Wow, fantastic thread! I'd like to add some comments, if I may.
I don't think this test is valid in testing flow rates. I think the rate in which oil flows from outside to inside of the element has just as much to do with media porosity and osmosis, rather than flow created from a pressure differential between the outside and inside of the filter. At 6" of head, pressure at the bottom of the pan would only be 0.2 PSI.
I'd also like to say some things about efficiencies and beta ratios. As most of you have already commented, you have to take efficiency ratings with a grain of salt. Not only is it absolutely mandatory to communicate what particle size is being measured, beta ratio is a more important number than efficiency.
Any beta ratio over 10 looks like a fantastic number, because it would be 90% efficient (Eff=[beta-1]/beta). Even 97% or 99% looks like a great number. Still, a beta ratio of 100 (which is good in the automotive world) is [censored] in the fluid power industry.
A beta ratio is derived from counting the particles upstream of the filter, and dividing it by the particles counted downstream of the filter, normally in a multi-pass test. So if you had 10,000 particles upstream, and 1000 particles downstream, your beta ratio would be 10 (which is [censored]). If you had 10,000 particles upstream, and 10 particles downstream, your beta ratio is 1000, which is the common standard for high quality hydraulic filters (beta ratio 99.9%).
So big deal, 99.9% isn't that much better than 98%, right? Well 99.9% is a beta ratio of 1000, and 98% is a beta ratio of 50. That means that if you have 10,000 particles upstream, only 10 particles got through the beta 1000 filter. And if you have 10,000 particles upstream of the beta 50 filter, you have 200 particles downstream.
So that's 10 particles downstream compared to 200 particles downstream. The beta 1000 element is 20 times better at removing dirt than the beta 50 element.
Also important is the particle size that's listed with the beta ratio (a particle size must be listed, or it's a useless number). Any old filter can get 99% efficiency at 20 micron. Show me a automotive filter than can do 99% at 3 microns.
Hydac makes hydraulic filter elements that have a beta ratio of 1000 at 3 microns (99.9%), and you could even use them in your car.
river rat, I might be able to send you one of those elements for testing...
edit: wow, I can't believe c r a p gets censored!