Pull the fuel through the filter, don't push.

"Doug Dotson" wrote in message
...
I am assembling my posihing system. Not clear whether it is better
to put the pump on the pressure side or the vacuum side. Having no
filter on the intake of the pump seems risky. I am using a 2 stage
approach. maybe putting the filter between the filters is an option.

Doug
s/v Callista

"R" == Rick writes:

R 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.

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


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


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


R Rick

Do you happen to know if there is any centrifugal separator on the
market suited to small boats? I cannot really think of any technical
reasons why not, but perhaps the market isn't there. Btw., I once had
a Scania truck diesel engine which had a centrifuge for its
lubrication oil. Judging from the amount of gunk it separated out of
the oil, it worked very well.

--
This page intentionally left blank

"R" == Rick writes:

R 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.

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


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


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


R Rick

Do you happen to know if there is any centrifugal separator on the
market suited to small boats? I cannot really think of any technical
reasons why not, but perhaps the market isn't there. Btw., I once had
a Scania truck diesel engine which had a centrifuge for its
lubrication oil. Judging from the amount of gunk it separated out of
the oil, it worked very well.

--
This page intentionally left blank

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

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

Rick wrote:

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.

Then it sounds like it would be better to have the pump past the filters.

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.

Well, now I have to ask why the pump should be before the finer stages
of filtration. It seems to me that as long as it can maintain a
sufficient pressure differential across all the stages of filtration, it
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.

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

I do, but it's a little big to fit on the boat.

Steve

Rick wrote:

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.

Then it sounds like it would be better to have the pump past the filters.

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.

Well, now I have to ask why the pump should be before the finer stages
of filtration. It seems to me that as long as it can maintain a
sufficient pressure differential across all the stages of filtration, it
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.

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

I do, but it's a little big to fit on the boat.

Steve

David Flew wrote:

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.

Personally, I'd rather diagnose a leak in a vacuum system that stops the
engine due to air getting in the system than one in a pressure system
that keeps running but pumps fuel into the bilge until your tanks are
dry and then stops the engine. But that's just me.

Steve

David Flew wrote:

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.

Personally, I'd rather diagnose a leak in a vacuum system that stops the
engine due to air getting in the system than one in a pressure system
that keeps running but pumps fuel into the bilge until your tanks are
dry and then stops the engine. But that's just me.

Steve

After 30 years of screwing around with this stuff I cant still give a
an accurate technical reason .... my 'opinion' is the 'regime' of
particle depositionIn and the formation of 'filter cake' ..... on a
pressure filtration the deposition begins mostly on the upper surface
or at least within 5% depth of the surface, while with vacuum
filtration the deposition is essentially INSIDE the matrix of the
media. Being inside the matrix causes higher internal velocities
which drive the particles deeper and deeper into the matrix ... causing
an exponential decrease in service life. ..... its the same for depth
as well as membrane filtration.
The quandy is that the fluids are incompressible and shouldnt make any
difference due to the direction of motive pressure .... but in practice
it does, it always does.


article , Steven Shelikoff
wrote:

On Thu, 08 Jan 2004 02:51:46 GMT, Rich Hampel
wrote:

NOPE!
In pressure mode, the filter will also act as a 'coalescer' (bringing
similar surface tension fluids together to make larger and larger sized
particles) and such particles will settle out into a 'drop-out-pot'
..... or usually into the bottom of the filter bowl (bowl pointing
downwards). The smaller the retention size of the filter media the
more efficient the coalescing efficiency.
On the very bottom of the filter bowl, add a pigtail of oil compatible
transluscent plastic tube (Tygon, etc.) with a cock on the end ....
when you see water in the pigtail simply drain the bowl. Thats the
same way a racor with an integral clear plastic knock-out-pot works.

If you are regularly polishing the fuel the coalesced emulsions will be
removed/trapped in the inverted filter bowl .... that why you put the
dip tube for the recirc system at the VERY bottom of the tank and a
drain cock on the inverted filter bowl.

Dont want air leaks or fuel oil leaks ------ dont use compression
fittings, use flared or better fittings.

Pump should have a SCREEN (preferably integral) for protection to
prevent damage by *huge* particles that would tear the rubber impeller
or wobble plate.

I say again, if you want long service life and efficient filtration
employ PRESSURE filtration, especially on a recirculation system.

The ONLY reason I can think of why fuel systems in boats use vacuum
filtration is ........... the engine manufactures supply the lift pump
and 'guard' filter - and puts it on the engine ...... and not on the
tank (where it SHOULD BE). Cheap and dirty solution, easier for the
boat builder - less wiring, less design, less effort, ....

All this begs the question, why does the filter media care whether it's
in "pressure" mode or "vacuum" mode? Sure, the plumbing and filter
cases care. But the media only sees a pressure differential across it.
What's the difference to the media if the there is 14psi (atmospheric
pressure) on one side and, say, 10 psi (a 4 psi vacuum drawing fuel
across the media) on the other side vs. 18 psi (4 psi pressure pushing
fuel across the media) on one side and 14 psi (atmospheric) on the
other?

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.

Steve