In article . com, Skip
Gundlach wrote:



Is this the effective equivalent of what happens with resistors vs
capacitors in series and parallel? Putting these in parallel would
more than double the effectiveness, whereas in series diminishes the
effectiveness?
No not at all. Has to do with the laws of exponential decay .... the
decay of the absolute amount of particles in the tank. The reason is
that the faster that you 'dilute' the residence of particles the faster
the decay to some finite level of particulate; the slower the filter,
the slower the recovery .... a 1 uM filter will have approx.
1/15-1/20th the flow rate of a 15uM ; plus the 15uM filter will have
capture sites (at a low efficiency of 1uM). Reciruclation filtration
takes the advantaage of using inexpensive very high flow rate filters
to arrive a MUCH lower retention ratings as if you'd filter in a
'series' mode.




Hm. I've never cleaned the tank - and nothing I got in the otherwise
pretty complete records suggests it's been done in the last 15 years.
For whatever it's worth, however, we had a very rough trip over when we
took possession and brought it 500 miles through the nasty conditions
in the Gulf, and had no issues whatever; the filter, while dirty, shows
no lumps or identifiable spots.
Fuel begins to degrade at the interface between the fuel and water
layers by fungi and bacteria using the oil (and the tanks walls) as a
nutrient source. If the fuel is produced as distillate it will be more
stable from breakdown than a 'cracked' fuel. There's lots of opinions
from API engineers ab out what is happening versus decomposition but Im
one who considers that cracked fuel (the most common i n the USA
readily breaks down in heavy alkene fractions, etc. .... which do not
burn well in the combustion chamber and usually settle downstream in
the exhaust section as coke which can block the exhaust .... these are
probably the large 'liquid particles' that extrude through filters or
block them.

About the length of time to accomplish, I'm not sure I understand why
that should be so. I'm operating on the presumption, despite the
previous, that I have a lousy tank condition. The point of the 30
followed by the 10 is the presumption that I'll have crud which we'll
dislodge pretty quickly. The suction gauge shows a very low level of
suction, so I presume there's little obstruction. I don't know about
"humongous" as a pump, but it seems to be doing reasonably well so far
with the 30 followed by 10. I've not put a bucket under the output to
test what the actual volume is, but opening a small unused port on the
tank to see what's going on shows theres a notable amount of fuel being
moved.

When using two filters in series the purpose the first stage is to
protect the second stage and give life extension to the second stage
..... in a properly designed two stage system you want to aim so that
the particle distribution is such that both filters plug almost
simultaneously. You need some fancy instrumentation to determine the
actual weight - particle size distribution.


Hm, again. I don't have an easy means of doing the discharge you
suggest. Currently, the discharge is straight down - no tube, no
directional difference. The pickup is the same as the Racors, however
far down that is. We've never experienced (yet, of course -and all
this is in an effort to make sure we don't get the first) a clog in the
old (very rotted by the time I tore it out) fuel lines. However, an
inspection of the tank through that small port above showed no bubbles
evident. Dunno why, as it seems it should be happening, after many
hours of running the fuel through. The pump is evidently a diaphragm
variety, as initially it was very fast and noisy, but that was only
until it sucked up the fuel in the line and filled the filters,
whereupon it settled down very quickly to a very quiet pulsing sound -
so, perhaps that's why no froth?
If you 'drop' oil onto itself you will most assuredly mix up air into
the tank oil. When the engine is running this air will eventually
separate from the oil and form bubbles in the most elevated sections of
the piping. Depending on how and how much air comes out and is trapped
these collected large bubbles can 'accumulate' and eventually stall
the injector pump, etc. Not a good practice to 'drop' oil into a
tank, especially if you're pumpin about *3 gallons per minute* back to
the tank from a Walbro transfer pump. Flodded discharge from the
recirculation system is proper.


