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With the exception of the notorious slip-on-a-hose-over-a-cut-tube connection .... all such fittings are 'ring seal' (metal-to-metal) sealing; if you NEED a sealing 'aid' to stop such leaks, the 'fitting' probably has become 'deformed' at the 'ring seal' portion and most probably should be entirely replaced .... or in the case of the equally infamous 'compression fittings' the copper tube should be 'trimmed back into 'fresh' copper and a new brass 'ferrule' used.
 

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PRESSURE FEED SYSTEM, NO VACUUM , NO VACUUM, ALL PRESSURE FROM THE PUMP INTO THE FILTER. PRESSURE GAGE!!!!!!!!!
Make all the connections 'bombproof' so you dont ever have a leak. Vacuum Feed filter systems are TERRIBLE and VERY inefficient.
Is it ok to pressure feed a Racor 500? I ask because I have a spare 500 that I was planning to use in a polishing circuit and, "Turbine Series filter assemblies are designed to be installed on the vacuum side of the fuel transfer pump for best efficiency..."
 

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Slightly different situation, not polishing but feeding a day tank.

What harm in using a 2 micron filter in the feed circuit to a day tank?
 

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Rx: So, if you for some reason think that a 2µM filter is 'perfectly OK' to replace a 10µM filter (in a 20µM spec. engine), to do the same system design job as the 10µM ..... you will need to increase the surface area of the 2µM filter by a factor of 5 ... OR FIVE 2µM filters in a parallel arrangement .... to equal to one 10µM filter.
Lucky for us running relatively small engines these filters are designed to run 300HP monsters. We will not see enough restrictions on a 2micron filter to matter, until it becomes blocked. I would rather change the filter every 100 hours then change the fuel pump every 1000 hours. FYI The system that came on our yacht has one suction side racor, and one engine mounted pressurized filter. 5micron and 2 micron respectively.
 

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Schooner Captain
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The 2µM in vacuum mode filtration will have a 5X operating differential across the filter than a 10µM .... this means to deliver the SAME flow demand, the 2µM will cause the lift pump to develop 5X MORE vacuum.
Its not going to be anywhere close to linear. Otherwise if you were drawing a negative 4psi before, your would draw nothing after....
 

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until it (begins to) become blocked


... and that blockage will approach an exponential rate ('time' to the ^-3/2 power) of blockage.

I would recommend that you consult the (Racor, etc.) published flow rate vs. differential curves - Q/∆P of the filter 'cartridge'; otherwise, youre just 'guessing'.
 

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Slightly different situation, not polishing but feeding a day tank.

What harm in using a 2 micron filter in the feed circuit to a day tank?
No harm at all, especially if the day tank is operated on a sometimes long interval unused basis.

The benefit of a 2µM in such day tank, etc. situations is that the common fungal 'spores' found in diesel oil and which are the usual contaminant are in the range of 3 to 4 µM, therefore removed by the 2µM. ... So, for a single pass filtration system (filtered once and done), you'd have a very high probability of at least minimal fungal growth during long periods of system shut down.
For a large day tank, Id advocate the installation of a remote hydrophobic 0,2µM bio-blocking filter (with low value 'rupture disc') on the tank atmospheric vent (if vented) for 'important' installations - prevents the aspiration of fungal and bacterial spores directly into the tank during tank draw-down.

hope this helps.
 
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