"DSK" wrote in message
.. .
jps wrote:
Doug, if the first filter is responsible for both large and small
particles, isn't it going to clog more quickly?


Nope. If the amount of gunk in the fuel is the same, then the filter(s)
will pick it up in pretty much the same time, given the same fuel flow
rate (within the limits of random distribution).



The point is that you're distributing the gunk across a larger surface
area by doing it in series.


Which accomplishes what? I've heard it said that there will be less
pressure drop, which I don't think is true. Two partially clogged filters
equals two lesser pressure drops, but if the flow is equal and the
restriction is equal, then is the pressure drop... what, not equal? And if
the filters are sized for the flow your engine needs, then the pressure
drop will not be large enough to cause a problem.



For example I use a Racor 45gph filter (which is very much more flow than
my engine will ever use) with 2 micron elements in in, as a primary. It
will seperate water and trap everything I want to keep out of the engine.
Changing the element is much easier than rebuildin the injector pump. It
is rated at 45gph whether you put in the 30, 20, 10, or 2 micron element.

Obviously the 2 micron element will clog quicker, but that's what you
*want* it to do: keep that gunk out of the engine. And why put in a 30
then a 2 and have to change them both?


Because it'll take twice as long to clog?


Don't think so. They'll both clog in approximately the same amount of
time... if the same amount of gunk is trapped in them.

And even if they *do* take twice as long to clog, what have you gained?
You have to have two pairs of parallel filters or shut down, and change
two filters, and carry two different sizes of filter on board.



If you really want to set up your system to not have to change fuel
filter elements, then just don't have one at all and rebuild your
injection system annually. Wouldn't that be easier & cheaper??


You've assumed he's a diesel user, but when someone uses the phrase "gas
tank" I assume it's gas.

We're assuming different kettles of fish.


Not if it's a fuel injected gas engine. If it's carburetted, then a filter
is not anywhere near as important, just a water seperator.

DSK

If the tank is really bad, have it cleaned and checked to see if the tank is
even safe. Especially gas. Or if just crud, make a day tank. Lots of
older diesel fishing boats use this method. a second small tank that can be
easily cleaned, and the first tank pumps fuel into the aux tank and then the
engine feeds off the aux tank. Is designed so the crud will settle in the
aux / day tank.
jps

Calif Bill wrote:
If the tank is really bad, have it cleaned and checked to see if the tank is
even safe. Especially gas. Or if just crud, make a day tank. Lots of
older diesel fishing boats use this method. a second small tank that can be
easily cleaned, and the first tank pumps fuel into the aux tank and then the
engine feeds off the aux tank. Is designed so the crud will settle in the
aux / day tank.


That's a very good solution (pardon the pun) to the
problem... it does take up a bit of extra room though. If
you're cruising and buying fuel in a lot of faraway places,
having an on-board polisher & a day tank is the only way to
keep the power plant reliable.

Fair Skies
Doug King