Hm. Makes the toilet paper and paper towel type filter seem more
effective, doesn't it?
No, Not al all as paper towels and especially toilet paper has no or
VERY little resin binder to hold the filbers together. This makes TWO
problems: 1. upon increasing differential pressure a non-resinated
'paper' will unload particles as the cellulose fibers flex. 2.
Cellulosic fibers that arent resin bound are easily attacked and
digested by water - toilet paper is *made* to fall apart after its in
water for a short time - if your ever have the chance to go to a
sewqage treatment plant you will find that there is very little
'visible' toilet paper in such plants .... by the time the toilet paper
gets to such plants its all essentially broken down into individual
fibers or is essentially dissolved. There is ALWAYS water (emulsions
and free water) in fuel oil that is stored long term - it gets in there
by chemical equilibrium (not condensation).



I admit to being entirely unknowledgeable about all this, other than
what I thought I remembered from discussions on filtration over the
many years I've been looking at it, before having a real life
application of my own. What I *thought* I remembered was that you
absolutely didn't want to have pressure on the filters, but suction.
And, I presume there's some explanation in fluid dynamics or some such
of which I am likewise totally unaware, but I don't know why it should
be one way or the other. Is it that particles are being sucked *in*,
vs pushed *on*, the filter? And, in the case of Racors, why is it that
they have to be suction?

With vacuum feed there is little tendancy of the particles to form a
'cake' of debris on the upper surface of the filter, so the cake forms
more INSIDE the filter taking up space and closing down the flow paths.

With pressure filtration the cake more readily forms on the upstream
surface ... and then for quite a while the 'cake' becomes the filter
media - ie.: the dirt is now filtering out more dirt. This is all
velocity dependent so the lower the flow rate (face velocity) the more
apt the dirt will form on the upper surface as a 'cake'. With higher
velocities (or with vacuum feed) the dirt gets driven deeply into the
filter media and quickly plugs it.
ed you

Heh. Well, so far, it appears that it's not well designed - though it
meets all the various inputs I'd stored over many years while getting
ready for this point. I even had a couple of what looked like
professional designs in pdf. However, my recollection has you with
umpteen years in the filtration biz (recalling some of the endless
threads with jax and and perhaps some others), so my presumption is you
come from an industry perspective, rather than conjecture...
Disagree .... as ANY mode of recirculation filtration is VASTLY
superior to 'in-line' filtration when it comes to keep low particles in
a tank. Hell, a pressure pot filled with pubic hair or shredded kotex
can be effective.
So, if I understand you correctly, I should either completely
disassemble my currently installed unit and start over, or, at a
minimum, reverse the flow, change the suction gauge for a pressure
gauge, and leave one of the canisters empty and, after lots of 30
filter hours, go to only 10 filter and replacements??
Nah, leave it alone. Next time you build a system do it the other way.
As I state ANY recirculation is a far superior approach.

probably NEVER will encounter ANY challenge of particles to the racors.

My intent and expectation is that it will be on any time the engine is
running, as well as any time we're sailing with full batteries (the
wind generator should more than keep up with the load, if there's
enough wind to be sailing). I'd assumed that would provide the very
best opportunities for clean fuel other than to have it running nonstop
(never mind how it's powered in that case...).
Dont do this 'stuff' blindly ..... use the glass and strong light.
Then you know what you are about.


Well, that's comforting to know - though, having already made the
investment, and installed, a dual racor (change on the fly), I expect
I'll keep it. However, I'll also keep a very close eye on the bowls
for water. Currently there's the flame-arrest bowls with not only the
spin-off-the-bowl, but a plug in the bottom. I believe I'll trade the
plugs for a valved nipple so I can drain and check what's there without
the flood which would result in removing the flame arrestor, or even
just the plug...
Those clear bottom racors will show you when to drain out any water
that gets trapped in them. IT sometimes takes a bit of time for any
emulsion and mixed-up large amounts of free water to settle out.



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.

In our particular installation, that's a bit challenging, as the only
access is in the top (bow) deep corner, 1.5", other than some major
disassembly. It's my presumption that it's never been done in this
boat...


