"assuming the relief is closed" is being used as a qualifier to the statement that a PD pump will give the same flow regardless of viscosity oil but in the real world the relief will not be closed. We have a chart showing the relief opening at 2000 rpm and I'm assuming that is with the oil up to temperature. I have an engine where I know the relief is designed to open at or before.2000 rpm even with hot oil. When the oil is cold I believe the relief will be open from idle onwards. So particularly for cold oil it seem clear to me that while a PD pump can deliver the same flow rates at it's output irrespective of viscosity, some of that flow is being lost to the relief valve such that the flow rate to the engine galleries is not the the same with practical consequences for example time to deliver oil to the top end at start up.
When the pump starts going into pressure relief depends on a lot of things ... one of them being the design of the oiling system and pump itself including the pressure relief valve, and of course the oil viscosity at any given moment. Most normal vehicles on the road even at high RPM can't achieve max oil pressure with hot oil to trigger pump pressure relief - maybe if the oil filter is clogged is one case where pump pressure relief could happen with hot oil."assuming the relief is closed" is being used as a qualifier to the statement that a PD pump will give the same flow regardless of viscosity oil but in the real world the relief will not be closed. We have a chart showing the relief opening at 2000 rpm and I'm assuming that is with the oil up to temperature. I have an engine where I know the relief is designed to open at or before.2000 rpm even with hot oil. When the oil is cold I believe the relief will be open from idle onwards. So particularly for cold oil it seem clear to me that while a PD pump can deliver the same flow rates at it's output irrespective of viscosity, some of that flow is being lost to the relief valve such that the flow rate to the engine galleries is not the the same with practical consequences for example time to deliver oil to the top end at start up.
Sounds like a little back peddling...When the pump starts going into pressure relief depends on a lot of things ... one of them being the design of the oiling system and pump itself including the pressure relief valve, and of course the oil viscosity at any given moment. Most normal vehicles on the road even at high RPM can't achieve max oil pressure with hot oil to trigger pump pressure relief - maybe if the oil filter is clogged is one case where pump pressure relief could happen with hot oil.
And as mentioned, even though a PD is in pressure relief, there is still going to be increased oil flow as the RPM increases like the chart shows. No mechanical spring loaded relief valve is going to regulate a perfect rock steady maximum oil pressure after it starts opening as RPM keeps increasing, and how well it regulates the max pump output pressure and flow also depends on the flow performance/size of the relieve valve.
WRT to your last sentence, it all depends on the temperature and viscosity of the oil. If it's super cold and thick, and barely pumpable then the pump might have a hard time getting oil to its inlet and pumpability will suffer. If the oil is pumpable, then the relief valve could/might open momentarily depending on many factors, but most engines don't rev much above 1500 RPM on cold starts, so keeping the RPM down until the oil warms up some helps mitigate pump relief. Bottom line is PD pumps are used for a reason, and that is to ensure adequate oil lubrication to the engine over a very broad range of use conditions.
Like what?Sounds like a little back peddling...
‘A useless point to debate in reality.... but....
Interesting that the 167 page governing document:
Engine Oil Licensing and Certification System
API 1509
EIGHTEENTH EDITION, JUNE 2019
never once mentions the word “Winter.”
I spoke to an SAE engineer some years ago (when I was a member) and asked what the W stood for. He said no word in particular, that it could have been any other letter.
Same PDP, same RPM...
Thicker, higher viscosity oil (more resistant to flow) may flow the same volume at the same RPM but it will make the pump work harder to do so (hence resistance). The phrase "more resistant to flow" is in relation to an ICE and the level of resistance each viscosity demonstrates while in use.
Yes, and also why oil pressure goes down at the same RPM with the same oil as the oil warms up and becomes less viscous. When the pump not in relief of course.Same PDP, same RPM...
Thicker, higher viscosity oil (more resistant to flow) may flow the same volume at the same RPM but it will make the pump work harder to do so (hence resistance).
A journal bearing doesn't act as a fixed orifice as speed varies.... If the system is limited to say 80 PSI then no amount of pump output will increase the flow unless the pressure is allowed to also increase. If there is no increase in the pressure then no increase in flow is possible. ...
I disagree that after hitting the pressure relief point the engine oil flow can still increase with increasing RPM. A fluid can only move if there is a difference in pressure. If the system is limited to say 80 PSI then no amount of pump output will increase the flow unless the pressure is allowed to also increase. If there is no increase in the pressure then no increase in flow is possible. In all my vehicles the pressure hits the relief point and increases no further, regardless of the RPM. Therefore flow cannot increase further. Oil flow is limited to that amount when the maximum pressure is encountered, sometimes at just a few thousand RPM. Again, later chapters will make this clear.
