Filter Manufacturers Council – Heavy Duty Diesel Fuel Filters

Heavy Duty Diesel Fuel Filters

Frequently Asked Questions

Q: What is the meaning of efficiency in relation to a fuel filter?
A: Efficiency is the ability of the filter to remove particulate (% efficient) at a given micron (size). The type of media being used ultimately defines the filter’s efficiency.

Q: What is the capacity of a fuel filter and how is it measured?
A: Capacity is the measurement (in grams) of the total amount of containment a filter can retain at a rated flow and given end-point (restriction). The type of media (i.e. glass, cellulose, synthetic, etc.) and the amount (square inches) of media defines capacity.

Q: What is restriction?
A: Restriction is the pressure drop across the element at a given flow, temperature, and fluid viscosity. The type of media and general filter construction defines restriction.

Q: What is hydrostatic burst pressure?
A: The hydrostatic burst pressure of a filter is its ability to withstand a deadhead pressure and is typically measured in pounds per square inch. The type of lock-seam, material thickness (bottom and body of filter), shape of tapping plate, and gasket contribute to hydro performance.

Q: How often should system maintenance be performed?
A: This is totally dependent on the type of SCA you have chosen to use. Refer to engine and additive manufacturer recommendations.

Q: How can I estimate my engines total fuel flow rate?
A: If this information is not available from your engine or equipment manufacturer, use the following formulas for estimating purposes.

Diesel or kerosene fuel systems:
Gallons per Hour is Engine Horsepower (maximum) multiplied by 18% or GPH = HP X 0.18

Gasoline fuel systems (carbureted):
Gallons per Hour is Engine Horsepower (maximum) multiplied by 10% or
GPH = HP X 0.1
Gasoline fuel systems (fuel injected):

Use a straight 40 GPH figure.

Q: What is the difference between a primary and secondary diesel fuel filter?
A: The primary fuel filter must offer low restriction because it is mounted on the suction side of the fuel pump where normally a suction pressure of only 5-6 pounds per square inch is available. This filter has the job of protecting the transfer pump and lightening the load of the secondary fuel filter (if installed). Primary fuel filters typically have a nominal rating of 10 – 30 microns.

Secondary fuel filters are mounted between the transfer pump and the injectors. The secondary fuel filter is designed to offer full protection to the fuel injectors. Since these filters are mounted after the transfer pump they tend to see much higher pressures than primary filters. Secondary fuel filters typically have a nominal rating of 2 – 10 microns.

Q: What is the purpose a fuel/water separator?
A: Water flowing at high velocity between highly polished valve seats and through fine nozzle orifices causes a wearing action that approaches that of abrasion. The presence of water, especially with entrained air and various fuel components, causes rust and other chemical corrosion that eats away at the finely mated surfaces. Fuel/water separator filters use chemically treated paper to repel water which then settles by gravity to the bottom of the filter. Accumulated water can be drained from the filter during recommended service intervals if equipped with a drain valve or plug.

Q: What is asphaltene?
A: All diesel fuels to a degree contain a substance known as asphaltene. Asphaltene is a by-product of fuel as it oxidizes. Asphaltene particles are generally thought to be in the half micron – 2-micron range and are harmless to the injection system, as they are soft and deformable. As these tiny particles pass through the filter media they tend to stick to the individual fibers. If you were to cut open a filter that had choked after a normal service interval you would see a black, tarry substance on the dirty side of the element; this is asphaltene (oxidized fuel).

Q: What is a micron?
A: The common unit of measurement in the filtration industry is the micron or micrometer. One micron equals forty millionths of an inch (.00004). In comparison, a human hair is approximately 70 micrometers.
Reference FMC TSB-89-5R2

Q: How often should I change my fuel filter(s)?
A: Always follow the equipment or engine manufacturers recommendation on change intervals. The type of equipment and its usage will determine how often the filters need to be changed.

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