My Racor setup has the same (make, model, not literally the same)
vacuum gauge as the polishing system. I expected to use that as my
guide - but it's vacuum...
Vacuum feed is OK for filtration, just *not as good* as pressure feed.
Vacuum feed on boats has been driven by the boat builders being cheap
and dirty ..... the engine comes with the lift pump and its just so
cheap and easy to add the filters and fuel lines to the 'other side' of
the pump. With a pressure feed system you need a (lift) pump at the
tank and bombproof tubes and fitting so that you dont inadvertently
fill the bilge with oil. With a vacuum feed system if you have a leak
the system sucks air and the whole system automatically shuts down ....
good for EPA and Coast Guard but not for a boat operator who needs to
keep moving.

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

Interesting - neither the Racors nor the other have any such data with
the documentation. IN the case of Racor, I have not had any luck
trying to get information about them, at all. However, the others are
rather more mainstream, so I might be able to discover something about
them...
Go to the Paker .com website (www.parker.com) then ----"marine" then
ultimately to the Racor Division... its all there in the 'technical
data' section .... or at least is was the last time I looked. Dont get
lost in the 'european' sub-website stay in the USA dcata sections of
the site. If you dont find the data, call Racor ask for an Application
engineer and have them send you the *flow vs. delta-P* curves for your
filters.

Phew! I only *thought* I thought like an engineer. I'm in way over my
head, here. I'm not sure there's much info on our 30 year old engine
WRT consumption/HP/pressure/vac. I'm pretty sure I'll have to go by
the seat of my pants for the first several changes, after which I can
have the baseline to use...
Get the data from Parker Racor ... or keep records and build an
operational history of your set-up.


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.

Heh. Fortunately, the polishing system filters aren't all that
expensive, and are huge by the Racor 500 standards of what will follow
all that polishing. And, of course, it was the symptoms, of which I've
had none, yet, that I was looking to address.
The RAcor 500 has huge comparative surface area .... that will allow
LONG term service life, especially if you engine is only drawing 1
gallons per minute at WOT.


;-)

Well first of all filters are not screen doors. The filter media in
fuel oil filters is a 'felt' made of microfibers bound together with a
waterproof resin.
Pressure feed and correct flow rate will establish that the flow is
very slow asw it crosses the face of the filter media. If designed
correctly the dirt will form a 'cake' ON the surface of the media ...
and the dirt will begin to filter out other dirt. If the velocities are
too great the cake will collapse and become very dense .... and the
filter will shut down/plug.
With vacuum filtration the cake forms IN the filter media, and there is
less space - because the filbers of the filter media are also found
there. Once the filter gets dirt IN the filter the fluid velocities
become higher and higher thus driving the dirt deeper into the media
due to the increased fluid velocity and quickly shuts down the fluid
flow because there are few flow paths still open.
In all filtration the larger the upstream surface area, the slower the
fluid velocity, the lower the viscosity of the fluid .... all make for
'happy' long lasting filters.
When selecting a filter always choose the LARGEST you can fit or afford
..... it will save you $$$$$$$ in the long term.

On Fri, 24 Nov 2006 18:08:07 GMT, Rich Hampel
wrote:

Well first of all filters are not screen doors. The filter media in
fuel oil filters is a 'felt' made of microfibers bound together with a
waterproof resin.
Pressure feed and correct flow rate will establish that the flow is
very slow asw it crosses the face of the filter media. If designed
correctly the dirt will form a 'cake' ON the surface of the media ...
and the dirt will begin to filter out other dirt. If the velocities are
too great the cake will collapse and become very dense .... and the
filter will shut down/plug.
With vacuum filtration the cake forms IN the filter media, and there is
less space - because the filbers of the filter media are also found
there. Once the filter gets dirt IN the filter the fluid velocities
become higher and higher thus driving the dirt deeper into the media
due to the increased fluid velocity and quickly shuts down the fluid
flow because there are few flow paths still open.
In all filtration the larger the upstream surface area, the slower the
fluid velocity, the lower the viscosity of the fluid .... all make for
'happy' long lasting filters.
When selecting a filter always choose the LARGEST you can fit or afford
.... it will save you $$$$$$$ in the long term.

