Only time an extension of time to build oil pressure due to an oil filter (not including an initial start-up after an filter change) would be if the filter ADBV is allowing oil to drain down from the engine galleries and filter, or if the filter is super restrictive and caused the oil pump to hit well into pressure relief and thereby cut way back on oil flow volume to the oiling system.
Not necessarily. I’ve tested this actually in a professional setting.
More volume in the system lowers the bulk modulus. This makes the system less “hydraulically stiff”.
The measured rate of pressure rise vs flowed volume is less than calculated. This is because calculations assume equal stiffness which real parts don’t have.
For example, you can replace a run of -12 hose in a hydraulic system with an equal length of -16 hose, and you will measure lower restriction but find that it takes longer to build pressure. Restriction is better but pressure delay is worse, even with no air present.
It’s simply a function of the total volume that must be pressurized and how “stiff” it is hydraulically. Larger volumes lose modulus.
Incidentally, this is primarily how air in the filters cause oil pressure delay. Air is a fluid and will transmit pressure just like oil will. It’s just that air is so much more compressible that it takes more oil displacement to build pressure against it. Hence the delay.
The underlying physics are the same whether the bulk modulus decrease happens because of the fluid being more compressible (air), or because the fluid container increases in volume.
So, if all else is equal, even with zero air present, a larger filter can takes longer to build pressure. At the scale of PCMO filters, it’s in the order of milliseconds and not significant, imo. But it is nonetheless a very real and measurable phenomenon.
At the scale of the engines I do for work, where filters hold 3 or 4 gallons of fluid, it’s a quite significant thing that I have to design and engineer around.
