That explaination is very good and makes sense.
But not what I was after. The Pressure differential across an element is a function of about 20 items. The only one we can find out about is the Relief valve pressure rating of about 10 to 15 pounds. You can find the spring that powers this function holding pressure against the bottom of the element pushing it up against the top of the can. You cannot find a relief valve however because there is none.
Should the element collect enough crap to meet the 10 pound limit, the excess inlet oil pressure just unseats the whole element from the top of the can, and oil flows directly from the little holes to the big hole.
This is the pressure on the inlet side of the element compared to the pressure on the outlet side of the element. It is called "Delta p" (Pressure differential). In normal situations of flow in the rated range of the element, at operating temperatures the actual "Delta P" may be only 2 pounds. No problems.
How much oil that an element can flow and not trip the bypass, all other features being equil, is a function of how much media area is flowing oil. So, if a Fram has 106 square inches of media, and a NAPA has 604 square inches of media (Actual measurements) the Fram will bypass oil early in the process rather than later. When the element is pushed down into the can, as part of the bypass function, all of the crap collected by the elemnt up to that point is available for flow out of the big hole. The NAPA (Wicks) will keep filtering and debris and will not be send it back to the dying bearing for a good long time without bypassing any oil.
The bypass value seems low, but in all but a major disaster the element will not bypass oil. However, In the cold weather, where oil may be like cement, and that imbecile across the street revs up the engine to warm the oil quickly, he has the element in bypass, and the engine is doomed.
In real aircraft filters, there is a colored plunger that pops out of the filter head, to warn you that the filter (Delta-P) has approached its bypass value, and service is required. Pretty cool stuff. If you are sure the cooler is sterile, the filter can be in front of it. If not, the filter should be behind it. Warm the oil before full throttle operation.
Lynn E. Hanover
In a message dated 4/7/2008 7:29:42 AM Pacific Daylight Time, keltro@att.net writes:
Ed, Lynn and All,
The way I understood Lynn's reply was as follows........The oil
cooler has more flow capacity than the oil filter (at least a single
filter that most of us use).........The restriction caused by putting
the filter before the cooler has the potential of allowing the bypass
of the filter to open (pressure differential due to the lower flow
capacity of the filter) thereby allowing trash captured by the filter
to flow through the cooler and on to the engine........By locating
the filter after the cooler the chance of this occurring is much less
because of lower flow demands of the engine bearing system.......
Hope this makes sense.........Is that anywhere near to what you
were talking about Lynn ??
--
Kelly Troyer