That didn't really answer the question, which is WHY does the "cake"
form IN the filter media for vacuum fed but ON the surface for
pressure fed? I would think that, all else being equal, it would work
the other way because the pump is operating more efficiently with
pressure fed, so the velocity would be higher, driving the dirt deeper
in the media. Other than that, I don't understand how the felt media
knows whether the pressure differential across it is caused by
pressure on one side or vacuum on the other. Theoretically, it
shouldn't matter. So I'm just trying to understand the physical "real
world" process that causes it not to behave according to theory.

Steve

That didn't really answer the question, which is WHY does the "cake"
form IN the filter media for vacuum fed but ON the surface for
pressure fed? I would think that, all else being equal, it would work
the other way because the pump is operating more efficiently with
pressure fed, so the velocity would be higher, driving the dirt deeper
in the media. Other than that, I don't understand how the felt media
knows whether the pressure differential across it is caused by
pressure on one side or vacuum on the other. Theoretically, it
shouldn't matter. So I'm just trying to understand the physical "real
world" process that causes it not to behave according to theory.

Steve

Possibly the Vac system is more constant, whereas the pumped system
pulsates, this may affect the level of turbulence causing the crap to
lie long ways across the filter, but with a more smooth flow (vac
system)the crap will align with the flow and penetrate deeper into the
filter media.

This is a blind guess, but may prompt someone who knows about these things.

I
Retention of particulate in/on a filter is an extremely complex entity
due to simultaneous and varied 'capture mechanisms'. that 'hold' the
particles in place: seiving - where the statistical pores of the filter
structure are smaller than the particle; inertial impaction - where the
particles leave the flow stream when the flow stream takes sharp bends;
aDsorption - where the particles are held to the filter media subtrate
by weak electronic bonding (van der waals forces); the formation of a
"cake" on the upper surface and into the upper 10-15% of the depth of
filter medium; Polarization of gel-forms, etc.

All filtration is 'particle specific' .... and depends exactly which
mechanism of capture 'predominates' for which type of particle you want
to remove. For fuel oil, etc. filtration where probably there are more
'deformable' particles or particles that can change shape under
increasing differential pressure and then are subject to extrusion
either through or partly through the media (settling deeper into the
media) thus 'blinding it' ..... vacuum filtration has historically
shown the least efficacy of on-stream service life versus pressure
filtration. Apparently vacuum feed filtration allows the deformables
and smaller than 'seiving' size particles to partly extrude more deeply
into the matrix, partly closees off the statistical pores which
increases the face velocity of the fluid in the cross sections of the
filter matrix. The increasing face velocity of the fluid through the
sections creates an untowards physical event (as per the standard
D'Arcys equation) derived to be: On stream life (T1/T2) being a
function of the ratio of face velocities to the 'n-th' power where 'n'
- approximately approaches to the 2/3 power). My 'guess' (after 35
years of observation, etc.) is that in vacuum filtration the capture
involves an *accelerating* particle; while pressure feed involves a
*decelerating* particle.

Simplistically and historically, vacuum draws the deformables and
smaller than the target 'seiving sized' particles deeper into the
matrix, shuts down the open flow paths quicker than in pressure feed
--- all apparently internal velocity dependent.
Filtration hydrodynamics is probably very similar to aerodynamics where
intuition and simple logic will always produce the wrong answer. I've
been deeply involved in ultra-purity filtration and 'separations'
engineering (and the physical chemistry of) for almost 35 years and
still dont know all the answers .... although I do know that vacuum
feed filtration will *always* have comparatively shorter service life
than pressure feed (for just about ALL filtrations) ... and for that
reason alone is good enough for me and most others to stay away from
vacuum feed filtration. There's probably a doctoral discertation
waiting for someone who can correctly figure this one out - many have
tried but none have ever been successful.

