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Parker Engine Mobile OE: Racor Products Blog & Information - North America

Hard and Soft Particle Contamination in Diesel Fuel

Part 3: Revisiting the Racor Filtration Guides

After water, small, hard wear contaminants in small concentrations pose a real threat to engine health. Rust particles and chips from corroding tanks and piping, air blown silica sand and other small particles are common in diesel fuel supply streams. Amazingly, sometimes large identifiable objects such as pebbles, leaves and paint chips can also be found in diesel fuel supplies.

Microscopic hard particles (silica sand) usually make up just a small percentage of the overall contamination present. These particles by themselves usually don’t add much to the clogging of the filter (excluding desert environments), but are potentially devastating to a fuel system. A gram or less of micron-sized silica particles is all that is needed to destroy many high pressure injection systems. In order to guarantee fuel system protection, filter suppliers extensively test engineered medias to meet the high efficiency requirements specified by manufacturers. Media performance of on-engine filters are often specified at 98% or better at stopping particles down to 4 microns size.

Diesel fuel filters are usually plugged by naturally occurring oxidized hydrocarbon chains dissolved in the fuel. These soft particle contaminants stick to each other and to the filter media fibers, building up until they coat and plug the filter. Fuel system heating and fuel aging also contributes to filter plugging by polymerizing the diesel itself into more sticky hydrocarbon chains.

To be effective, fuel filtration devices must meet requirements for hard particle removal efficiency while also resisting clogging by the natural organic contaminants found in diesel fuel.

Notes for future discussion:

  • Next time we’ll cover cold weather operation.

  • A standard filter clogged with organic contaminants will have a hard time removing water from diesel.

  • #1 diesel fuel doesn’t contain soft oxidized hydrocarbon contaminants. So filters used with only #1 diesel fuel plug very slowly.

  • Fuel filter efficiency tests use a special size graded dust as a contaminant.

  • Fuel filter life tests often use an artificial clogging contaminant called SOFTC-2A

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