On Thu, 08 Jan 2004 14:53:44 GMT, Rick wrote:

Steven Shelikoff wrote:

Well, now I have to ask why the pump should be before the finer stages
of filtration.

Because you can install canned filters which are rated for
high pressure downstream of the pump, on the pressure side.
The filters on the suction side are fairly coarse, produce
little resistance to flow until clogged, and can perform the
initial separation of water and solids.

wouldn't matter where the pump is. Of course if it can't do that (not
enough suction for all the stages before it) then you'd have to move the
pump up in the stream like you suggest above.

If the pump was upstream of all filters, so that it sucked
through them all, the differential available is pretty low.

That all depends on how many "all" is, the max pressure differential you
want to operate at and how much vacuum the pump can draw. 2 stages
should be fine. 3, probably not.

That is why most installations use Racors on the suction
side for the reasons I have given and then the final filters
are can filters on the pressure side.

I have 3 stages with an electric pump between the 2nd and 3rd and then
the engine lift pump after the 3rd. Works pretty good. The only time
it stopped working, leading me to thinking there was a vacuum leak, was
when the tank vent clogged and vacuum built up in the tank to the point
where fuel couldn't be drawn out anymore. Problem solved temporarily by
opening the filler.

Steve