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

Steven Shelikoff wrote:

Well, now I have to ask why the pump should be before the finer stages
of filtration.

Because you can install canned filters which are rated for
high pressure downstream of the pump, on the pressure side.
The filters on the suction side are fairly coarse, produce
little resistance to flow until clogged, and can perform the
initial separation of water and solids.

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.

If the pump was upstream of all filters, so that it sucked
through them all, the differential available is pretty low.
That is why most installations use Racors on the suction
side for the reasons I have given and then the final filters
are can filters on the pressure side.

We seem to have gotten away from the polishing thread here
but there really isn't much difference.

One thing to keep in mind, this process is not designed to
conserve on filters, it is supposed to clean fuel.

Rick

Steven Shelikoff wrote:

Well, now I have to ask why the pump should be before the finer stages
of filtration.

Because you can install canned filters which are rated for
high pressure downstream of the pump, on the pressure side.
The filters on the suction side are fairly coarse, produce
little resistance to flow until clogged, and can perform the
initial separation of water and solids.

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.

If the pump was upstream of all filters, so that it sucked
through them all, the differential available is pretty low.
That is why most installations use Racors on the suction
side for the reasons I have given and then the final filters
are can filters on the pressure side.

We seem to have gotten away from the polishing thread here
but there really isn't much difference.

One thing to keep in mind, this process is not designed to
conserve on filters, it is supposed to clean fuel.

Rick

Ole-Hjalmar Kristensen wrote:

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.

Alfa Laval makes a cute little unit that will process about
170 liters/hour. Alfa sells it mounted on a cart with pump
and controls for use as a portable oil polishing unit. The
centrifuge is available by itself.

I would love to have one but the cost is a bit too high to
justify its use on a pleasure boat.

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.

A "spinner" that worked off the oil itself? Those things are
great. Have used them on several diesel generator sets and
they do an excellent job. A little trick to make them easier
to clean, line the bowl with a single layer of newspaper.

Rick

Ole-Hjalmar Kristensen wrote:

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.

Alfa Laval makes a cute little unit that will process about
170 liters/hour. Alfa sells it mounted on a cart with pump
and controls for use as a portable oil polishing unit. The
centrifuge is available by itself.

I would love to have one but the cost is a bit too high to
justify its use on a pleasure boat.

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.

A "spinner" that worked off the oil itself? Those things are
great. Have used them on several diesel generator sets and
they do an excellent job. A little trick to make them easier
to clean, line the bowl with a single layer of newspaper.

Rick

"R" == Rick writes:

R Ole-Hjalmar Kristensen wrote:
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.

R Alfa Laval makes a cute little unit that will process about 170
R liters/hour. Alfa sells it mounted on a cart with pump and controls
R for use as a portable oil polishing unit. The centrifuge is available
R by itself.

Interesting.

R I would love to have one but the cost is a bit too high to justify its
R use on a pleasure boat.

Yes, you're probably right, unless you could share it with others,
being a portable unit.
I was thinking of a small unit which could be permanently attached to
the fuel system and used either for polishing or for processing the
fuel when filling a day tank.

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.

R A "spinner" that worked off the oil itself? Those things are
R great. Have used them on several diesel generator sets and they do an
R excellent job. A little trick to make them easier to clean, line the
R bowl with a single layer of newspaper.

Yes, it used the oil pressure to spin the bowl, and you had to
manually clean the inside of the bowl. The newspaper trick would have
been great, but I did not think of it 25 years ago...

R Rick


--
This page intentionally left blank

"R" == Rick writes:

R Ole-Hjalmar Kristensen wrote:
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.

R Alfa Laval makes a cute little unit that will process about 170
R liters/hour. Alfa sells it mounted on a cart with pump and controls
R for use as a portable oil polishing unit. The centrifuge is available
R by itself.

Interesting.

R I would love to have one but the cost is a bit too high to justify its
R use on a pleasure boat.

Yes, you're probably right, unless you could share it with others,
being a portable unit.
I was thinking of a small unit which could be permanently attached to
the fuel system and used either for polishing or for processing the
fuel when filling a day tank.

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.

R A "spinner" that worked off the oil itself? Those things are
R great. Have used them on several diesel generator sets and they do an
R excellent job. A little trick to make them easier to clean, line the
R bowl with a single layer of newspaper.

Yes, it used the oil pressure to spin the bowl, and you had to
manually clean the inside of the bowl. The newspaper trick would have
been great, but I did not think of it 25 years ago...

R Rick


--
This page intentionally left blank

Why?

Doug
s/v Callista

"Keith" wrote in message
...
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

Why?

Doug
s/v Callista

"Keith" wrote in message
...
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

I think I'll put the pump between the filters. 10 micron on
the vacuum side, 1 micron on the pressure side.

Doug
s/v Callista

"Rich Hampel" wrote in message
...
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