.

The Inner Air Filter is tasked with the removal of the most dangerous particulate matter that can drastically reduce an engine’s lifespan if not used. This filter may have been designed to meet SAE HS806, J726 and J906 standardized tests to ensure that a large percentage of the abrasive particulates are filtered, and only clean air is fed into the engine.

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