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What is Diesel Filtration?

Diesel filtration is the method of removing contamination from diesel fuel, by running the fuel through a porous material - or filter - in which contaminates contained in the diesel fuel are retained, whilst the diesel passes through. Contaminates could include dirt particles and water.

The process of filtering oil is also often referred to as oil cleaning or oil cleansing.

Diesel Fuel Filtration Services

FA-ST Ltd offer all types of remedial work to help alleviate and cute these types of problems. We can offer a full package from the sampling and analysis of the fuel, right through the procedures of water removal, waste removal, particulate removal, fuel filtration & polishing to ISO standards, installation of filter units.

We also install pipe work and additional filter systems, transfer pumps & motors, spill prevention and storage units.

Diesel Fuel Cleanliness Guidelines

The overall cleanliness of diesel fuel, or lack thereof, coupled with poor storage and housekeeping practices is the next big problem that all industries in particular transport and power generation will have to deal with. With increasing additions of bio-diesel this also creates additional hazards and responsibilities for storage and house keeping. The fuel cleanliness issues start at the refinery. There the fuel output filtration is typically between 50 and 80 micron. Particles smaller than this are unfiltered and remain in the fuel. The contamination continues when the fuel is taken from the refinery as it may go through several more transfers before reaching the final tanks, boats, tankers, or barrels. These can all contribute to dirt and water ingress.

Much of the problem is related to micron filtration size and water accumulation in diesel fuel as it reaches pumps and injectors. Problems are likely to hit the mobile industry first, as the diesel engine business is the first to deal with EPA's low exhaust emission regulations and with it, the families of new or redesigned engines and especially pump injection systems. Ten years ago, maximum diesel fuel system pressures rarely exceeded 3000 psi, however with today's advanced systems this can be as high as 30,000 psi and therein lies the problem. Most engine fuel filters are nominal 15 or 10 micron and the most damaging particle size by volume is 5-10 microns.

Lab work revealed that particles in the 5 to 10 micron sizes were the most abrasive size group and were the cause of shortened component life. It turned out the 7 micron particle was the perfect fit between micro-machined clearances and would actually grind away or metal surfaces, causing accelerated wear resulting in a drop in pump pressures and causing servo value orifice erosion.

Water ingress to storage tanks is a major problem, particularly for companies who have to store large amounts of fuel for standby, back-up generator systems. Water causes condensation through temperature changes and particularly with older storage tanks contributes to rust that forms within the void between the level of fuel and the tanks. This rusts falls away and causes sediment within the fuel.

Other sources of water ingress are through poorly maintained manhole access points, these can fill with water and seepage can occur through filler caps, breather points and tank lids and faulty seals.

Faulty tanks, cracked pipe work can all contribute to contamination problems within storage tanks.

Fuel Storage Tank Care & Maintenance

Tank cleaning is a major operation which may require complete draining of the tanks, and should only be done by professionals. It is therefore commonly carried out infrequently, normally on the schedule of several years coinciding with (statutory) inspection and maintenance requirements. Good housekeeping can help extend periods between tank cleanings.

Water bottom measurements can be made on an appropriate time interval (via automatic gauging or regular tank dipping with water finding paste) and water can be removed when necessary. This is important since any water and sediment can be stirred up when the tank is filled. After fuel delivers wait 1 hour for every 30cm of fuel to settle and if water and sediment are observed, additional settling time is one way of bringing the fuel back into specification.

It is virtually impossible to stop water from entering the supply chain; therefore, good housekeeping is essential. Hardware, tanks, and pumping systems should be routinely inspected and maintained. Fuel should be checked periodically for contamination by water to ensure there is no free water present in the fuel entering the engine, and dissolved (emulsified) water does not exceed 200ppm.

Diesel Engines Recommendations

This section explains the importance of fuel cleanliness to the successful operation of Cummins® Engines. Modern fuel systems have been developed to reduce emissions and fuel consumption, and improve engine performance. These high pressure systems operate at pressures approaching 2100 bar [30,500 psi] and with component match clearances typically from 2 to 5 microns for injectors. At these pressures, very small, hard particles are potential sources of fuel system malfunction. Excessive contamination of diesel fuel can cause premature clogging of diesel fuel filters and/or premature wear of critical fuel injection system parts. Depending on the size and nature of the particles, this can lead to:

  • Reduced component life

  • Component malfunction

  • Fuel system and/or engine failure

  • Increased exhaust emissions


Determining fuel cleanliness requires measuring both the size and number of particles per size class in the fuel, i.e. the particle size distribution. The International Standards Organization (ISO) has developed a protocol for expressing the level of contamination by coding the size distribution called ISO 4406.

ISO 4406 cleanliness codes are expressed as a series of three numbers (e.g. 18/16/13), which correspond respectively to the number of particles greater than 4, 6, and 14 microns. For example, the numbers in the ISO 4406 rating of 18/16/13 translate to:

  • 18 - Up to 2,500 particles larger than 4μm (per mL of fuel)

  • 16 - Up to 640 particles larger than 6μm (per mL of fuel)

  • 13 - Up to 80 particles larger than 14μm (per mL of fuel)


Engine builders and fuel injection equipment manufacturers have found that the particles greater than 4 microns and greater than 6 microns are particularly critical to the durability of the fuel injection system. They also recognize that the fuel systems must be robust to hard particles smaller than 4 microns that are difficult to filter out, even with the finest filtration. To maximize the efficiency and effectiveness of filtration, Cummins Inc. has adopted the recommendation of the World Wide Fuel Charter that fuel supplied to engines meet the ISO 4406 code of 18/16/13 maximum for respectively 4, 6, and 14 micron particle sizes.

Cummins Inc. recommends that if the fuel does not meet the ISO cleanliness code of 18/16/13 in bulk storage, additional filtration be applied before the fuel is delivered to the equipment's fuel tank.

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