T&T: Installing an electric fuel pump for priming .....

[Candy Chapman and Gary Bell]

Captain Mike,

You said:
If you want to use your electric fuel pump as a filter then install it
before your racor. If it plugs up; your engine will come to a halt and
it might be said that you will deserve whatever happens to you.

and I reply:
In your first and third paragraph you make your point that putting the pump
first is inappropriate because the pump is the filter.  I think that what you
meant is that you prefer to have the filter first to guard the pump from
ingesting something it cannot pass.

My point in my earlier message was that pumps of every sort can manage healthy
flows with a load on the output far better than one with a substantial load on
the input.  I understand about your point of using the filter to protect both
the engine and the pump.  I suggest that the pump doesn't need to be protected
from a few micron sized particles, which is what the filter does best.  The
pump does need to be protected from the 'glob of gunk,' and a Racor will do
that.  Very likely the filter will not pass very many of these globs, but a
filter in the inlet side of a pump will provide lots more load (pressure drop)
than an adequate screen.  A pump after the filter will not allow bleeding the
filter.

Mike again:
I had a boat last fall that had just such an installation with a cheap
Napa fuel filter before the pump. The little filter would plug up every
few minutes and the engine would stop. Since we did not have many of
these spare filters, I had to reverse purge them and reinstall in order
to get the engine running. This was on a single screw boat.

And Gary:
Here is where I get confused.  You use this as an example of the folly of
putting the pump first.  Then you describe in detail the trouble you had with
a small filter before the pump.  I originally suggested a strainer, not a
filter which would block a chunk large enough to choke the pump, and to let
the later Racor take care of removing the tiny stuff that we want to block
from getting to the engines.  If there is so much of that tiny gunk that the
filters are not able to cope, you are already in deep doo-doo, and if the
maneuvering situation was dire enough I might even consider feeding cruddy
fuel to the engine and trading off expensive engine damage against surviving
the maneuvering crisis.

Here's an idea:  A delivery skipper might be able to bring a five gallon fuel
container of freshly cleaned fuel fitted with a long hose (for good gravity
feeding) and a couple of valves and fittings to allow inserting it as an
emergency backup.  Tap it into the fuel system between the filters and the
lift pump, place the container high enough to provide gravity feed, and
standby to turn it on when the chips are down.

And Mike in closing:
Putting the pump before the racor simply means that the pump is now in
effect, the FILTER. It is only a matter of time before a glob of gunk
brings the whole show to a halt.

Do it any way you want, but when the engine stops you can't complain
that you weren't warned.

Gary:
We are already intimidated by the risks of contaminated fuel shutting down our
power plants at the very worst time, when the water gets bouncy.  That is what
motivates all of us to improve our fuel filtering systems, and this discussion
thread.  I am not yet convinced that the placing the main filters before the
pump will resolve any contamination problems.  I suggest that where the pump
came first in a system, if there was a strainer on the pump inlet (where the
little Napa filter was in your example) you might have been able to manually
clean the screen, and  if the little filter was not present, the amount of
gunk in the system would not have shut down a fuel pump but instead would have
taxed your supply of Racor filters regardless of whether the pump or the
filter was first.  It may have been the case that the gunk was adequate to
cripple the pump, or perhaps not, but it absolutely should not have gotten
close to the engine!  I sympathize deeply with the difficulty your example
illustrates, that fuel systems can present horrible levels of gunk that were
not evident until the tank got bounced around, and then the situation was
particularly inconvenient or downright dangerous.

The listees discussing this issue are sure to be more conscientious about
their fuel systems than the folks who hire delivery skippers, as a rule.  We
are less likely to have large accumulations of gunk, and as a result of our
discussion and preparations, will be better able to deal with it.

Best of luck
Gary Bell

My earlier posting about putting a small to moderate 'day tank' between a
large polishing type filter and the engine lift pump, would allow the engine
to run for some predictable time even after the polishing filter system packed
it it altogether.  That day tank would emphatically not be a fuel storage
tank, meaning that it would drain its contents back to the storage tank after
use, and no gunk would ever grow in it.

Clearly it is best to discover any gunk problems before starting your journey,
or provide an effective polishing outfit.  If the fuel storage tanks can be
guaranteed to be free of filter plugging gunk by routine polishing that would
be great, but given that few boats have routine polishing systems in place,
that remains a goal.  If we could inspect the entire tankeage system for crud
before using the boat, like taking avgas samples from the low points on every
tank during preflight, that would most likely make fuel starvation from
contaminated fuel a non-issue too.  I can't think of a practical way to
retrofit our boats with sampling sumps; and clearly not every boat a delivery
skipper might ever encounter will have a working fuel polishing rig.

Regards,
Mike


_____________________________________
Capt. Mike Maurice
Beaverton Oregon(Near Portland)