Avoid (DO NOT USE) 'toilet paper' AT ALL COSTS in a fuel system.
1. The cellulose in toilet paper will 'digest' when in contact with water and that 'water' may be the emulsified form which is not 'observable' by the naked eyeball. Toilet paper is MADE to 'fall apart' in contact with water ..... in a tank that is vented to 'atmosphere' you WILL have lots of water (in various 'phases') 'mixed with' the oil (by chemical equilibrium).
2. Toilet paper when used as a filter is not 'fixed' .... the fibers are only 'felted' and with increasing pressure against them will tend to 'slip' thus allowing some/most/all the trapped debris to become released. Whjen the cellulose becomes 'digested' from contact with water .... the cellulose also become 'particles'!!!!!!
3. the net result is 'water digested' cellulose particles, releasing of already trapped particles back into the system flow under increasing differential flow across the 'filter'.
OTHER
3. Dont use an 'expensive' pleated type filter in a recirculation system .... too expensive. There are many manufacturers of economical 'graded pore density' filters .... the 'pores get small the further you penetrate INTO the filter media.
Just about 'any' manufacturer of 'industrial' filtration will be able to supply your needs. Gulf Coast, and other 'oil patch' and home heater filter manufacturers wont have the efficiency (hence cost effectiveness) of the 'industrial' filter manufacturers. eg.: The 'parent' company that owns RACOR has a very large 'industrial' filter enterprise - Parker.com.
Stay AWAY from HomeDepot and Lowes 'filters' .... cheap 'garbage' made in asia and with VERY variable and non-repeatable retention characteristics.
4. A recirculation system for a boat application should be HIGH TURNOVER flow rate. If youre not giving approx. .25 to .5 gallons recirculation flow per 10 gallons and filtering to a level of 2 to 5 times the µM rating of your 'final' filters ..... you are mostly wasting your time and money. As much as possible in a Recirculation system, AVOID all 'fittings'. "Fittings" cause 'pressure drop / reduced flow'. Instead use bent 'long radiused' sections of tube instead of 'elbows'. Use the LARGEST diameter tube/pipe possible.
It takes WORK (energy) to do filtration and if you design a system that has lots of 'pressure drop' (friction), the minimal amount of pump energy will be left for 'filtration'.
5. As in ALL CORRECTLY designed filtration systems ..... the pump goes at the BEGINNING of the flow and PRESSURIZES the system, not at the end in ill-conceived and poorly engineered (but widespread) 'boat systems'. You should need to 'protect' the pump install a suitable strainer (100-200µM) between the tank and the pump; many of the Walbro type transfer pumps have 'integral' strainers already built in to the pump.
In 'vacuum' service (a single stage pump at the end of the loop) will 'stall' (no flow) at about minus 4-6 psi of 'vacuum'; in pressure mode (pump at the 'beginning' of the loop) most 'transfer' pump can deliver up to or more than 30 psi (most industrial filters can withstand between 50-70 psi before breaking). The result will be that the pressure feed pump will deliver more absolute 'throughput' to the filter (about 5 - 10 X more than a vacuum motive system) before the filter 'plugs' (reaches terminal differential pressure) .... and for more technical reasons than just the pump 'stalling'.
6. DO NOT 'integrate' a recirculation system into the 'main fuel delivery system'; keep the 'recirculation system' INDEPENDENT (OK to apply 'crossover branches' for emergencies).
The 'recirculation polishing' should be high volume flow, the 'delivery' should be 'low flow' (capacity to about THREE to FIVE Times the engine fuel consumption at WOT (wide open throttle)
My 'personal' fuel system documentation is much too large to be uploaded on this site so if you are interested in 'state of the art' for 'small boats', email me at RhmpL33(AT)att(DOT)net.
(Since Im 'at sea' at present, it may take a while for me to reply.)
regards
RichH
