Fuel Filter Information

Fuel Filter Information

Postby Jimbo » Wed Apr 09, 2008 7:55 pm

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.

Diesel Paraffin (Wax) Choking
All diesel fuel contains wax. As the temperature of diesel fuel is reduced, wax crystals begin to settle out of solution. This temperature is known as the cloud point, the temperature at which the fuel goes from a clear appearance to a cloudy appearance. The fuel filter begins to choke as more and more wax crystals begin settling out of solution and moving through the fuel system. A yellow, waxy substance eventually envelopes the filter and prevents the passage of fuel.



There are normally several fuel filters found within a diesel fuel system. These filters must prevent tiny particles from reaching the engine and are susceptible to failure from asphaltene and wax. E-ZOIL manufactures several cold flow improvers that will keep wax crystals in solution to prevent fuel filter plugging. These products include DIESEL AID, ARTIC POWER, and ARTIC FLO. These three products will depress the pour point and cold filter plugging point of diesel fuel and provide other benefits

Proper filtration of diesel fuel is critical to maintaining the performance and long life of a diesel engine. In order to produce and control the extremely high injection pressures common in a diesel, the injection pump components and nozzles are machined to extremely close tolerances - often measured in microns (one micron is 40 millionths of an inch). To prevent the premature failure of these vital components, it is critical that diesel fuel be filtered to remove extremely small particles of foreign matter. The particles that a secondary or final fuel filter, for example, are in the range of 5-10 microns (.0002 - .0004"). To illustrate how small these tolerances are, consider that:
• The naked eye cannot see particles smaller than 40 microns.
• A grain of sand is approximately 100 microns.
• A human hair is approximately 70 microns.
• A single grain of talcum powder is 10 microns.

The greatest enemy of diesel fuel injection components is water. Once water enters the fuel system, it will rapidly wear and oxidize steel components and lead to:
• Rusting and corrosion of components
• Governor/metering component failure
• Sticky metering components (both pump and nozzle)
• Injection component wear and seizure

Water contamination can exist in diesel fuel in three forms:
1) Emulsified water, where the water is suspended in the fuel like oil and vinegar in salad dressing.

2) Free water, where the water is separated from the fuel and usually is found on the bottom of fuel/storage tanks.

3) Dissolved water, where the water has been chemically dissolved in the fuel, like sugar in coffee. The warmer the fuel, the more water will be dissolved, but as temperatures drop, the water will come out of the solution in the form of free water.



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