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Technical Reference

FAQs - Fuel Filtration

Q: What is the meaning of efficiency in Q: What is the difference between a primary
relation to a fuel filter? and secondary diesel fuel filter?
Efficiency is the ability of the filter to remove particulate (% The primary fuel filter must offer low restriction because
efficient) at a given micron (size). The type of media being it is mounted on the suction side of the fuel pump where
used ultimately defines the filter’s efficiency. 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
Q: What is the capacity of a fuel filter and fuel filter (if installed). Primary fuel filters typically have a
how is it measured? nominal rating of 10 - 30 microns.

Capacity is the measurement (in grams) of the total amount Secondary fuel filters are mounted between the transfer
of containment a filter can retain at a rated flow and pump and the injectors. The secondary fuel filter is designed
given end-point (restriction). The type of media (i.e. glass, to offer full protection to the fuel injectors. Since these
cellulose, synthetic, etc.) and the amount (square inches) of filters are mounted after the transfer pump they tend to see
media defines capacity. much higher pressures than primary filters. Secondary fuel
filters typically have a nominal rating of 2 - 10 microns.
Q: What is restriction?
Restriction is the pressure drop across the filter at a given Q: What is the purpose a fuel/water
flow, temperature, and fluid viscosity. The type of media and separator?
general filter construction defines restriction.
Water flowing at high velocity between highly polished
valve seats and through fine nozzle orifices causes a
Q: What is hydrostatic burst pressure? wearing action that approaches that of abrasion. The
presence of water, especially with entrained air and various
ENGINE LIQUID FILTRATION TECHNICAL REFERENCE
The hydrostatic burst pressure of a filter is its ability to fuel components, causes rust and other chemical corrosion
withstand a deadhead pressure and is typically measured that eats away at the finely mated surfaces. Fuel/water
in pounds per square inch. The type of lock-seam, material separator filters use chemically treated paper to repel water
thickness (bottom and body of filter), shape of tapping plate, which then settles by gravity to the bottom of the filter.
and gasket contribute to hydro performance. Accumulated water can be drained from the filter during
recommended service intervals if equipped with a drain
valve or plug.
Q: How often should system maintenance be
performed?
Q: What is asphaltene?
This is totally dependent on the type of SCA you have
chosen to use. Refer to engine and additive manufacturer All diesel fuels to a degree contain a substance known as
recommendations. 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
Q: How can I estimate my engines total fuel system, as they are soft and deformable. As these tiny
flow rate? particles pass through the filter media they tend to stick to
the individual fibers. If you were to cut open a filter that
If this information is not available from your engine or had choked after a normal service interval you would see
equipment manufacturer, use the following formulas for a black, tarry substance on the dirty side of the filter; this is
estimating purposes. asphaltene (oxidized fuel).

Diesel or kerosene fuel systems:
Gallons per Hour is Engine Horsepower (maximum) Q: What is a micron?
multiplied by 18% or GPH = HP X 0.18
The common unit of measurement in the filtration industry
is the micron or micrometer. One micron equals forty
Gasoline fuel systems (carbureted): millionths of an inch (.00004). In comparison, a human hair
Gallons per Hour is Engine Horsepower (maximum) is approximately 70 micrometers. Reference FMC TSB-89-5R2
multiplied by 10% or
GPH = HP X 0.1
Q: How often should I change my fuel
Gasoline fuel systems (fuel injected):
Use a straight 40 GPH figure. filter(s)?
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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