In article . com, Skip
Gundlach wrote:

So, two questions from all this.

1) Is my polishing setup appropriate - is the 30 followed by the 10 a
good practice?
This is probable great overkill and will reduce the overall efficiency
of the 'turnover' of the recirculation system. A recirculation
polisher is effective because it can 'turn-over' or pass a LOT of fluid
through the filter set - depending on capture by all the capture sites
in the filter media that are much smaller that the 'rating'. Adding
'sequential' filters will drastically reduce the recirculation volume
..... and the system will take MUCH LONGER to turnover and down to
'acceptable' resident particles in the tank (a 'mathematical anomoly'
of recirculation filtration).



In a high turnover recirculation system, adding additional filters will
add flow resistance which will slow down the 'turnover'. A nominally
rated 10uM filter is probably closer to 30uM on an absolute basis, plus
the 10uM filter will have smaller diameter cellulosic fibers than a
30uM nominal. I'd go with the 10uM nominally rated filter even though
a 10uM filter will have approximately 1/3 the flow capacity of a 30uM.
(Cavaeat: if the system is fouled or if you havent cleaned the tank in
some time ----- indications a repetetive plugging of the main line
racors, etc. and you're too lazy or cant clean the tank--- then use a
30uM to 'hog' the system down to low particle levels THEN use the 10uM
to clean-up further. If you use a 30 immediately followed by a 10 it
will probably take 10 times as long to do the same job as when you use
'single' filters in a recirc. loop. .... unless you have a 'humongous'
pump to do all the 'work'.
Id also do this in an independent loop being careful to discharge the
recirculation loop near the bottom of the fuel tank or directly onto a
side wall to minimize 'whipping up a froth' of air-oil bubbles.
Obviously air bubbles being entraned into the main fuel line will
eventually separate into large bubbles and eventually 'stall' the
engine or fuel system .... 'flooded discharge' from a recirculation
system is a 'necessity' or you may have to put in a 'air bubble trap'
on the main fuel line. Keep it simple and be sure of a flooded
discharge or alternatively discharging onto the tank wall.

Filter 'ratings' in such 'fuel' filters are extremely 'arbitrary' and
usually NO realistic connection to the 'actual' removal of the filter
!!!!! Even the technically superior Racors are probably no more than
95% efficient at their 'rating'. .... meaning they can pass a
'basketball sized' particle and still be honestly rated at whatever you
but ..... the rating is '% weight removal' at the designated particle
size.

Recirculation filters should be set up as PRESSURE FEED not vacuum feed
where the pump is at the END of the circuit ..... the filters will be
vastly more efficient versus on-stream service life due to the better
deposition of particles ON the filter surface than IN the filter when
in vacuum feed mode. The Walbro has an integral screen of about
100-200uM so you dont have to worry of large particles harming the
pump; although, you must remember to clean the integral pump inlet
screen occasionally. Do NOT use compression fittings on a pressure
feed system single or double flared connection (or better) only .... in
fact you should probably replace ALL compression fittings ANYWHERE in a
fuel system as they ALWAYS eventually leak (air gets sucked INTO the
system on a leaky compression fitting when the system is in vacuum
mode) over time.

