Fuel Polishing - High Flow rate through filter

[swinsail]

Sorry for yet another fuel polishing thread, but I haven't been able to find an answer to this question as yet . . . .

My boat has a 20 litre day tank in the engine room which is filled from either of the 2 main tanks (200 litre and 300 litre) by a Johnson Flexible Impeller transfer pump (F3B-19/12V). This pump has a transfer rate of around 14 litres/minute (3.7 gpm). The fuel path is from either tank, through a CAV filter with glass bowl, through the pump, and then discharged to the day tank. Adding a 3 way valve after the pump would allow fuel discharge to be directed back to the tank and hence complete a fuel polishing circuit however I am unsure of the consequences of such a high flow rate through the filter. The CAV filter is rated at 45 litres/hour whilst the pump is moving 840 litres/hour. The filter has 2 main functions . . . particle removal (rated at 7-10 micron) and water removal via the bowl. The pump is rated for continuous duty, but at this high flow rate is there anything to be gained using this setup or do I just need to install a low flow rate electric fuel pump in circuit?

The boat is a 38 foot yacht. Engine is a Thornycroft 108 (very similar to a Perkins 4108)


Thanks

[Scott Berg]

at the risk of sounding glib 'smaller pump' or 'bigger filter'

[Lepke]

If you run the fuel thru a bowl sediment filter too fast, water may not have time to settle out and particles bigger than 7-10 micron size may be pushed thru the filter. A bigger filter would solve your problem. Running the current filter with a high volume won't clean anything. The slower fuel, oil, etc., is passed thru a filter, the more dirt is captured.