A filter bypass question to educate me

[rav]

Can anyone explain to this old jarhead how the oil filter bypass valve functions? I know that most spin on filters have a 20 to 25 psi bypass specs but i my 2017 Silverado with the 5.3l engine has a 40 PSI gauge reading, hat keeps the RV from opening? Is it a pressure deferential? is it that 40psi oil is on both sides of the filtration media, (no PSI difference between them) so it stays closed?

I also noticed that when my trucks "downhill braking" kicks in & the RPMs go over 3500, the oil pressure jumps to 60 PSI, will the RV still stay closed?

Please help this 76-year-old jarhead to understand.

 

[fantastic]

40 PSI Guage reading? Are you referring to the oil pressure gauge on the dash? Regardless the pressure inside the can can be different (lower). The media acts as "Resistance" to flow when it's loaded or has cold (thick) oil that prevents flowing through the media. If the media is restrictive over 25 psi then it will open bypass. There seems to be a range of bypass though rather than a light switch like bypass event. Bypass might open slightly but still allow some oil to flow through the media. But I think you understand it correctly.

 

[bullwinkle]

The bypass is delta-P, differential between the outside of the filter media & the inside that's connected to the oil system in the engine. If you have really thick, cold oil & it can't get through the media, the bypass could open a little to allow the inside & outside to remain in range, depending on what the filter bypass setting is. As the oil gets hotter & thinner, it can get through the media more easily, and WOT redline events might not even be enough to open it.

 

[oil pan 4]

As the oil flows it loses pressure, one of the biggest restrictions in the engine can be the oil filter. Even a new clean filter can drop 1 or 2 psi as the oil flows across it.
Most oil filters by pass some where between 7 to 12psi of pressure drop. A new clean filter probably doesn't bypass any oil.
Cold starts and well used oil filter probably bypass some.

 

[ZeeOSix]

As the oil flows it loses pressure, one of the biggest restrictions in the engine can be the oil filter.

The journal bearings are actually the biggest flow restrictions in an engine. A typical oil filter is only around 1/15th of the total restriction of the oiling system.

 

[ZeeOSix]

Can anyone explain to this old jarhead how the oil filter bypass valve functions? I know that most spin on filters have a 20 to 25 psi bypass specs but i my 2017 Silverado with the 5.3l engine has a 40 PSI gauge reading, hat keeps the RV from opening? Is it a pressure deferential? is it that 40psi oil is on both sides of the filtration media, (no PSI difference between them) so it stays closed?

Yes, the bypass valve inside the oil filter only operates on the pressure differential across the oil filter, as already mentioned. The oil pressure on your dash is the oil pressure measured at the oil pressure sensor location, and is an indication of the total oil pressure being supplied to the engine. The filter bypass valve is basically a spring loaded check valve. It only lets oil flow from the high pressure side (the dirty side) of the filter to the low pressure side (the clean side of the filter). The spring is matched to the size of the bypass valve in order to start cracking open at the desired PSI acting on it.

The dP across the oil filter is a function of: 1) The flow resistance of the filter itself, 2) The flow rate of the oil going through it, and 3) The viscosity of the oil. If you were to fire up a cold engine and rev it to 5000 RPM, then that cold thick oil at a high flow rate would cause enough dP across the filter to open its bypass valve.

Another example is that you could have 80 PSI of oil pressure, but the flow and viscosity of the oil going through the filter might only produce 5 PSI of dP across the filter, and that would not open the bypass valve.

 

[BrainThicknessVariation]

Flow is caused by a pressure difference. If the pressure difference between the inlet and outlet is greater than the rating of the oil filter, the valve opens. This ensures your engine is not starved of oil by guaranteeing a minimum "flow rate". This PSI rating varies between brands due to differences in filter media, and radius of the oil filter's inlet and outlet holes.

Here's a good explanation.

And here.

And a cool animation

 

[ZeeOSix]

Flow is caused by a pressure difference.

To add ... another thing to realize with flow is that resistance causes a pressure drop. A good example of that would be if the pressure at the inlet of a garden hose is 60 PSI, and it's 0 PSI at the end of the hose (Atm pressure = 0 gauge pressure), then the constant flow of water through the hose caused a 60 PSI drop from the inlet to outlet due to the friction between the water and hose. You can have pressure without flow, but you can't have flow without pressure.

If the pressure difference between the inlet and outlet is greater than the rating of the oil filter, the valve opens. This ensures your engine is not starved of oil by guaranteeing a minimum "flow rate". This PSI rating varies between brands due to differences in filter media, and radius of the oil filter's inlet and outlet holes.

The filter's bypass valve only operates on the dP across the valve itself, so that means from the dP across the media and the center tube only. The filter's inlet and outlet holes are not part of the dP directly across the bypass valve.

The bypass valve's function and purpose is also to help protect the filter from damage due to the dP across the media and center tube. Filters with pretty high bypass valve settings (ie, over 20 PSI) need to be built well to withstand that level of pressure across the media/center tube.

 

[ZeeOSix]

And a cool animation

What's wrong with that animation is when the bypass valve opens, only a small portion of the flow goes through it, not all of the flow like shown in the animation. There would still be the majority of oil going through the media to be filtered. It would only work as shown if the media was 100% clogged, but filters normally don't get clogged 100% so all the oil goes through the bypass valve. The media would probably fail/tear too if it was 100% clogged. A brand new oil filter can go into bypass under the right operating conditions (ie, thick oil with high RPM).

 

[BrainThicknessVariation]

To add ... another thing to realize with flow is that resistance causes a pressure drop. A good example of that would be if the pressure at the inlet of a garden hose is 60 PSI, and it's 0 PSI at the end of the hose (Atm pressure = 0 gauge pressure), then the constant flow of water through the hose caused a 60 PSI drop from the inlet to outlet due to the friction between the water and hose. You can have pressure without flow, but you can't have flow without pressure.


The filter's bypass valve only operates on the dP across the valve itself, so that means from the dP across the media and the center tube only. The filter's inlet and outlet holes are not part of the dP directly across the bypass valve.

The bypass valve's function and purpose is also to help protect the filter from damage due to the dP across the media and center tube. Filters with pretty high bypass valve settings (ie, over 20 PSI) need to be built well to withstand that level of pressure across the media/center tube.

I was trying to simplify it

 

[ZeeOSix]

I was trying to simplify it

So was I with some added information.