TallPaul,
Yes, filter company give multiple testing spec's.
On my beat up Greshen
TWA Beta 10=2
TWA Btea 20=20
TWA Beta 22=75
Capacity 8 gms Typical
Delta P @ 10gpm (with) 150 SSU= 4 PSID
Suppose it said 10 PSID? Does that mean in all instances that there will be 10 PSID using a 150 SSU fluid flowing @ 10gpm? Suppose it's running through a ZERO pressure return line? There it works. Suppose it's pumping through a .0135 orifice? Suppose it's a tight engine with a low volume oil pump ..or a loose one with a low volume oil pump
Those things will not alter the flow ..but they will alter how much back pressure is seen by the filter, altering it's "proportion" of total pressure drop in a fluid circuit.
These are static spec's that can't be taken out of context and templated upon how they will appear "in line".
They work for
comparison purposes only.
In the aforementioned Greshen, Suppose I put it under its max recommended operating pressure, and put a choke on the outlet that reduces the flow to 10gpm with a 150 SSU fluid? Do you think that you would still see 4 PSID??
These are not easy things to envision.
Take your old DC electricity test from 4th grade. You apply your 3V dry cell and find that the bulb drops 3v. Now evolve that to putting two bulbs in series ..just like they did in the class room and they show us that they both drop 1.5V ..and add up to the 3V supply.
Now let's alter the test. Make the second bulb 10X the resistance of the original bulb. NOW you see that our original bulb drops 1/10th the original (original reading with 3V applied) voltage ..and the other bulb drops 10X what the lower resistance bulb.
How can this be? The first bulb dropped 3V in the first test??
So, let's say that we had an ammeter installed in line. When we did our single bulb test, we found that THIS bulb had 1 amp at 3V applied pressure. Now we take our 10X bulb and CRANK UP the voltage until we, once again ..get our 1 amp of flow. LOOK!! LOOK! the bulb still drops the same 3volts. I guess I was wrong ...but now our applied voltage is 33VDC ...so I guess I was right. If we applied 33VDC to the original bulb by itself ..we'd no have 11 amps ..not the original 1 amp that (would give us if viewed from current applied/consumed) produced 3VDC.
This is ESSENTIALLY what occurs. There are minor drifts off of that basic rule (inherent pump losses, viscosity to a very limited degree) etc.)..but that's essentially it in a nutshell WHENEVER the flow is at unity with what the pump is producing in current and what the engine is receiving in current. That is, a series circuit (from the above and below media/filter view). Now when the relief circuit of the oil pump is open that is no longer the case. You DON'T have continuity in your flow ..some of it can go somewhere else.