Fuel Polishing

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fuel_polishing.jpg
As they say, a good diesel will keep running as long as you supply air, keep it cooled and provide clean fuel.  Trawler tankage is necessarily large, which means fuel can be a year old (or more) before it is completely consumed.  Consequently, polishing is probably mandatory if trouble free cruising is on the program.

There are differing opinions on the level of filtration at what stage to use to polish, but we elected to polish at 30 microns, transfer fuel to the day tanks at 10 microns, and filter at the engine to 2 microns before passing the fuel to the standard CAT fuel filter.

The elements of Delfin's system include:
  • Polishing with a 1/3 hp 120 vac carbonator pump at 3 gpm
  • Transfering with a parallel 1/3 hp 120 vac pump on a time delay on, time delay off relay array
  • Twin Racor 1000 filters
The source and supply manifolds were fabricated of aluminum and powder coated, providing ports for transfer of fuel between Delfin's 7 tanks.  These tanks include a 250 gal stern tank, two 750 gal wing tanks, a 250 gal bilge tank, a 250 gal forward tank, a 100 gal day tank for the CAT and a 25 gal day tank for the boiler.

De-bug units were installed based on prior positive experience with the units (they actually seem to work).

The time delay on and off relays allow the system to be turned on or off for up to 999 hours or for as short as .1 seconds.  These can be set so that if the vessel is left for a period of time, the boiler day tank can be automatically filled, pumping a couple of gallons a day with the overflow emptying back into the wing tanks.  Or, while underway, the system can be on peridiodically to refill the engine day tank at the same rate the fuel is being consumed.  Sound complicated?  Well, it is, sort of, but once wired up works well.  This timer can be made from two Omron H3CA-A (http://www.grainger.com/Grainger/items/1A983) relays.  One is set as a time delay on, while the other set to time delay off.  Just punch in the timing you want, and these relays will run a very long time without any problem.  Instructions on how to wire up these parallel relays can be opened to the left.

The choice of two separate pumps at two separate voltages was driven by a desire to have a true continuous duty cycle pump for polishing hours at a time, which can really only be done with a 120 vac motor, while retaining the ability to transfer fuel if 120 vac is lost.

The 120 vac pumps are carbonator types which match the flow rate of one of the 1000 series Racor filters.  This motor and pump can also be ordered from Graingers (http://www.grainger.com/Grainger/items/3K987 and http://www.grainger.com/Grainger/items/6XE90).  It is very quiet in operation, as opposed to 24vdc pumps which sound a bit like a Harley taking off, and you can run them for days without it damage.
Fuel Polishing Techniques

Depending on the tankage arrangement on a vessel, it is best to use one of the bulk storage tanks, preferably one on the centerline, as the staging tank that holds fuel that is transferred to the day tank for running.  This tank can be polished for hours on end, resulting in very clean fuel available for the day tank.  This is a more effective use of a polishing system than trying to polish all fuel in all tanks.  On Delfin, we extensively polish one of two centerline tanks and fill the day tank from there.  When the wing tanks, stern tank or other centerline tank is nearly empty, we polish the fuel left in that tank to collect settled contaminants.  Since the tank is nearly empty, you get a number of cleaning cycles on the remaining fuel, and if this polishing is done underway, the sloshing at the bottom of the tank really stirs up whatever is there, making it possible to filter it out.