Filtration vs Flow vs Pressure Relief

[Bristol603]

I have been reading this board for a while trying to educate myself. With oil filters there seems to be a trade off between flow rate and minimum particle filtration size. In one camp there might be a K&N filter with good flow and in the other an Mobil 1 filter which works down to a low particle size.

My question concerns which of these design choices is likely to be most benefical for good condition, mixed use engine. My car has a 5.9l Mopar V8 300hp crate engine. This now has about 20000m on it and runs well on a diet of Delvac 1. The oil pressure at anything over 1500rpm, even when fully hot, hits the peg at 80psi. At a 700rpm idle its about 40psi when hot.

At 80psi I am assuming that the oil pressure relief system is working and so the flow has reached a maximum level which is not being limited by the oil filter, but is being limited by not wanting to subject the engine to excessive oil pressure. If this is correct, then a high flow K&N type filter doesn't gain me much and a small particle filtration Mobil 1 type filter might be better since its advantage isn't altered by such behaviour.

I know you gentlemen know more than I'll ever know about this, and so I would be grateful if you could correct or confim this line of reasoning.

Thank you.

 

[T-Keith]

I think until we get a comparable test(ie Grease's) we won't know where the Mobil 1 filter stands. If you want maximum filtration I think that the Purolator Pure One, would be on top. If you think your getting enough flow with the Purolator, then go with that one.

I think with that much flow and that thick of oil, I would go with the K&N.

-T

 

[Bristol603]

Thanks for the reply.

I have run it with an Mobil 1 filter and it currently has a K&N on it. With both, the oil pressure hits the maximum as soon as you start moving. If I am running with the oil pressure relief system limiting the pressure (and therefore flow), then would the Mobil 1 and K&N be flowing essentially the same (so I might as well go for the Mobil 1)? I have a nasty feeling this may be a dumb question!

PS - The Mopar instructions for the engine spec a 10W30 or 20W50(!). Synthetic 10W30 is hard to find in the UK (Mobil don't sell their 10W30 here) so I settled on Delvac 1 5W40 having read of it here. The engine does have high volume oil pump as standard.

 

[T-Keith]

Wow, it sounds like you have a lot of flow. Perhaps any filter will be in bypass most of the time. Then I'd lean toward a good bypass(like motorcraft), or a high flow filter(like the K&N) to reduce time in bypass(if possible).

-T

 

[dickwells]

We have to keep in mind, as always, that the pressure within the oil system has no effect on the bypass valve. The bypass valve only acts on pressure differences within the system, and we have no gauge to let us know what they may be. We would need a gauge reading before the filter and another after the filter. When the difference between the two readings was 18psi or whatever, we could assume the valve is open. The only time the valve is usually open is probably on startup, and particularly with bad backflow preventers which allow the galleries to empty between starts, so they must be refilled each time the engine starts.

 

[needtoknow]

Because the oil system is not dead heading (zero flow) then you don't know if the oil pressure relief valve is opening at 80psi or not. You need to know the relief valve setting. I doubt the relief valve is controlling the system oil pressure as this would create extra heat as the oil flows across the relief valve. These relief valves are only fail safe valves not meant for pressure control. I would imagine the engineers designed the flow rate of the pump verses the leakage through the bearing surfaces to reach the operating pressure of the engine they wanted.
That's why on older engines with worn bearings the oil pressure can be less because there is less restriction to flow. You would also need to know the relief valve setting of the oil filter to understand when it will by-pass. Without a pressure verse flow diagram the only way to know this is a flow test. I'm no expert on proper oil pressure in engines but yours sounds quite high for what I'm used to seeing. What does your owners manual say? You could go with a larger filter with higher filtration which would offset the supposed higher restriction but you may need to go with a remote mount oil filter to achieve this. I have tried to get flow specifications from Melnor Pumps but have not had much luck. They engineer their pumps by buying an OEM and tearing it apart to take measurments.

 

[Michael SR]

quote:

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Originally posted by needtoknow:
Because the oil system is not dead heading (zero flow) then you don't know if the oil pressure relief valve is opening at 80psi or not. You need to know the relief valve setting. I doubt the relief valve is controlling the system oil pressure as this would create extra heat as the oil flows across the relief valve.

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if you're talking about the "relief valve" in the oil pump, it is indeed bypassing on just about every engine past a certain rpm. and yes, this does heat the oil because most pumps bypass internally, so some measure of the oil keeps getting compressed over and over.

i've seen a few cases where the bypass valve in the pump stuck open, and some where they stuck closed. in the stuck closed scenario the oil filter would instantly pop if it were a regular one, and deform until it leaked if a heavy-duty race one. stuck open you'd be hard pressed to reach 30psi in a hot engine.

as far as the original question, i'm not so certain the filter is in bypass as much as you think. i've run both a PF1218 and a K&N3002 on my car, with the filter bypass in the block disabled, and saw only about a 5psi drop as compared to running a filter bypass. (this is fully warmed up.) a 5psi pressure differential is below most filter's bypass valve setting, correct?

