bypass pressure?
- Thread starter greystone
- Start date
- Status
the bypass press rating means the difference in pressure over the adbv, not total system pressure
Bypass pressure for the oil filter is a different pressure location than oil pressure.
The bypass in the oil filter is dealing with the pressure difference between 1 side of the filter media and the other side of the filter media.
As the media becomes more restrictive to the flow of oil due to dirt building up in the media or the oil being thicker due to being cold, the bypass in the oil filter will open when the pressure drop across the media becomes greater than the opening pressure of the bypass device, and oil will flow around the filter media, but the overall oil pressure to the rest of the motor, will STILL be maintained.
Think of it this way, the oil pump puts out oil at a pressure......say 20psi (just a round number for an example, the filter media causes a restriction of 5psi, leaving a oil pressure out of the filter of 15psi to flow to the places that the oil flows in the motor.
You have maintained enough oil pressure to maintain the proper oil flow to perform the lubrication requirements for the motor.
The bypass in the oil filter is dealing with the pressure difference between 1 side of the filter media and the other side of the filter media.
As the media becomes more restrictive to the flow of oil due to dirt building up in the media or the oil being thicker due to being cold, the bypass in the oil filter will open when the pressure drop across the media becomes greater than the opening pressure of the bypass device, and oil will flow around the filter media, but the overall oil pressure to the rest of the motor, will STILL be maintained.
Think of it this way, the oil pump puts out oil at a pressure......say 20psi (just a round number for an example, the filter media causes a restriction of 5psi, leaving a oil pressure out of the filter of 15psi to flow to the places that the oil flows in the motor.
You have maintained enough oil pressure to maintain the proper oil flow to perform the lubrication requirements for the motor.
Originally Posted By: Cause4Alarm
the bypass press rating means the difference in pressure over the adbv, not total system pressure
No it doesn't.
the bypass press rating means the difference in pressure over the adbv, not total system pressure
No it doesn't.
Quote:
say 20psi (just a round number for an example, the filter media causes a restriction of 5psi, leaving a oil pressure out of the filter of 15psi to flow
No it doesn't !
say 20psi (just a round number for an example, the filter media causes a restriction of 5psi, leaving a oil pressure out of the filter of 15psi to flow
No it doesn't !
Fluidics 101. Liquid can not be compressed. The system pressure is equal at all points.
The oil pump is a positive displacement pump. It's volume of flow is not going to be changed by a simple little filter.
The OIL FILTER has nothing to do with the SYSTEM PRESSURE. The system pressure is regulated by the oil pump relief valve. Most engines today that’s 60 to 80psi at operating speed.
When the FILTER MEIDA is restricting the flow through the FILTER at 10 to 15psi, the FILTER BYPASS opens to protect the filter media from being damaged.
The oil could be cold and thick, or the filter could be old an clogged.
I suggest that filter bypass is more common then we would like to believe.
The oil pump is a positive displacement pump. It's volume of flow is not going to be changed by a simple little filter.
The OIL FILTER has nothing to do with the SYSTEM PRESSURE. The system pressure is regulated by the oil pump relief valve. Most engines today that’s 60 to 80psi at operating speed.
When the FILTER MEIDA is restricting the flow through the FILTER at 10 to 15psi, the FILTER BYPASS opens to protect the filter media from being damaged.
The oil could be cold and thick, or the filter could be old an clogged.
I suggest that filter bypass is more common then we would like to believe.
Last edited:
If the filter media is clogged, then the pressure above the pressure relief valve theoretically could drop to zero and the positive displacement pump, which continues to pump oil at a pressure high enough to open the relief valve and flow continues. Is that not the condition that cause4alarm stated??
So basically, even if the oil flowing thru the filter is at 40 psi it does not mean there is 40psi on the bypass valve. Since there is equal 40psi on both sides of the valve. But, if the pressure on the input side of the valve is 15 to 20psi greater than the output side then it would open.
correct?
correct?
Last edited:
correct.....!
There are 2 pressures given.
1. Pressure at which the ADB membrane yields and lets oil into the filter.
2. Pressure at which the bypass valve opens, allowing oil to circumvent the filter media.
An important thing to consider is that the differential pressure that actually pushes against the bypass valve spring is really only the difference in pressure from one side of the filter media to the other.
