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Technical
Service Bulletin 95-1R1
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Diesel Fuel Contamination and Fuel Filter Plugging
Fuel
contamination is a fact of life. Preventing problems and equipment damage
associated with contaminated fuel is primarily the responsibility of the
end user. These responsibilities include the proper and timely replacement
and servicing of the filters; selection of the fuel source, grade, and
blend; and use of heaters, separators, and additives as required.
Fuel
filters capture unwanted contaminants from the fuel. Left unchecked, these
contaminants may cause serious and expensive damage to many system components
including pumps, lines, and injectors. Fuel contaminants have many sources.
Most sources are external to the fuel system itself, that is, most contaminants
come with the fuel that is delivered to the fuel tank. As it comes from
the refinery, diesel fuel is clean. Contaminants in diesel fuel are generally
introduced in fuel storage systems through mixing, transferring, and storage.
Fuel
filters naturally build resistance to the flow of fuel as they go about
their job of removing unwanted contaminants from the fuel system. Fuel
systems, unlike lube systems, do not have the opportunity for bypass flow
and consequently, as flow through the fuel filter decreases, decreased
performance of the fuel system and the engine will result. Fuel filters
will become restricted or plugged over their life -- this is an expected
result. A thorough investigation of the filter and the fuel source should
be conducted anytime a fuel filter is suspected of delivering less than
its expected life.
Some
common contaminants found in today's fuels might include:
Water
-- is the greatest concern because it is the most common form of contaminant.
Water may be introduced into the fuel supply during fueling when warm,
moisture laden air condenses on the cold metal walls of fuel storage tanks
or from poor housekeeping practices. The effects of water in diesel fuel
can be serious. Water can cause a tip to blow off an injector, or reduce
the lubricity of the fuel which can cause seizure of close tolerance assemblies
such as plungers.
Once
in the system, water can be removed by using in-line water separating
filters or devices. Long term prevention of problems associated with water
in fuel is best accomplished by obtaining fuel from reputable suppliers
capable of providing high quality fuel. Further, fuel tanks should be
kept well filled to prevent condensation, and fuel should be drawn from
the top of a storage tank if possible, as water is heavier than diesel
fuel and tends to settle to the bottom of storage tanks. Tanks can also
be kept free of water with continuous off-line or "kidney-loop"
filtration/separation.
Fungus
and Bacteria -- These micro-organisms live in water and feed on the
hydrocarbons found in fuel. Called Humbugs for short, these active and
multiplying colonies will spread throughout a fuel system and quickly
plug a fuel filter. The fuel filter will have a slime coating over the
surface of the media, dramatically reducing the service life of the filter.
Bacteria may be any color, but is usually black, green or brown. Draining
the system will reduce microbial activity, but will not eliminate it.
The only way to eliminate microbial growth once it has started is to clean
and treat the system with a biocide.
Wax
-- while desirable as a source of energy in fuel, control in cold
weather operation is needed. Wax crystals form as a result of cold temperature
precipitation of paraffin. Temperatures below a fuel's cloud point will
result in wax precipitation and filter plugging. To prevent plugged filters
due to wax formation, the cloud point of fuel must be at least 12°
Celsius (+22°F) below the lowest outside temperature. Fuel suppliers
blend diesel fuel based on local anticipated cold weather conditions.
Particular attention should be given to diesel fuel purchased outside
your local area. For example, fuel purchased in the West or South may
not be suitable for operating conditions in the Midwest or North.
Asphaltines
-- are components of asphalt that are generally insoluble and are
generally present to some extent in all diesel fuel. These black, tarry
asphaltines are hard and brittle, and are made up of long molecules. Fuel
with a high percentage of asphaltines will drastically shorten the life
of a fuel filter.
Sediment
and other solids -- often get into fuel tanks and cause problems.
Most sediment can be removed by settling or filtration. Fuel filters designed
for specific applications will remove these harmful contaminants before
they cause further system wear and damage.
In
no case should a more "open" filter be substituted to fix a
perceived problem with premature plugging. Plugged filters will develop
as the filter works to remove unwanted contaminants from the fuel system.
Filter manufacturers design fuel filters to provide the level of filtration
protection specified or required by the OEM manufacturer. Substitution
of a more "open" filter may prolong a filter's life before plugging
occurs, but it will also allow unwanted contaminants to pass downstream
which will eventually impact the life of other, more expensive fuel system
components.
Clean
fuel is essential for efficient, full-power engine performance. Remember,
newly refined fuel is clean. Between the time the fuel leaves the refinery
and enters the engine's fuel tanks, it should be handled carefully to
avoid possible contamination that can prematurely plug fuel filters and
cause even further, more serious damage within the engine's fuel system.
For additional information, contact:
Filter Manufacturers
Council
P.O. Box 13966
Research Triangle Park, NC 27709-3966
Phone: 919/406-8817 Fax: 919/406-1306
www.filtercouncil.org
Administered by Motor & Equipment
Manufacturers Association
Revised October 2002
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