I recently got interesting in oil filters. Ran across this thread while searching something else. I'll bet that happens a lot. A few random notes....
Micron ratings come in two flavors, absolute and nominal. Neither is useful for decision making without also stating the beta
value, effectively the percentage of a particular particle size captured by the filter.
I can claim my T-shirt will stop a 20 micron particle, and it probably will. However, the beta may be 2, i.e. 50% efficient, i.e. half the 20 micron particles pass through. Micron stated without a beta is just talk.
Most filter manufacturers test for a dual beta, i.e. beta at two particle sizes. If it's not published, ask. For example, the NAPA 1515 is a Wix 51515. The nominal micron rating is 21, but note the beta values, listed as 2/20=6/20. It means beta is "2" for a 6 micron particle and "20" for a 20 micron particle. A 2 beta means it is stopping 50% of the stated particle size, while a 20 beta is 95%.
Now look at the listing for bypass valve setting, 8 to 11 psi, about 25% lower than the bypass setting specified by Lycoming and Continental. It means dirty oil is bypassing the filter element more often than it does with a xx108 or xx109 internal bypass
Which raises another point. Screwing a NAPA 1515 onto a Lycoming adapter intended for use with a xx110 or xx111 filter effectively disables the adapter's 11-15 psi bypass. The 1515's bypass opens at a lower pressure.
A lower bypass opening pressure has nothing to do with burst pressure. The bypass relieves pressure across the filter element, but does not change can pressure.
Originally Posted by Northernliving
...I decided to cut some auto filters open after my last oil change for the purpose of looking at and measure some of the physical differences to the Tempest SpinEZ AA48110-2 filter I had been using.
These all seem to be good, well-constructed filters. The biggest difference that I noted was how the bi-pass filter was constructed. In the SpinEZ filter, it is internal to the filter spindle, the Wix had a spring at the filter end (bottom) and the entire media moved to open the bi-pass, and the K&N had a small simple spring bi-pass an the end (bottom).
Thank you Brian, but there are two misconceptions here. First, the AA48110-2 has no internal bypass, nor does the larger 48111. Same for the Champion versions. Pressure does not move the element. The bypass valve is in the engine's filter adapter. The leaf spring merely locates the element and holds it against the base plate. Same is true of the big coil spring found in the same locations in other filters.
The Wix bypass valve is the small top hat module sandwiched between the base plate and the filter element. It is self-contained; bypass flow is in through the holes you see around the perimeter, exiting into the center bore. Wix filters with no bypass substitute a module with the same external shape, but having no holes, internal diaphragm seal, or spring. It's just an inert filler.
The K&N pictured here does indeed have a poppet valve bypass, very similar to the bypass currently installed in the 108 and 109 aviation filters. I have not looked up its pressure rating.