Seems to me if the filters are clean and if there is a screen or coarse
filter to protect the pump the differences between having the fine filter
before or after the pump are probably academic. I don't know the pump
details or characteristics, but pumps need to have their inlet pressure
above some minimum figure - net positive suction head - or they don't work.
And it's much easier to find leaks of fuel out of a pipe than air leaks into
it. If it leaks fuel it's still working, if it leaks air in it probably
isn't.

So I'd think more about troubleshooting the system when there has been some
bad fuel and the filter pressure drop is getting high --- I'd like to see
the pump protected against things which might damage it, then a pressure
gauge , then the finest filters. It might not be the best arrangement in
terms of emulsifying water, but I'll bet it's the easiest one to diagnose.
Mark the pressure gauge with new pump and a clean filter, second mark
corresponds to max filter pressure drop. If you really want more assurance
that it's running OK, either add a pressure gauge on the suction side of the
pump to prove the inlet strainer is not blocked, or a delivery side sample
point you can use for a flowrate check. I'd go for the flowrate check, and
make the inlet strainer as coarse as possible - it's a strainer to protect
the pump, not a filter ....

David





"Rick" wrote in message
hlink.net...
Steven Shelikoff wrote:

IOW, even if the pump is past the filter drawing fuel through it, the
filter is still in "pressure" mode because it's really the atmospheric
pressure pushing fuel through the filter.

The difference is that if the pump suction pulls water and
fuel directly from the tank it will do an excellent job of
mixing it up to form an emulsion that will not filter out
very effectively.

The path should be, a basket strainer to catch the chunks, a
separarator/filter to eliminate the bulk of the water and
the smaller suspended particles, the pump, then the finer
stages of filtration.

This is all assuming you don't have access to a centrifuge
which is really the best way to handle the process.

Rick