As I mentioned, the roll-off of flow throughout the RPM range is dependent on many things: 1) Pump slip/efficiency, 2) oil viscosity, 3) Design and size of the pressure relief valve. Look at the graph, and you can see even as more and more flow is being shunted and not flowing into the engine, there is still increasing flow going through the engine. It's not as much increase as if the pump wasn't in relief, but flow is still increasing with RPM. As far as your Ferrari, who know for sure. Are you revving the engine to near redline with relatively cold oil when you're looking at how the pressure increases with RPM? If not, then it's an incomplete test. And what oil viscosity are you using while doing that experiment?I disagree that after hitting the pressure relief point the engine oil flow can still increase with increasing RPM. A fluid can only move if there is a difference in pressure. If the system is limited to say 80 PSI then no amount of pump output will increase the flow unless the pressure is allowed to also increase. If there is no increase in the pressure then no increase in flow is possible. In all my vehicles the pressure hits the relief point and increases no further, regardless of the RPM. Therefore flow cannot increase further.
You might want to do some more studies on PD pumps used in an ICE, and how the pressure relief valve come into play and operates.Oil flow is limited to that amount when the maximum pressure is encountered, sometimes at just a few thousand RPM. Again, later chapters will make this clear.
So part of what you're saying is people don't get that spring loaded relief valves don't just necessarily open wide up and stay open, they constantly modulate open and shut as the valve will begining springing open when the inlet and outlet pressures are at a certain delta, but by opening the relief valve that delta decreases and the valve starts shutting but as the restriction grows stronger it starts opening back up more and more or less the valve constantly modulates while in relief, which on a similar note is why in Fram marketing materials they make such a big deal out of their oil filter bypass valves surviving millions of cycles.I imagine if someone designed a computer controlled pressure relief valve based on a sensitive pressure gauge, then the pressure could be controlled dead nuts. Oil pump pressure relief valves are just a spring loaded device, with a linear force spring.
Look at the video OVERKILL posted in post #23. He says the pressure relief valve is set to 65 PSI, yet as he keeps revving the engine when the oil pressure hits 65 PSI, the oil pressure keeps increasing some because the pressure relief is unable to max the pressure at 65 PSI. This is a typical control characteristic of a spring loaded relief valve that isn't super sized to bypass the shunted oil around the pump without some flow loss.
Sure … for example cars today will have 8 speed to 10 speed transmissions - so the oil pump and PRV must repeat this pattern several times during spirited acceleration …So part of what you're saying is people don't get that spring loaded relief valves don't just necessarily open wide up and stay open, they constantly modulate open and shut as the valve will begining springing open when the inlet and outlet pressures are at a certain delta, but by opening the relief valve that delta decreases and the valve starts shutting but as the restriction grows stronger it starts opening back up more and more or less the valve constantly modulates while in relief, which on a similar note is why in Fram marketing materials they make such a big deal out of their oil filter bypass valves surviving millions of cycles.
That graph and its title are not clear whether it's about actual flow to each component, or optimum flow.... Look at the graph, and you can see even as more and more flow is being shunted and not flowing into the engine, there is still increasing flow going through the engine. It's not as much increase as if the pump wasn't in relief, but flow is still increasing with RPM. ...
I imagine if someone designed a computer controlled pressure relief valve based on a sensitive pressure gauge, then the pressure could be controlled dead nuts. Oil pump pressure relief valves are just a spring loaded device, with a linear force spring.
Indeed … it’s a hydraulic system these days … VVT … AFM … piston jets … variable output oil pumps … ECM controls/sensors …That graph and its title are not clear whether it's about actual flow to each component, or optimum flow.
Inability of a typical relief valve to maintain its exact nominal setting isn't the only reason flow rate varies with speed.
Correct, a spring loaded valve (like a PD pump pressure relief valve, or a filter bypass valve) just doesn't open all the way when they start to crack open. They gradually open, and require more and more force (delta PSI across the spring loaded valve) to open farther in order to flow more volume. It's not a "step function", and therefore you will see something similar to the graph in post #16. In order to have a step function pressure relief valve, it would have to actuated (computer controlled) to open the correct amount based on the delta PSI across it to keep the pump outlet pressure dead nuts constant.So part of what you're saying is people don't get that spring loaded relief valves don't just necessarily open wide up and stay open, they constantly modulate open and shut as the valve will begining springing open when the inlet and outlet pressures are at a certain delta, but by opening the relief valve that delta decreases and the valve starts shutting but as the restriction grows stronger it starts opening back up more and more or less the valve constantly modulates while in relief, which on a similar note is why in Fram marketing materials they make such a big deal out of their oil filter bypass valves surviving millions of cycles.