2) For those who have done it, or if there's still a professional
filtration person looking into this group who can give empirical
commentary vs usage experience, will I be changing 2s in the dual Racor
setup often, or will the polishing likely reduce the particulate to
that or below?
If the recirculation system is well designed and maintained you
probably NEVER will encounter ANY challenge of particles to the racors.
The recirculation system (if ON often or anytime the engine is running)
will keep the particle background in the tank to well below submicronic
levels thus no challenge to the Racors. Racors however willl
eventually fail due to being soaked by free or emulsified water
(causing 'digestion' of the cellulosic component of the filter media)
and 'flexure fatigue' of the pleats due to pulsations coming from the
mechanical lift pump on the engine.
Whats NICE about a recirculation system is that you can remove the
majority of 'crud' in very 'inexpensive' filters and keep a single
racor (and engine mounted 'last chance' or 'guard' filter) from
plugging. You dont need prefilters (primary) in a system that has an
adequate recirculation filtration system. In such a system you can
even run a 'hard line' bypass (no filter) when changing a plugged racor
as the fuel tank will have essentially ultra filtered oil and you can
run for sseveral minutes with this clean already filtered oil as you
change out the racor.
The dip tube of the recirculation should pick up the fuel at the VERY
bottom of the tank to ensure that youre down into the crud and water
thats usually in the bottom. The water can be removed in the
recirculation loop by simply adding and 'empty' filter housing and
letting the water 'settle out by gravity' in the empty housing, etc.
..... a clear plastic 'tail' tube with a valve on the bottom of the
empty filter housing will show when there is water in the empty
'knock-out' pot.

The better you filter the tank contents removes the submicronic
particles that are the nucleation sites upon which larger and large
particles 'grow'/aggloerate. Stands to reason if you continually
remove these very small particles ... then you will have infinitely
less particles growing. The caveat here is that you still have to get
inside the tank every few years and clean out all the crap thats stuck
to the walls .... but not as often as if didnt have a recirculation
filtration system.

The best reason for having a high turnover recirculations system is
when due to degrading oil (cracked oil, or oil thats becoming fouled
with microorganism growth) and the crap has formed on the walls .....
even if the crap does break loose from the walls during a heavy sea
state the reciruclation will QUICKLY restore the tank back to low
particle levels. STill need to clean the tank occasionally.

The BEST way to operate the fuel system is to continuously MONITOR the
main fuel system filters with a vacuum or pressure gauge (measured as
pressure drop across the filter versus maximum engine rpm) ... so you
know WHEN to change the filters. Ditto on the recirculation system.
ALL filters should have an operational 'recommendation' of liters per
minute versus 'differential pressure' .... when the operating flow to
the engine is getting close (flow through the filter vs. what the gagte
is telling you - then its time to change the filter ---- READ the
technical specification that come with the filter or go to the filter
manufacturers website for the 'tech' / flow data. Be aware that the
tech data for flow vs. 'delta P' should be for *fuel oil* and NOT for
water --- big difference in flow/pressure requirements. If the tech
info is in 'water flow' contact the filter manufacturer and get the
'fuel oil' flow rating. Change the filters when the pressure/vac.
gage shows (versus the performance curve of the filter) that the flow
rate 'could be' 200-150% of flow of the engine demand at full throttle
..... look at the engine fuel consumption vs. horsepower curve and then
compare to the fuel filter(s) performance (flow vs. differential
pressure) curve. Size the filters based on the 'performance flow rate
vs. operational differential pressure curve .... NOT the maximum flow
rate on the 'box' .... when filters get dirty their flow begins to shut
down .... plan on it and know the gage pressure when you should change
the filter.
Not all the particles that a filter 'captures' are 'hard' particles;
many of the particles retained will be 'soft' particles and will begine
to 'extrude' through a filter if the differential pressure across the
filter becomes 'high'. Best is to maintain your own 'history' of
operation (make notes, etc.) and then stick to the maintenance & filter
changeout depending on YOUR operational history, etc..
No sense having ANY filter installed and not knowing WHEN to change it
...... other than having a stalled engine !!!!!!!!! Otherwise, you're
just throwing away good filters or risk stalling the engine (usually at
the worst possible time).

Before you add a recirculations system .... better to get inside the
tank and scrub out and mechanically remove all the crap .... then you
wont NEED all those expensive 'filters'. Filters only remove
'symptoms', the cause is usually a dirty tank or taking onboard
extremely dirty fuel.

When to NOT buy fuel: before pumping into the tank, take a clear
glass, pour some fuel into to it and hold the full glass between you
and a strong light. If there is any 'haze' to the fuel .... get your
fuel somewhere else. When to clean out the tank .... ditto with the
glass in front of strong light.

Hope this make 'sense'.
;-)