Filters

[pbknowles]

As a supplement to all the recent discussion on filtration, I would like to offer the following:
Fluid filters are classified as Absolute and Nominal. Absolute filters have had their Beta ratio (more on that later), dirt holding capacity and efficiency measured and classified by standardized testing following the guidelines of ISO (International Standards Organization) NAS (National Aerospace Standards). Nominal filters are rated by the manufacturer, without reference to any recognized standard. Basically they can rate them any way they want as long as they don’t reference a recognized standard. Nominal filters are usually constructed of pleated paper or cellulose material. Automotive type oil filters fall into the nominal category.

*Special note about reverse flow through automotive oil filters: The element is designed to be collapse resistant in only one direction. As soon as some delta pressure is generated in the reverse flow direction the unsupported pleated paper will just rupture.

Absolute filters are constructed of fiberglass or other inorganic materials and are usually a “depth” filter; that is the filter media has depth, with gradually decreasing space between the fibers as the fluid passes through. The point of this is to show that a 10 micron filter element installed in a system does NOT mean that all particles greater than 10 micron are removed. All 10 micron elements are not created equal, and even the best of them will not remove all the 10 micron and larger particles. Why? The Beta ratio provides the answer:

Beta ratio = Number of particles of a given size upstream of the filter/number downstream. For example, Beta ratio = 1000/10 = 100, or put another way, 1% of the particles will get through the filter. The other element of Beta ratio is the particle size. You will see it expressed this way: B10>100 which means the filter will allow no more than one 10 micron particle downstream for every 100 upstream.

In summary, depth type filters with decent Beta ratios are expensive, with a typical element the size of an automotive oil filter element costing upwards of $35. Probably too pricey for a grass roots biodiesel project. Nominal filters are cheap and available, but do not be fooled into thinking that they are 100% efficient. 30-40% is probably more like it. High delta pressures across the element can cause them to collapse, and also causes particles to be forced through the filter media. Pulsating flow has the same effect. Some of their limitations can be overcome by running them in series, and they are probably good enough. Keep this info in mind however when we hear reports of engine component damage from "filtered" fuel. Of course, none of the above mentioned filters will remove water or organics either.

[01stroker]

Very interesting reading! Thanks.

[h2odrx]

oh wise one, where does this knowledge come from? and does this work for all filters? like say the type some sell as whole house filters?
thank you for your reply!

[pbknowles]

Parker has a pretty good read on filters here: http://www.parker.com/hydraulicfilter/cat/HTM-3004.pdf
Fram has a write up here:
http://www.fram.com/pdf/FluidFilterRating.pdf
I work with aerospace hydraulics and we naturally get pretty excited about keeping our systems clean. To filter my WVO I use a 100 micron suction strainer before the pump followed by two whole house type filters in series, a coarse pleated paper one followed by a finer one of the type that looks like a spool of threads wound in a crosshatch pattern. It is my belief that this filter functions like the "depth" variety, but the mfr. makes no claims about actual filter performance. All of this is followed by the stock secondary filter for my Isuzu engine. After the holidays I am going to draw a sample of the WVO and have the materials lab where I work perform a particle count analysis to determine how well the filters are working. If there is any interst I will report the findings back here. FWIW, the wound type filter is too restrictive to use unless the oil is pre-heated. My circulation pump puts out 60 psig and won't push cold oil through this filter.
PK

[bork]

Super ! keep us informed . those wound filters are offered in different ratings (micron)which micron rating don't know. GE is the manufacturer of these ,I beleive. I was at a seminar on water softners & GE put on the seminar. At time I didn't pay much attn but now I wish I had. I will look in the notebook provided for info & get back .