I recently purchased a 1972 Columbia 45 with an original Perkins 50 hp marine engine 4-108 I want to insert an inline fuel polishing system between the diesel uptake line and the manual lift pump on the engine. The two additional filters will be a racor primary(30 microns) and a racor secondary(10 microns) in series followed by a fuel pump (walbro FR series?) that will have 2 lines out; 1 to the manual lift pump on the engine and the other with a check valve to the fuel return to the tank. The check valve should keep positive pressure on the lift pump. I want to maximize the polished fuel flow returning to the tank but I am concerned about the psi exurted on the lift pump by the new pump installation. Should I be? What was the rated psi on the low pressure side of the fuel system at the time of installation? My thinking is that I should meet this with the new installation. thanks for any info/advise. Mike the Canuck