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FAQ: DIESEL FUEL FILTRATION

Posted: August 1, 2014

What is the meaning of efficiency in relation to a diesel fuel filter?
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.

What is the capacity of a diesel fuel filter and how is it measured?
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 endpoint (restriction), fluid flow rate, filtering area, and the type of filter medium tested.

What is restriction?
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.

What is hydrostatic burst pressure?
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.

How can I estimate my engines total fuel flow rate?
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

What is the difference between a primary and secondary diesel fuel filter?
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.

What are asphaltenes?
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.

What is the purpose of a diesel fuel/water separator?
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.

What is a micron?
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.

How often should I change my diesel fuel filter(s)?
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.

What is the “cloud point” of diesel fuel and why is it important to filtration?
#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.

Should I use diesel fuel additives?
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.

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