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By Capt. Jeff Werner
Water is the most damaging contaminant found in diesel fuel. Growth of bacteria, mold, yeast or other types of fungi in a diesel fuel tank cannot occur without the presence of water.
Water gets mixed with fuel in a variety of ways. Freshly refined diesel contains some water, and water can also accumulate during the transportation process from the refinery to the wholesale distributor and the retail pump. Condensation from humid air can collect on the inside walls of a fuel tank, and rain and sea spray can enter the deck fuel fillers and tank vents aboard a yacht.
Eliminating the water in fuel is the first step in putting microbial colonies at bay. Traditionally, this has been accomplished after the fuel leaves the yacht’s fuel tank, but before it reaches the main engines or generator.
Primary fuel filters, such as Racor and Separ brands, are plumbed in between the fuel tank and the engine. These primary filters separate water from the fuel using turbines or vanes that generate centrifugal force as the fuel flows through the primary filter housing. This rotational force removes water droplets from the fuel that fall to the bottom of the collection bowl.
Both manufacturers use additional proprietary baffles or water-blocking filter media to coalesce and remove smaller water droplets. Both Separ and Racor units contain disposable filter elements, which also collect solid contaminants. Racor primary fuel filters use three stages of filtration that removes 99 percent of water from the fuel flowing to an engine, according to their technical services department. Separ primary fuel filters use a five-stage filtration process, which has been verified to remove 99.9 percent of the water entering through the fuel line.
A newer company, Dieselcraft, takes a different approach to water separation. Dieselcraft dubs its water separators as “filter-less diesel fuel purifiers”. These fuel purifiers do not use disposable filters or centrifugal force to remove both water and particulate contaminants that are carried through the fuel line. So how does the fuel purifier work?
Dieselcraft’s website explains that the first stage of purification “is based on surface tension principle. Since diesel and water have different surface tension as well as density, when a mixture of diesel and water is spread over a large area, water droplets and large solids will separate from the fuel.” This separation is accomplished by changing the direction of fuel flow within the purifier.
Forcing the direction of fuel flow to change causes the fuel and water molecules to separate, based on their specific gravity. Specific gravity is a measure of density of a substance. Since clean diesel fuel is less dense than water and particulates such as sand, rust and metal, these heavier contaminants collect in the purifier’s reservoir for disposal.
A second stage then removes additional water by using activated alumina. This compound is manufactured in a way that produces very porous small spheres or beads. These pores, that tunnel through the beads, trap water and other impurities. Activated alumina has been used for years to remove fluoride from drinking water, and also as a desiccant to remove moisture from the air.
According to Dieselcraft, “before the fuel can exit the purifier, it must pass through a barrier of activated alumina. This is used to trap any residual water and solids that has not separated from the diesel fuel”. Their complete process removes 99 percent of free water from the fuel line.
For marine applications, Dieselcraft recommends installing the fuel purifier between the fuel tank and the primary filter.
Whether it is cost effective to have both a fuel purifier and primary filter connected inline between a diesel fuel tank and engine is open for debate. Both Racor and Separ units also remove at least 99 percent of the water and large amounts of organic and inorganic contaminants, as well. Therefore, the fuel purifier seems a bit redundant.
Water removal from diesel fuel is best accomplished during regularly scheduled fuel polishing that is part of a yacht’s preventive maintenance program. The fuel polisher should have a separate pick-up tube within the tank that reaches to the bottom of the fuel tank. This dedicated pick-up tube sucks up all the water from the bottom of the tank. The fuel line pick-up tube that feeds the engine is located many inches above the bottom of the fuel tank and is purposely designed that way so heavier fuel contaminants, such as water and sediment, stay at the bottom of the tank and are not pulled up into the fuel line feeding the engine.
Capt. Jeff Werner has been in yachting for almost 25 years, and is the owner of Diesel Doctor (MyDieselDoctor.com). All Triton readers receive a 10 percent discount on online orders. Comments are welcome below.