Its the way that the deposition of debris in a filter behaves, if you
build the 'cake' inside the filter media the life of the filter becomes
very short in comparison to 'cake' formation on or 'immediately inside'
the surface.
There is a valid doctoral discertation awating the person who solves
this dilemma ... so far no one can fully explain it, and the filtration
industry will stand pat on pressure filtration vs. vacuum filtration
.... all based on actual performance data.



In article , Steven Shelikoff
wrote:

On Fri, 09 Jan 2004 00:59:52 GMT, Brian Whatcott
wrote:

On Thu, 08 Jan 2004 05:54:34 GMT, (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). ///

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


Looks like the contribution that mentioned a pressure pump's tendency
to mix and chop big water drops to a clogging emulsion where the
vacuum pump sucks them into the filter intact - that idea didn't
appeal to you?

Sure did. So does the idea that I'd rather have a malfunction that lets
air into the system than one that lets fuel out. But both of those
points leads to the conclusion that you should suck fuel through the
filter rather than push it through.

However, Rich recommends that fuel be pushed through due to some
tendency of the filter media to work better in that mode. Thus my
question, discounting all other aspects at hand such as the pump
emulsifying the fuel before it gets to the filter, why does the filter
media care which side the pump is on? Fuel is being pushed through it
either way, either by the pump with a higher pressure on the inlet or
the atmosphere with a higher pressure on the inlet.

Steve