-michael

 

[Gary Allan]

The function of the bypass, as others have mentioned, is realized when the filter "sees" this differential.

It is also typically assumed that it is in use when the filter blocks. IMHO even if the bypass is open on a clean filter ...it's still filtering. I run a Amsoil bypass next to a full flow...comparatively the ff is an open pipe compared to the bypass ..yet the bypass sees flow after warm up (for the conceptionally challenged the parallel is that the full flow in this case is the "bypass valve" in a single ff setup and the bypass filter represents the filter media). In a HV situation ..the particle count would probably be no different since all the oil (sooner or later) will see the element.

 

[T-Keith]

quote:

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Originally posted by dickwells:
We have to keep in mind, as always, that the pressure within the oil system has no effect on the bypass valve. The bypass valve only acts on pressure differences within the system, and we have no gauge to let us know what they may be. We would need a gauge reading before the filter and another after the filter. When the difference between the two readings was 18psi or whatever, we could assume the valve is open. The only time the valve is usually open is probably on startup, and particularly with bad backflow preventers which allow the galleries to empty between starts, so they must be refilled each time the engine starts.

---

Your right oil pressure has no direct influence on bypass operation. However high flow would logically lead to more filter pressure difference, as would a restrictive filter. Since he's experiencing 80 psi at idle, I would say that he has very high flow, therefor leading to more bypass operation.

needtoknow brings up a good point too, are we sure the pressure relief valve is operating?

-T

 

[Schultz]

If you guys are really interested in seeing when your engine is in bypass and you have a remote filter then all you need to do is install a hydraulic bypass switch on the remote filter head. They are pre set to close a switch contact at a differential pressure of 15 & 25 psi. This contact can be connected to power and a light to show you your filter is in bypass mode. But your filters bypass would have to correspond to the switches pressure setting.
These can be gotten from Parker, Pall, and others for around $70.

 

[Bristol603]

I was imagining it was the pressure relief valve on the oil pump which was opening and limiting the oil pressure to 80psi. The spec for the production engine (doesn't have high volume oil pump) is oil pressure 30-80psi@3000. The same book also list "Oil Pressure Bypass Valve Setting" as 9-15psi.

I am now getting confused. I thought the bypass on the pump was to stop the absolute pressure going too high and was typically about 80psi. The bypass on the filter was to stop the differential pressure on the filter getting too high (say the 9-15psi). Am I getting this all wrong?

Thanks.

 

[Michael SR]

quote:

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Originally posted by Bristol603:
I am now getting confused. I thought the bypass on the pump was to stop the absolute pressure going too high and was typically about 80psi. The bypass on the filter was to stop the differential pressure on the filter getting too high (say the 9-15psi). Am I getting this all wrong?

---

no, you're spot on.

-michael

 

[T-Keith]

Your right, I'm not sure why you would be thinking otherwise.

-T

 

[Bill Kapaun]

Bristol-
Do you have room for a longer filter such as the Motor Craft Fl-1A or even the FL-299 equivalents.
The greater area of the media should reduce pressure differential etc.

 

[TC]

Bristol: Some firms, such as Wix and Baldwin, will tell you a filter's total area (such as "200 square inches") if you e-mail them. Other media areas have been determined by studies on this board and elsewhere. If you simply obtain a large-area "oversize" filter with a fine-filtering media (such as PureOne, Mobil 1, Baldwin, etc.), you should be getting the best of both worlds, relatively high flow (due to a large cartridge) and high filtration. But keep in mind that some large cans actually contain small cartridges, and some small cans (such as Subarus) actually pack a large amount of media inside -- looks alone can be deceiving.

 

[needtoknow]

Originally posted by Michael SR:
if you're talking about the "relief valve" in the oil pump, it is indeed bypassing on just about every engine past a certain rpm. and yes, this does heat the oil because most pumps bypass internally, so some measure of the oil keeps getting compressed over and over.
end quote

It would be good to know what type of relief valve is most often used. I would assume the pumps are gear pumps but maybe vane. If they are direct operated relief these typically, from my industrial hydraulics background, are not metering valves. There is some metering at the cracking pressure of the spring but at a certain pressure they are full flow valves. I would not think that dumping the entire flow back to the pan would be a good thing in any circumstance. The internal leakage is a characteristic of pump construction and would also be figured into the equation but I suspect it is a small amount, at least on a new pump. When the engine is cold and pressure is 60psi is the relef valve dumping, when the engine is hot and pressure is 30psi is the relief valve dumping? I doubt it. Maybe a pressure compensated flow control is used to regulate pressure?? Pump pumps max 15gpm, constant flow over the PCFC 3gpm at higher pressures the valve adjusts to still flow 3gpm leaving the remainder to flow to the engine. There will never be no flow to the engine. Just thinking without being the auto engineer. It's hard to engineer a direct acting relief valve spring for all conditions and flow but I'm used to 60gpm and 2500psi, maybe 5gpm and 60psi makes it easier.

