T&T: Installing an electric fuel pump for priming and backup (be careful!)

[Ken Bloomfield]

As regards the placement of an electric fuel pump in the fuel supply to a 
marine diesel, I would make the following cautions:

1.  Racor explicitely says that their 500 and 700 and 900 series of filter 
assemblies are for vacuum applications only.
2.  The pressure that an electric fuel pump can create can comprimise the 
filter element if used in the disallowed pressure mode, that is to say with 
the pump before the filter.

When used after the filter, the maximum delta-P that can be across the 
filter will be much less than if the filter is on the pressure side. When 
used to "push" through the filter, you can drive junk through the element, 
whereas when used to pull fuel through the element, the worse that will 
happen is the engine will be starved for fuel if the filter is too clogged.

I would be very wary about putting the pump before the filter.  My twin 
Perkins came with an electric fuel pump downstream (i.e. after) the primary 
filter (which is 30 micron) and before the lift pump.  It can be used as a 
kind of "boost" for the lift pump, or completely eliminate the lift pump if 
needed.  It is a flow through pump, so when no energized it presents no 
resistance to the path of fuel (at least in the normal "forward" direction).

Cheers,
Ken Bloomfield
MTOA# 2062
AGLCA# 3529
M/V Tellico Lady, 50' Marine Trader-Walkaround
Maryville, TN