On Sun, 07 Dec 2003 06:24:24 GMT, Rich Hampel
wrote:

Nope.... I suggest a test for you
Take 25-50 grams of the finest dust/crud you can find. Dump it in
upstream of a TP filter and see what happens ..... it will immediately
plug - or will hardly capture anything.

OK; as far as I can tell, particulate fines *will* pass a depth filter
on the first pass. This makes your proposition completely true for one
clause of the either/or proposition.


Change to a high surface area pleated filter dump in 25-50 grams of
crud, another 25-50 grams of crud, another 25-50 grams, then another
25-50 grams, then another .... then it will plug.

OK: as far as I can tell, particulate fines will mostly pass a surface
filter rated for considerably larger particles, and block, for a
filter rated at considerably smaller particles. In the intermediate
range, as is well known, the retained particulate film provides
increasing resistance, and retention of decreasing particle sizes.

Take out the
filter, examine .... you will find a small layer of crud on the
surface. That layer is called a "filter cake". That layer of debris
because the velocity throuth the 'cake' is so much smaller (than the
velocity through a TP etc. roll

This was the only piece that left me uncomfortable. Supposing that
surface filters use lower velocity flow than depth filters in the
fuel polishing role is presuming a design choice that "don't
necessarily happen." Filter cakes are an artifact of surface
filters.

....that it does in fact flow and until the
cake reaches a 'terminal' differential pressure will be the principal
means of particle captu dirt filtering out other dirt.
This cannot happen in a depth filter....because there is *no room for
the 'cake' to form* (inside the filter).

For a true depth filter, you add a filter aid (Diotomaceous earth,
perlite, etc.) on a continual basis so that the deposition is
controlled, the debris is contained in the cake of DE + crud.

I am pleased that you are now referring to industrial uses of depth
filters: - like the one that brings you your tap-water, for instance,
or the depth filter that brings you your room-air.
But pre-loading a filter is not the fuel-polishing approach, so I
don't find it specially relevant,

The
surface of the depth filter holds the cake. If the particles get
inside the depth filter it PLUGS. You can design a 'profiled' depth
filter that has a graded pore density.... bigger pores on the upstream
side, smaller pores on the downstream side ....and that costs about 20
times the price of a toilet paper roll ..... and also is a resin bonded
cellulose matrix. Resin bonded so that the cellulose matrix desnt
collapse upon itself during increasing differential pressure, doesnt
fall apart if it gets wet with water, etc.

You again mention non resin cellulose filters falling apart when wet.
The home test I mentioned recently (I thought) would convince you
that these filter materials *don't get wet* in the intended
application?

Brian W




In article , Brian Whatcott
wrote:

On Fri, 05 Dec 2003 20:02:22 GMT, Rich Hampel
wrote:

Please appreciate that I dont want to appear to be an arrogant
know-it-all after being in on and around critical filtration/separation
most of my working life ...

Sounds good to me...

/// Whats wrong with TP, etc. is that the material used to filter
is not bonded, can digest (make more particles) in the presence of
water --- thus to do the exact opposite of what you are trying to do.

Perhaps a test at home would be helpful.

Take a kitchen collender, A seive or funnel would also work well.
Place a sheet of kitchen roll in the aperture, pleated once to fit.
Spray the surface with Pam, olive oil, or soybean oil or any other oil
Momma has on hand. Make sure the paper is saturated.

Now pour water onto the surface.
Let me know how many particles break loose.
We'll compare notes if you like...
///
My objection to TP - very poor efficiency, migrates particles, migrates
fibers
\////
You either believe the folks who say that depth filters have saved
their fine surface filters from blocking, or you don't.
If you do believe that they are reporting honestly, then I imagine
you would say that at the operational level, that's the kind of
efficiency they prefer?

The home test may (or may not) demonstrate that an oil-soaked paper
tissue does not migrate particles or fibers.
I expect you will let us know if this is misconceived...

DO NOT depend on filters to remove the crud in your system.
////

Or in the version I prefer, referring only to the surface filters that
you use and prefer:
DO NOT depend on fine surface filters to remove crud in your system -
they will certainly block: fast.

Respectfully,

Brian Whatcott