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

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

On Thu, 08 Jan 2004 14:53:44 GMT, Rick wrote:

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 all depends on how many "all" is, the max pressure differential you
want to operate at and how much vacuum the pump can draw. 2 stages
should be fine. 3, probably not.

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.

I have 3 stages with an electric pump between the 2nd and 3rd and then
the engine lift pump after the 3rd. Works pretty good. The only time
it stopped working, leading me to thinking there was a vacuum leak, was
when the tank vent clogged and vacuum built up in the tank to the point
where fuel couldn't be drawn out anymore. Problem solved temporarily by
opening the filler.

Steve

On Thu, 08 Jan 2004 14:53:44 GMT, Rick wrote:

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 all depends on how many "all" is, the max pressure differential you
want to operate at and how much vacuum the pump can draw. 2 stages
should be fine. 3, probably not.

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.

I have 3 stages with an electric pump between the 2nd and 3rd and then
the engine lift pump after the 3rd. Works pretty good. The only time
it stopped working, leading me to thinking there was a vacuum leak, was
when the tank vent clogged and vacuum built up in the tank to the point
where fuel couldn't be drawn out anymore. Problem solved temporarily by
opening the filler.

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