Frequently Asked Questions
Heavy Duty - Diesel Fuel Filtration
Q: What is the meaning of efficiency in relation to a diesel fuel filter?
A:
Efficiency is the laboratory test measure of the
ability of a filter to trap calibrated particulate dispersed in a specified
fluid, under specified test conditions. Efficiency is best expressed
as a percent of calibrated particulate removed equal to or larger than,
a given micron size. Example: 98% @ =5 microns.
Reference FMC TSB-89-5R2
Q: What is the capacity of a diesel fuel filter and how is it measured?
A:
Capacity is the laboratory test measure (in grams) of the ability of
a filter to resist clogging under specified test conditions. Tests generally
involve addition of a contaminant slurry into a laboratory flow system
so that the time that the filter survives the test can be directly calculated
into a grams capacity. Capacity is dependant on the test end?point (restriction),
fluid flow rate, filtering area, and the type of filter medium tested.
Reference FMC TSB-95-1R1
Q: What is restriction?
A:
Restriction is the pressure drop across the filter at a given flow,
temperature, and fluid viscosity. The type of media and general filter
construction defines restriction. Increased restriction from fuel contaminants
(usually asphaltenes) limits fuel flow and causes loss of power.
Reference FMC TSB-95-1R1
Q: What is hydrostatic burst pressure?
A: The hydrostatic burst pressure of a filter is its ability to withstand a deadhead fluid pressure and is typically measured in pounds per square inch. The type of lock-seam, material thickness (bottom and body of filter), shape of tapped plate, and gasket contribute to hydrostatic burst performance.
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
Q: What is the difference between a primary and secondary diesel fuel filter?
A: A primary diesel fuel filter is the first filter in a two filter system. It is located before the secondary filter, and usually before any transfer pump in the system. A primary filter is used to remove the bulk of free water and contaminants and thus protect the transfer pump (if present) and secondary filter. Typical primary filter efficiency is 95% to 98% @ =10 to 50 microns.
A secondary filter is the second filter in a two filter system. It is located between the primary filter and the fuel injection system, often after a transfer pump. Typical secondary filter efficiency is 95% to 98% @ = 3 to 10 microns. Newer high pressure fuel injection systems require removal of the smallest measurable hard particles.
The main
advantage of a two filter system over a single filter system is that
much of the dissolved asphaltenes present in diesel fuel are caught
by the primary filter, leaving the secondary filter relatively clean
and ready to remove free water and fine particles. A properly sized
two filter system will often outlast and outperform a similarly rated
single fuel filter system.
Reference FMC TSB-89-5R2
Q: What are asphaltenes?
A: Asphaltenes
are tarry, organic particles that naturally occur in #2 diesel fuels.
Asphaltene particles are generally thought to be in the one-half to
2 micron range and are harmless to the injection system, as they are
soft and deformable. Concentrations of asphaltenes in diesel fuel vary
widely and can increase through heat and fuel oxidation. As these tiny
particles pass through the filter media they tend to stick to individual
fibers. A build up of asphaltenes is the normal mechanism that plugs
diesel fuel filters, not hard particles.
Reference FMC TSB-95-1R1
Q: What is the purpose of a diesel fuel/water separator?
A: Diesel
fuel has a background "humidity" of water that cannot be removed.
Water that exists freely as an emulsion or as droplets, is a concern
for fuel system components. Free 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 free
water, especially with entrained air and various fuel components, causes
corrosion of the finely mated surfaces. Fuel/water separator filters
use chemically treated filter media 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. Note that alcohol based diesel fuel additives
may severely degrade fuel/water separator performance.
Reference FMC TSB-91-1R2 and
TSB-95-1R1
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 microns.
Reference FMC TSB-89-5R2
for further details
Q: How often should I change my diesel fuel filter(s)?
A:
Always follow the equipment or engine manufacturer's recommendation
on change intervals. However, frequency of filter replacement is often
determined by the level of contaminants in the fuel. Combinations of
high asphaltene concentration, water, sludge, bacterial growth, etc.,
in diesel fuel can prematurely plug a fuel filter and render a fuel/water
separator ineffective. Filter change intervals should be based on knowledge
of the fuel quality being filtered.
Reference FMC TSB-95-1R1
Q: What is the "cloud point" of diesel fuel and why is it important to filtration?
A: #2 diesel fuel has a wax component that contributes to the lubricity and heat value of the fuel. The "cloud point" refers to the temperature when the wax precipitates out of the fuel in the form of small wax crystals. Different fuel blends can have very different cloud point temperatures, generally ranging from -10°F to +40°F. #1 diesel fuel does not contain large amounts of wax, and therefore does not have a noticeable cloud point. Diesel fuel distributors blend local diesel fuel supplies so that the cloud point is usually not reached. However, if ambient temperatures fall below the cloud point of the fuel on a vehicle, the precipitated wax crystals can quickly coat and plug a filter element.
To avoid
filter wax plugging and loss of engine power, diesel fuel filter systems
are often supplied with an auxiliary fuel heating or return fuel heat
recovery systems. Fuel additives are also available that modify the
formation of wax crystals, making them less likely to plug the filter.
Reference FMC TSB-91-1R2
Q: Should I use diesel fuel additives?
A: Always follow the equipment or engine manufacturers' recommendations for the use of fuel additives. Note that alcohol based additives will degrade fuel/water separator performance.