On Thu, 23 Nov 2006 19:47:23 GMT, Rich Hampel
wrote:

Recirculation filters should be set up as PRESSURE FEED not vacuum feed
where the pump is at the END of the circuit ..... the filters will be
vastly more efficient versus on-stream service life due to the better
deposition of particles ON the filter surface than IN the filter when
in vacuum feed mode. The Walbro has an integral screen of about

When the filter media sees a pressure differential, how does it know
whether it's caused by sucking on one side or pushing on the other?
Does the filter media actually get compressed by the slightly (tiny)
higher pressure inside the filter housing when it's in pressure feed
vs. vacuum feed? Since the fibers are surrounded by the fluid, the
pressure on each fiber is pretty much equal all around. The only
difference being the difference between the front of the fiber and the
back, which only depends on the differential not the absolute
pressure. So the only way I can see pressure vs. vacuum makin a
difference is if the actual fibers get compressed and get smaller in
diameter by the higher pressure in the canister. But now I have to
understand how only a few PSI difference can cause any significant
deformation/compression of the media fibers.

The only other thing I can think of is maybe the fluid flow rate is
faster for pressure fed vs. vacuum because the pump may be operating
more efficiently that way. But then, assuming the flow rate is
different, the opposite situation would occur. I.e., particles would
be deposited IN the filter for the faster flow rate (pressure) vs. ON
the surface for the slower flow rate (vacuum)

Anyway, enough of my rambling. I'd just like to understand why
particles get deposited ON the filter surface for pressure fed and IN
the filter for vacuum fed.

Steve