[ May 20, 2004, 04:00 PM: Message edited by: needtoknow ]

 

[Michael SR]

quote:

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Originally posted by needtoknow:
It would be good to know what type of relief valve is most often used. I would assume the pumps are gear pumps but maybe vane.

---

i'm afraid i wasn't quite sure what you were trying to say overall, but let me try and address each thing individually.

oil pumps are mostly gerotor pumps, i've never seen a vane pump as an oil pump on a production engine. (but there might be some!)

quote:

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if they are direct operated relief these typically, from my industrial hydraulics background, are not metering valves. There is some metering at the cracking pressure of the spring but at a certain pressure they are full flow valves.

---

i'm not sure what the term "direct operated relief" means, can you clarify?

the bypass valves are usually a spring-loaded piston. if the piston moves in against the spring far enough, it will progressivly open an orifice that connects the pressure side and suction side of the gears.

in any case, the pumps i've seen do not have a bypass passage large enough to match the pump's flow rate. even stuck wide open there's still pressure seen at the engine. (it's pretty obvious from eyeballing the bypass system that it can't flow enough.)

when the oil is cold and the engine a fair amount above idle, the valve is as open as it can go, yet oil pressure is usually still at or past the bypass pressure. on a typical american V8, a stuck fully open bypass valve means the oil pressure is ~5psi or less at idle (hot), and maybe 20-30psi at cruising speed. (this is referenced to an engine that will hot idle at 35-40psi, and 60psi at 2.5k rpm.)

quote:

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I would not think that dumping the entire flow back to the pan would be a good thing in any circumstance.

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speaking of bypassing to the pan, i know some racers modify their oiling systems so that the pump is full flow only. then, on the opposite end of the oiling system (usually at one of the galley plugs), they have a stand-alone relief valve which bypasses excess pressure/oil directly back to the pan, rather than have it ceaselessly circulate within a pump with a bypass.

i'm not sure that buys them much, but i don't really know. i'm not very knowledgable about race dry sump oiling systems, but i suspect the bypass design i just described originated with dry sump systems.

quote:

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The internal leakage is a characteristic of pump construction and would also be figured into the equation but I suspect it is a small amount, at least on a new pump.

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agreed, we're definitely talking about a separate valve and not just internal leakage.

quote:

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When the engine is cold and pressure is 60psi is the relef valve dumping, when the engine is hot and pressure is 30psi is the relief valve dumping? I doubt it.

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right. i'd like to know for sure, but i don't think the valve is bypassing anything in your second scenario. however, even with hot oil, it doesn't take much rpm to hit open the bypass valve. the engine in my vette pegs its oil pressure hot by 2500rpm, albeit with a high volume pump. but even stock it still pegged at the bypass pressure by 3500rpm.

quote:

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a pressure compensated flow control is used to regulate pressure?? Pump pumps max 15gpm, constant flow over the PCFC 3gpm at higher pressures the valve adjusts to still flow 3gpm leaving the remainder to flow to the engine.

---

ah, ok, i finally understood that. no, i don't think it works like that. i think it just reacts by bleeding off flow once the pressure reaches a certain amount.

on some pumps the spring is even user serviceable, btw.

quote:

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It's hard to engineer a direct acting relief valve spring for all conditions and flow

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definitely, that's why oil pressure doesn't follow the identical signature in all circumstances. but, i am surprised at how well it does seem to work. the size of the bypass has to be engineered to match the viscosity, flow rate, and engine demand, yet somehow stock pumps work with a huge range of engine mods, different oils, etc.

-michael

 

[needtoknow]

Michael, I'm getting a better picture of the pump design, since I've never seen one. Direct acting just means that pressure acts directly on the spring not through a separate pilot operated setup. From your description what you call a relief valve, I may call a pressure compensated flow control. If the size of the unloading orifice is adjusted to pressure then I would consider that a pressure comp. flow control. Either way pressure is being controlled by controlling flow. The size if the fixed orifice that returns dumped oil back to inlet being a final failsafe to always ensure flow to the engine. Pressure comp flow controls are constant at all viscosities.