I have to reiterate based on over 30 years of filtration engineering
experience: If you are in need to screw around with filters then you
havent done your proper maintenance by periodically opening and
cleaning out the fuel tank .... gums, goos, and incomplete
polymerizations of 'old dead fuel'. A filter is simply NOT a
substitute for proper and routine tank maintenance.

A 2 micrometer filter in an in line filter train is simply gross
overkill that will eventually and needlessly fatigue the diaphragm of
your mechanical lift pump. You simply CAN NOT substitute the same size
(surface area) filter from a 15µM to a 2µM filter without adjusting for
the opering differential pressure across such filters. Filters are
sized according to flow rate vs. operating differential pressure - get
the technical specs from the manufacture before you 'intuitively' screw
arround and make a needless & complicated 'mess'. A 2µM filter will
demand approx. 7X the surface area to remain at the same operating
differential pressure of a 15µM. The service life penalty is about
25:1 without adjusting for increased surface area (the permeability of
a 2µM is about 7X LESS than a 15µM). 15-20µM being 'the most damaging
(hard) particle for an internal combustion engine.
Most particles found in fouled fuel oil tanks are typically
agglomerated (stuck together) very small particles that when trapped
on a filter media and subjected to large pressure differences across a
filter, simply 'extrude' deeper into the filter media (thus blocking
it) or simply extrude all the way through. these 'particles' are the
gums, etc. that dont burn very well and pass through the combustion
chamber only to 'coke' in hot exhaust manifold or water injection
elbow. Filtration is NOT the solution; constant maintenance (cleaning
the tank) and only using FRESH fuel is the obvious solution. High
usage of filters with fuel oil is a SYMPTOM. A blocked filter is
telling you you have a dirty/fouled tank.

BTW
I run an independent constant recirculation polishing loop @ 5-10µM @
~3 GPM and the inline delivery system only needs a (properly sized) 2µM
followed by a grossly undersized 2µM 'choke' filter. All the 'work' is
accomplished by the CHEAP recirculation/polishing filter elements.
The system works so well that I am removing all the complicated in line
parallel filters, valves, etc. etc. I do clean out the tank every
other year.
I NEVER fill the tank unless I NEED that much oil. Condensation (water
-oil phase equilibrium, actually) uptake of water is NEVER a problem as
I use a desiccant vapor trap on the vent. I only have onboard what I
need and a little for reserve. I never buy from a marina and usually
haul in the oil from a truck stop (cheaper and FRESHER). Fresh oil is
important as in summer condition diesel only last about 6 months before
it begins to 'particulate', etc.
(I dont pay for my filter elements and professionaly "Im supposed to be
a 'filter expert"). Filters are NOT teeny screen doors, there's much
more to filters than retention rating ( & most 'ratings' are arbitrary
BS).
;-)


In article , Wayne.B
wrote:

On Tue, 09 May 2006 13:17:35 -0700, RW Salnick
wrote:

It is certainly true that with a pump or two and 10 or more
valves, you can set up for almost anything. But will you get it right
in the middle of the night? Years after you designed the system?

Good points. Speaking from personal experience, it is very easy to
open or close the wrong valve in the heat of battle (big seas,
sputtering engine, etc.). That is a bad time to accidently introduce
air into the fuel system. Don't ask me how I know. :-)

In addition to keeping things simple and intuitive, it is important to
rigorously follow a tried and true procedure so that no ad libbing is
required. It is also worthwhile to invest in a nice set of engraved,
color coded labels for non-obvious valve positions.