Fuel/Water Separators

Water in fuel can cause serious maintenance issues, such as enhancing corrosion of fuel system components and accelerating wear on fuel components by reducing lubrication. Additionally, water in fuel promotes microbiological growth, which may plug filters prematurely and adhere to fuel system components.

Water can be found in fuel in three different forms: dissolved, free or course and emulsified, says Robert Braswell, technical director of Technology & Maintenance Council (TMC). A technical council of American Trucking Associations (ATA), TMC is North America’s premier technical society for truck equipment technology and maintenance professionals. ATA is the largest national trade association for the trucking industry.

Dissolved water - The presence of dissolved water in petroleum-based fuels usually has an upper limit of 100 to 200 part per million (ppm), Braswell says, but biodiesel can contain up to 1,500 to 3,000 ppm of dissolved water. Dissolved water is not known to have any damaging effect on fuel system components.

Free or coarse water - Free or coarse water does not have a universal definition, he observes. However, these terms are typically used to describe water that is not fully dispersed throughout the fuel.

SAE (Society of Automotive Engineers) J1839 test standard, “Coarse Droplet Water/Fuel Separation Test Procedure,” defines coarse water as having a mean droplet size of 180 to 260 microns. J1839 calls for a test apparatus that generates this range of water droplets to approximate field conditions, which is then used to determine the undissolved water removal performance of a fuel/water separator.

Emulsified water - Emulsified water does not have a universally accepted definition either. Nevertheless, says Braswell, this term is typically used to describe when water and fuel form an emulsion in which the water droplets are so tiny that they remain in suspension for a very long time. In high enough concentrations, it can make the fuel appear milky.

Test standards SAE J1488, “Emulsified Water/Fuel Separation Test Procedure,” and ISO (International Organization for Standardization) 4020, “Road Vehicles - Fuel Filters for Diesel Engines - Test Methods,” are used for quantifying filtration performance with emulsified water.

“Fuel/water separators are designed to remove free/coarse and emulsified water,” says Braswell. “They typically employ one or more methods to remove these types of water. Gravity is commonly used to aid water separation and precipitate water removed by the filter into a settling chamber where it can be drained during maintenance intervals.”