Originally Posted By: Trvlr500
I have a question maybe someone can answer. I read in a couple earlier posts that the relief valve on a couple of different filters is set at 16psi or 12psi for the Ultra. How does a filter like that work when the oil pressure runs at a constant 30-40 psi hot or cold? Or are the various filters designed with different pressures for by-pass depending on the engine?
You're confusing oil pressure and bypass pressure (differential pressure). With a clean filter at a given flow rate and oil temp/viscosity, there is only a few PSI difference in the oil pressure before the filter and after the filter. That's differential pressure (aka DP or Delta-P). As the filter loads up, that DP increases. When it reaches the preset DP bypass valve setting, the valve bypasses some or all of the oil to make sure the engine has enough oil flow.
When the oil is cold and thick it's harder for it to push thru the filter, so the DP is higher and the bypass may open. Whether or not (or how often) that happens is dependent upon the restriction downstream of the filter. Once the system is fully pressurized, the oil galleries are far more restrictive than the filter.
The engine manufacturer sets the bypass opening spec according to the OE baseline filter efficiency and flow specs it was designed forbut in reality, the engine doesn't care all that much as long as it has sufficient oil flow at and below max DP.
I have a question maybe someone can answer. I read in a couple earlier posts that the relief valve on a couple of different filters is set at 16psi or 12psi for the Ultra. How does a filter like that work when the oil pressure runs at a constant 30-40 psi hot or cold? Or are the various filters designed with different pressures for by-pass depending on the engine?
You're confusing oil pressure and bypass pressure (differential pressure). With a clean filter at a given flow rate and oil temp/viscosity, there is only a few PSI difference in the oil pressure before the filter and after the filter. That's differential pressure (aka DP or Delta-P). As the filter loads up, that DP increases. When it reaches the preset DP bypass valve setting, the valve bypasses some or all of the oil to make sure the engine has enough oil flow.
When the oil is cold and thick it's harder for it to push thru the filter, so the DP is higher and the bypass may open. Whether or not (or how often) that happens is dependent upon the restriction downstream of the filter. Once the system is fully pressurized, the oil galleries are far more restrictive than the filter.
The engine manufacturer sets the bypass opening spec according to the OE baseline filter efficiency and flow specs it was designed forbut in reality, the engine doesn't care all that much as long as it has sufficient oil flow at and below max DP.
