T&T: Installing an electric fuel pump for priming and backup

[Candy Chapman and Gary Bell]

Bob C. asked:

I would like some advice on where to install the electric pump in the fuel 
line. <snip> I have a Racor before the fuel goes to the engine.
Should I install it before or after the Racor?


Before the Racor.  Generalization for pumps, they far better tolerate 
loading up the output than the input.  So put your pump before the 
filters.  If you are worried about crud messing up the pump, add a small 
strainer upstream.  Side benefit is that you can use a manual switch on 
the pump to refill the filters after an element change, and of course 
use the pump to bleed air out at the engine.  Think about it.  The 
suction side of the pump is likely running at significantly less than 
ambient air pressure -- and the output at significantly more.  If the 
Racor were on the suction side of the pump, and if there were a tiny 
leak (say after a filter change), air would enter the fuel stream, 
crippling the pump and the engine.  If the Racor were on the output side 
a similar leak would cause fuel to dribble out, leaving the pump, filter 
and engine still running.  Imperfect in either case, but easier to 
handle in the latter.   Might suggest a dedicated drip pan below the 
filters too....

Cheers,
Gary Bell