One of the most common problems with diesel powered boats is gunk in the
fuel.... this is a fault of diesel's virtue of being so economical that
fuel sits around for a long time getting gunked up... gasoline engines
suck up their fuel too fast for this to happen

Anyway our boat had a RACOR 900FG filter when we bought it, installed in
a not-too-great location on the aft bulkhead of the engine room. It was
accessible, but only by climbing over the engine. Not a good scenario
for clearing a filter underway. Also, there was no way to install a
parallel filter for easy switching. No vacuum gage.

I also talked to a lot of diesel experts about the filter size. This is
a 90 gallon per hour filter, and our engine pulls in about 7 or 8 gph
max (it does not recirc much fuel). This means that the turbine water
seperator was not getting enough flow to spin the fuel, no centrifuge
effect. The extra large bowl might help water settle out, but never
showed any water.

So I am doing a couple of things
1- replacing the R-900FG with a 500/75 twin filter, rated at 60 gph in a
parallel mount with a vacuum gage. We are planning to use 2 micron
filter elements.

2- increasing the suction piping to 1/2" OD tubing.

3- installing the new filter assembly right below an access door cut in
the aft ladderway, so that the filters can be reached without entering
the engineroom much less climbing over the engine itself.

4- installing suction & supply manifolds so that either tank can be
selected and any of the diesel fueled equipment (engine, genset, heater)
can be cut in or out of the fuel loop.

5- provision for a polishing pump to be installed at a later date. One
of the tidbits I learned was the a polishing pump discharge should NOT
be piped into the engine recirc line. Backpressure to the injector pump
(even a tiny bit) is bad. So bad that a check valve is not going to do
the job. This may be different on different engines.

Right now the job is about 3/4 done and I have all the tools and parts
to finish it up... makes me nervous to have the fuel system
disassembled. So maybe this coming weekend we will be able to get
underway again!

Fair Skies
Doug King

On Tue, 17 Feb 2004 13:32:47 -0500, DSK wrote:
One of the most common problems with diesel powered boats is gunk in the
fuel.... this is a fault of diesel's virtue of being so economical that
fuel sits around for a long time getting gunked up... gasoline engines
suck up their fuel too fast for this to happen

Anyway our boat had a RACOR 900FG filter when we bought it, installed in
a not-too-great location on the aft bulkhead of the engine room. It was
accessible, but only by climbing over the engine. Not a good scenario
for clearing a filter underway. Also, there was no way to install a
parallel filter for easy switching. No vacuum gage.

I also talked to a lot of diesel experts about the filter size. This is
a 90 gallon per hour filter, and our engine pulls in about 7 or 8 gph
max (it does not recirc much fuel). This means that the turbine water
seperator was not getting enough flow to spin the fuel, no centrifuge
effect. The extra large bowl might help water settle out, but never
showed any water.

So I am doing a couple of things
1- replacing the R-900FG with a 500/75 twin filter, rated at 60 gph in a
parallel mount with a vacuum gage. We are planning to use 2 micron
filter elements.

2- increasing the suction piping to 1/2" OD tubing.

3- installing the new filter assembly right below an access door cut in
the aft ladderway, so that the filters can be reached without entering
the engineroom much less climbing over the engine itself.

4- installing suction & supply manifolds so that either tank can be
selected and any of the diesel fueled equipment (engine, genset, heater)
can be cut in or out of the fuel loop.

5- provision for a polishing pump to be installed at a later date. One
of the tidbits I learned was the a polishing pump discharge should NOT
be piped into the engine recirc line. Backpressure to the injector pump
(even a tiny bit) is bad. So bad that a check valve is not going to do
the job. This may be different on different engines.

Right now the job is about 3/4 done and I have all the tools and parts
to finish it up... makes me nervous to have the fuel system
disassembled. So maybe this coming weekend we will be able to get
underway again!
============================================
One cautionary note. Before you increase the size of your fuel intake
tubing to 1/2 inch, be sure that your fuel pumps are up to the job. I
had an issue several years ago with recurring fuel pump failures on my
generator. It turned out that the dealer had used 3/8 fuel hose to
the genset instead of the recommended 1/4 inch and that was enough
extra load to cause premature failure (it was pumping from a 320
gallon tank).

Wayne.B wrote:
One cautionary note. Before you increase the size of your fuel intake
tubing to 1/2 inch, be sure that your fuel pumps are up to the job. I
had an issue several years ago with recurring fuel pump failures on my
generator. It turned out that the dealer had used 3/8 fuel hose to
the genset instead of the recommended 1/4 inch and that was enough
extra load to cause premature failure (it was pumping from a 320
gallon tank).


???

If the fuel pump is a positive displacement (which AFAIK they all are)
and the fuel flow is regulated (which it will be, by the injector pump),
then increasing the size of the piping will *reduce* the load on the pump.

I wonder if your problem was with the pressure regulator?

Fair Skies
Doug King

On Wed, 18 Feb 2004 12:24:44 -0500, DSK wrote:

If the fuel pump is a positive displacement (which AFAIK they all are)
and the fuel flow is regulated (which it will be, by the injector pump),
then increasing the size of the piping will *reduce* the load on the pump.

===========================================

The fuel pump on my generator is a small electric unit. I don't know
if it is positive displacement ot not but reducing the supply diameter
fixed the problem for sure.

Is it not true, that in "lift" mode, the pump is lifting less weight
of fuel in a small diameter line?

"Wayne.B" wrote:


The fuel pump on my generator is a small electric unit. I don't know
if it is positive displacement ot not but reducing the supply diameter
fixed the problem for sure.

Is it not true, that in "lift" mode, the pump is lifting less weight
of fuel in a small diameter line?

If the volume per unit of time is the same, then the amount of work output is
the same. It would be lifting more fuel at any given instant, but lifting it
slower. The differential pressure across the pump would be less... this is what
I usually think of as 'load' on a pump. If for some reason, your fuel system
was designed around a given flow at a given differential pressure, then
changing sizes could indeed screw it up.

But the raw physcs doesn't explain everything. Thank you for the cautionary
note... sometimes machinery can act very oddly. One might almost swear it's...
alive!

Fair Skies
Doug King