Thanks folks for responding
I chose the Walbro because it was a marine rated diesel 12V pump with a separating screen filter on its intake for primary screening of junk (70 micron) prior to the RACOR.
Using a Racor in a fuel recirculation polishing system is a very expensive filter to use in a recirc. system. A Racor type filter is for removing a VERY small amount of debris from a relatively large system (0.005% or typically 30-50 GRAMS of crud is about all you get from the typical RAcor).
I'd recommend to
1. 'up' the throughput of the pump (typically 3 gallons per MINUTE per 100 gallon tank is 'reasonalbe'). The newer Walbro pumps are 'outstanding' vs. long service life.
2. Install a STANDARD INDUSTRIAL filter housing (industry standard is for use of filter cartridges of 10" length and 2.75" (or 2.5") outter diameter.
I'd suggest Shellco Filters Shelco Filters
Other: most industiral filter housing have 1/4" connection on the top/bottom of their housings
There are other manufactrers of industrial filtration products. Dont use HomeDepot stuff nor filters that are for home heating oil.
3. Use STANDARD industrial filter cartridges (available worldwide from zillions of manufacturers) Size the 'retention rating' @ 5X the retention of your FINAL filter in the RACOR Set (not including the OEM engine 'guard' filter. Choose a 'graded pore density' filter ('pores' get smaller as the fluid travels through the filter media). A graded pore density filter of polypropylene melt blown fiber should cost about $8 to 15.00 ea.
These are usually 'honestly rated' for their ÁM (nominal) retention; should be at least 90% retention at the indicated 'rating'. Avoid Home depot and other hardware store unbranded filters - as their ratings are very variable. ... you want 'quality' not cheap.
4. The recirculation system should be totally isolated from the standard fuel delivery system AND with an independent pickup tube AT the very bottom of the tank.
5. Run the pump BETWEEN the tank and the filter housing (pump PUSHES the oil). Therefore in PRESSURE MODE the pump will not 'stall' (no flow) until the pressure differential of 'crud' on the recirc filter is about 50 psig max. If you run the pump in 'suction mode' the pump will stall (at about minus 3-4 psi.
In pressure mode, if the pump inlet screen/strainer becomes 'choked' with (hard) debris you will begin to see negative pressure (or a drop of differential pressure) on the gage (see 5a.). Most debris in boat diesel fuel system is 'soft/deformable' (cellular debris of funguses, etc.) and the pump 'screen' at 70 ÁM will usually 'chop up' the deformables.
You will get longer filter life, more total gallon filtered with 'pressure feed' than with 'vacuum feed'.
5a. Apply a pressure gage between the pump and the filter housing. When operating compare the gage pressure to the filter manufactures "flow vs. deltP curve" to monitor the flow and to know WHEN to change the filter. You many want to use an electrical differential pressure switch wired to an alarm .... hi and LOW pressure switch so you know when to change AND for safety/enviro issues.
Dont get 'locked' into using one particular filter manufacturer because of 'geometry' - the worlds industrial 'standard' for filtration is 2.75" dia X 10-20-30-40 inch length filters. Cartridges with FLAT neoprene rubber endcap gaskets are suitable, so is 'knife edge' cartridge sealing for such fuel filtration.
Ive Been very deeply involved in filtration engineering for over 40 years. Racor makes the BEST filters for the PRIMARY fuel line filtration. NOt worth it for 'recirculation-polishing' filtration. Parker(Racor) has industrial filter divisions (and distributors) that can fill your needs if you somehow need to stay with the Racor brand.
Dont buy from an industrial supply source that requires a 'minimum charge'.
hope this helps.