Tank Discharge Locations
I have a 2006 American Tug 41. I have just purchased a ESI polishing system. My vessel, Peregrine, is on the hard Oct thru April in the North East. I felt the polishing system could be utilized during the winter months to clean the fuel. In my conversation with ESI, it was suggested that the returns be located so that the will go near the bottom of the tank to create as much turbulence as possible.
I have two 320 gal tanks, one port and one Starboard. The top of the tanks are not accessible. I do have a spare 3/4 NPT port located about 1" from the top of the tank on the opposite end from the fuel supply which is located at the bottom of the tank. ESI has available a fitting that requires a larger hole be placed on the tank that has a dip tube that will go down to the bottom of the tank. They tell me it is leak proof, but I would prefer NOT to drill this hole. NOW TO MY QUESTION.
What is your feeling of leaving the discharge on both tanks at the top or do you know of a fitting that might work with out drilling a new hole in the tanks. Again the Fitting there is a female 3/4" NPT
Jim Stony
Jim:
Thanks for posing this excellent question. I’ve found that the majority of fuel polishing systems I encounter here in the boat yard (other than the ones we install :)), are not plumbed in such a way as to maximize their efficiency. That’s a fancy way of saying they are often strangled by undersized plumbing or they are incorrectly plumbed to the tanks.
For a fuel polishing system to work as well as possible, two criteria must be met. First, the plumbing should be entirely independent from any existing engine or generator fuel supply or return plumbing. Why? Existing plumbing fittings are often too small to handle polishing system volume and the polishing system plumbing may compromise the engine or gen’s fuel supply or impede its return (this can cause injector pumps to malfunction). Second, the polishing system’s supply and return plumbing inlet and outlets should both be located close to the bottom of the tank. This ensures that the debris and water are being picked up by the polisher and it sets up a current that will scour the bottom of the tank, picking up loose debris. Additionally, the problem with returning fuel to the top of the tank, for both polishing systems and engines, is that the splashing created by this practice aerates the fuel. Air entrained within the fuel, if it should make it to the injection system, will cause erratic operation and it hastens the fuel’s oxidation, which essentially makes it age more quickly.
Given the choice, I prefer to install fittings at or near the top of the tank and then utilize drop tubes the draw and return fuel from the tank’s bottom. This minimizes the possibility of leaks and still ensures efficient fuel polishing.
Steve C. D’Antonio, Technical Editor