Even high-quality diesel may contain trace amounts of water, whether it is water in the humid air entering through the fuel tank vents or condensed water in the large fuel tanks where diesel is stored at gas stations. However, in terms of fuel purity, advanced common rail diesel injection systems with injection pressures up to 2500 bar have higher requirements than simple mechanical systems.

Tiny dust particles and water droplets can damage the components of the fuel circuit and even cause system failures. Another challenge is the composition of modern diesel fuels, which have undergone significant changes in recent years: they contain very little sulfur, while the proportion of biofuels and additives is higher. This leads to the formation of very small and stable water droplets in diesel and requires new water separation techniques. The Merrill fuel filter adopts a three-stage water separation method, which can separate more than 90% of the water in the fuel.

In the first stage, the filter medium continuously removes solid dirt particles from the diesel fuel. The second stage uses cohesive materials. It even intercepts the tiny water droplets in the fuel/water lotion and combines them to form larger water droplets. In the third stage, the hydrophobic screen layer ensures that the increased water droplets do not enter the injection system. Gravity collects the separated water in the collecting chamber of the filter module. Once manual drainage is required, the sensor will send a signal.

Merrill can separate more than 90% of water from diesel fuel at current gas stations, even if it is only a ten micron droplet. Even with a loaded filter element, it can still operate until the end of its service period. The single stage and dual stage concepts in the market only achieve relatively low separation efficiency, which can only reach 35% to 40%, and therefore cannot provide sufficient reliable protection for modern fuel injection systems.