It is NOT the oil pressure itself, which is likely significantly higher on either side of the filter media, but the fall in pressure over the restriction posed by the filter media that acts against the bypass valve spring.
So if oil pressure is 6 bar on one side of the filter media and 4.5 bar after it, the bypass will start to creep open.
And, if you think about it, even 1.5 bar is pretty high for what is basically paper.
1. Pressure at which the ADB membrane yields and lets oil into the filter.
2. Pressure at which the bypass valve opens, allowing oil to circumvent the filter media.
An important thing to consider is that the differential pressure that actually pushes against the bypass valve spring is really only the difference in pressure from one side of the filter media to the other.
It is NOT the oil pressure itself, which is likely significantly higher on either side of the filter media, but the fall in pressure over the restriction posed by the filter media that acts against the bypass valve spring.
So if oil pressure is 6 bar on one side of the filter media and 4.5 bar after it, the bypass will start to creep open.
And, if you think about it, even 1.5 bar is pretty high for what is basically paper.
Good explanation, but a personal observation of mine is that when an oil filter actually "clogs" and goes into full bypass, you will notice a dramatic drop in oil pressure; as much as 20 psi from normal. Installing a new filter will restore normal engine OP.
I've artificially induced a clogged filter condition when I experimented with an oil treatment many years ago called Restorer Engine Treatment (a compression restorer). The solid lead like material in the product inevitably clogs the oil filter.
I've artificially induced a clogged filter condition when I experimented with an oil treatment many years ago called Restorer Engine Treatment (a compression restorer). The solid lead like material in the product inevitably clogs the oil filter.
Pardon my ignorance, is the oil pressure sensor upstream of or after the oil filter?
If it's upstream, wouldn't that mean that oil flow to the bearings and everything else has improved in full bypass, actually?
If it's upstream, wouldn't that mean that oil flow to the bearings and everything else has improved in full bypass, actually?
Originally Posted By: maersk
Pardon my ignorance, is the oil pressure sensor upstream of or after the oil filter?
If it's upstream, wouldn't that mean that oil flow to the bearings and everything else has improved in full bypass, actually?
Of course, if the FF oil filter is clogged/reaches "by-pass me" pressure then the filter needs to bypass, you definitely NEED the oil to skip filtration and get to the vital engine parts.
When a FF oil filter is functioning properly and in non-bypass state, you are not only continuing to get oil to the areas in question, but it's being filtered on top of that.
Pardon my ignorance, is the oil pressure sensor upstream of or after the oil filter?
If it's upstream, wouldn't that mean that oil flow to the bearings and everything else has improved in full bypass, actually?
Of course, if the FF oil filter is clogged/reaches "by-pass me" pressure then the filter needs to bypass, you definitely NEED the oil to skip filtration and get to the vital engine parts.
When a FF oil filter is functioning properly and in non-bypass state, you are not only continuing to get oil to the areas in question, but it's being filtered on top of that.
- Joined
- Sep 28, 2002
- Messages
- 39,799
Most bypass events occur at cold start due to the engine oil pump going into pressure relief. Out of relief, the differential pressure across the filter is negligible..new or "seasoned". The engine, especially with thick oil cramming its way through it ..will be MEGA MORE restrictive than the filter. The filter is invisible in terms of pressure differential for most of you most of the time. When it's not, it is most likely during an oil pump relief event.
As a filter ages, it effectively simulates a smaller filter. So out of relief, at a given visc, at a given volume, you MAY create enough differential to have a bypass event. That would be rare.
As always, there are unicorns that popup from time to time ..and we are a nation of individuals that insist our situations are always unique.
As a filter ages, it effectively simulates a smaller filter. So out of relief, at a given visc, at a given volume, you MAY create enough differential to have a bypass event. That would be rare.
As always, there are unicorns that popup from time to time ..and we are a nation of individuals that insist our situations are always unique.
I pretty much agree with Gary Allan on this except (sort of) for the second part: On my truck, the differential pressure bumps up to the bypass setting of the stock size Wix filter I use at about 3K RPM (with hot oil). So whenever I punch the accelerator enough to cause a downshift at highway speed I am likely bypassing some of the oil around the element.
It will get filtered next time through, so no problem. Just an observation.
It will get filtered next time through, so no problem. Just an observation.
- Status