Like I posted earlier, filtration has nothing to do with 'screen doors'
and is an extremely variable complex entity at below the macroscopic
level. Dont attempt to 'rationalize' it as you will ultimately always
wind up with the wrong solution. It's really an 'art-form'.

Not to mention that vacuum filtration is intrinsically less robust from
a purely mechanical perspective. Under vacuum filtration, you have, at
most, atmospheric pressure and tank head pressure available to generate
filter DP (which, even with 10' of head - very unlikely in a boat -
amounts to 20psi). Under pressure filtration, you're limited only by
pump size/flow curve, and filter specifications. If you have a filter
rated for 65psid, why would you want to toss it when the DP is 15psi (at
which point the resulting flow rate, using vacuum, would likely be
negligible)?

Vacuum filtration, using any realistic type of circulation pump, results
in a low discharge pressure (i.e. open tank return line) and very low
suction pressure (increasing with filter load), which is a recipe for
cavitation and low/no flow conditions. Pressure filtration, on the
other hand, maintains pressure (typical installation with sufficient
head on the pump) on the suction side, and a higher discharge pressure
(increasing with filter load). Thus filter loading decreases the
chances of pump cavitation for pressure filtration, versus increasing
chances under vacuum filtration.

So, whether you agree with Rich's observations or not, there are sound
hydraulic reasons for pressure filtration instead of vacuum filtration.

Keith Hughes

Rich Hampel wrote:
I
Retention of particulate in/on a filter is an extremely complex entity
due to simultaneous and varied 'capture mechanisms'. that 'hold' the
particles in place: seiving - where the statistical pores of the filter
structure are smaller than the particle; inertial impaction - where the
particles leave the flow stream when the flow stream takes sharp bends;
aDsorption - where the particles are held to the filter media subtrate
by weak electronic bonding (van der waals forces); the formation of a
"cake" on the upper surface and into the upper 10-15% of the depth of
filter medium; Polarization of gel-forms, etc.

All filtration is 'particle specific' .... and depends exactly which
mechanism of capture 'predominates' for which type of particle you want
to remove. For fuel oil, etc. filtration where probably there are more
'deformable' particles or particles that can change shape under
increasing differential pressure and then are subject to extrusion
either through or partly through the media (settling deeper into the
media) thus 'blinding it' ..... vacuum filtration has historically
shown the least efficacy of on-stream service life versus pressure
filtration. Apparently vacuum feed filtration allows the deformables
and smaller than 'seiving' size particles to partly extrude more deeply
into the matrix, partly closees off the statistical pores which
increases the face velocity of the fluid in the cross sections of the
filter matrix. The increasing face velocity of the fluid through the
sections creates an untowards physical event (as per the standard
D'Arcys equation) derived to be: On stream life (T1/T2) being a
function of the ratio of face velocities to the 'n-th' power where 'n'
- approximately approaches to the 2/3 power). My 'guess' (after 35
years of observation, etc.) is that in vacuum filtration the capture
involves an *accelerating* particle; while pressure feed involves a
*decelerating* particle.

Simplistically and historically, vacuum draws the deformables and
smaller than the target 'seiving sized' particles deeper into the
matrix, shuts down the open flow paths quicker than in pressure feed
--- all apparently internal velocity dependent.
Filtration hydrodynamics is probably very similar to aerodynamics where
intuition and simple logic will always produce the wrong answer. I've
been deeply involved in ultra-purity filtration and 'separations'
engineering (and the physical chemistry of) for almost 35 years and
still dont know all the answers .... although I do know that vacuum
feed filtration will *always* have comparatively shorter service life
than pressure feed (for just about ALL filtrations) ... and for that
reason alone is good enough for me and most others to stay away from
vacuum feed filtration. There's probably a doctoral discertation
waiting for someone who can correctly figure this one out - many have
tried but none have ever been successful.

Like I posted earlier, filtration has nothing to do with 'screen doors'
and is an extremely variable complex entity at below the macroscopic
level. Dont attempt to 'rationalize' it as you will ultimately always
wind up with the wrong solution. It's really an 'art-form'.