[Toobuilder]

With the results of the recent oil filter study now firmly under discussion, it feels like there is an emerging desire to branch out from even the traditional media filters and look to the auto/industrial world for “better”. While that is an admirable goal, it seems it’s a logical next step for that thread - this thread is the NEXT step beyond, so I thought I’d break off to keep that one on track.

Note: In this context, Bypass Filtration is the scheme where the oil pressure supply is tapped off and a small percentage of the oil is forced through an extremely fine filter media and returned, clean, directly to the crankcase. This oil filtration is too slow to feed the bearings directly, but eventually cleans all the oil in the sump.

Bypass filtration has an almost mythical reputation to actively purify oil while still in the crankcase. Its proponents will passionately argue the virtues of this scheme with religious fervor. On paper, it looks great - you run your crankcase oil through an incredibly fine filter that strips out every hard particle that can wedge in an oiled, sliding surface. And the dirtier the filter gets, the more effective it becomes. The heavy duty diesel truck and heavy equipment industry has many of the most vocal proponents, and since their big bore, large clearance, dirty fuel powerplants are a reasonable analog to our own, maybe it’s time to take a look. Since we know that extraordinary claims require extraordinary evidence, is anyone aware of any HARD DATA that would support widespread adoption of the bypass scheme on our engines? The primary benefit of the heavy mover crowd seems to be the vastly increased oil change intervals - in some cases, to indefinite. Many of these guys simply change the pressure filter and keep topping off the crankcase as required. One of the bypass filter manufacturers claims a life of 2000 (yes, two THOUSAND) hours before replacement is required. I am aware that bypass filtration is used on some airplanes - a buddy has a Franz system on his turbo Bonanza - but the standard oil change interval is maintained in his case.

So, anyone have any real data these systems work as claimed, and if so, does that open up any practical benefits for the Lycoming driver?

 

[rv8ch]

My experience is that I bought a Franz system, and decided not to install it as I felt the number of additional fittings and paths for my oil to escape increased the risk of a total engine failure more than the benefits of cleaner oil. This is based on my skills and understanding of the Lycoming engine and the Franz bypass oil filter system. Someone with more experience, a better test bed, and more time to invest testing might want to install such a system.

As an aside, I changed my oil yesterday with far less than 50 hours, since I hit the 4 month magic number. The oil still looked very clean, and the only thing in the filter was a bit of carbon. If I had a bypass filtration system, my oil might have been a tad bit cleaner, but I'd still be required to change it. For those of you who can fly as long as you want on the oil, a system like this might be interesting. One thought I had was is it possible that the filtration is "too good", and will filter out important oil additives? Or could there be another undesirable unintended consequence of running oil through a very fine filtration system?

Looking forward to a good discussion!

 

[Freemasm]

Kidney loops are typically utilized when the system proper is not a full flow system. Our oil systems are basically full flow minus the very small amount byoassed for system pressure regulation. Application here would be very much down the diminished returns asymptote; plus the downsides of more weight, more complexity, more FMEA points of course.

We design kidney loops into systems like hydraulic systems where the flow can be wildly variable. Hydraulic actuators have very low flows (through the servo valves) when actuators are not in motion; then, can exceed the pump’s output when slewed at high rates/frequencies.

A kidney loop is a good way of helping guarantee the oil is clean when suddenly needed in the primary loop and before it hits any system or “last chance” filter.

Low flow means low dPs across filter elements so no element condition indication/alarms. A sudden flow demand can create actuator stall, position mis-match, system trip before or consequently with the primary loop filter alarm.

Lots of words. I have a very hard time imagining a measurable benefit in most ICE lubrication system being what they are. Sure, finer filtration and more filtration cycles is never bad but see the previous diminished returns statement. All that said, people who have convinced themselves of a benefit post install aren’t going to change their mind.

 

[Toobuilder]

Sure, finer filtration and more filtration cycles is never bad but see the previous diminished returns statement...

Diminished returns, a positive ROI, or a favorable Cost/Benefit analysis all require the performance data in hand first. Once you validate the performance of the system under study, THEN you can decide if it's "worth it".

The performance "claims" indicate that the filter will "...efficiently remove contaminants (98.7 percent efficiency) down to 2 microns...". At face value, a full time "engine oil cleaning machine" that pulls out all the junk down to 2 microns seems like a very good thing. It's like putting new oil in the crankcase every 2 hours, or so it would seem. If this is true (and that remains to be verified in this thread), so what? What does that buy us in our environment? Do aviation engines build up some other contaminant or undergo chemical transformation that drives an oil change regardless of how "clean" a bypass filter maintains the crankcase oil?

 

[skylor]

Diminished returns, a positive ROI, or a favorable Cost/Benefit analysis all require the performance data in hand first. Once you validate the performance of the system under study, THEN you can decide if it's "worth it".

The performance "claims" indicate that the filter will "...efficiently remove contaminants (98.7 percent efficiency) down to 2 microns...". At face value, a full time "engine oil cleaning machine" that pulls out all the junk down to 2 microns seems like a very good thing. It's like putting new oil in the crankcase every 2 hours, or so it would seem. If this is true (and that remains to be verified in this thread), so what? What does that buy us in our environment? Do aviation engines build up some other contaminant or undergo chemical transformation that drives an oil change regardless of how "clean" a bypass filter maintains the crankcase oil?

The real question in my mind is will the bypass filtration system filter enough oil to remove that contaminants faster than they are being produced by the engine. It may remove 98.7 percent of the particulates of the oil that passes through it, but I suspect the total volumetric flow of the oil through the bypass system is very small compared to the oil flow of the whole oil system, so that 98.7 percent efficiency may really only be 5% efficiency or less . It sounds like a fair amount of extra complexity and weight added to the oil system with likely very little real benefit.

Skylor

 

[gasman]

A bypass filter could be easily connected to an altered sump drain and returned to the motor by way of filler neck.
It could filter as fine and as long as you want with no issues during flight.

If there is a test to see what has been stripped from or added to the oil, it would be interesting to see the useful service life.

 

[rockyfatcat]

The Frantz filter used to be great! They don’t make toilet paper rolls that size anymore. (The cardboard tube). The Frantz system would pull a fraction of the total flow and filter in down to 2 microns by forcing it through a roll of toilet paper and returning it to the system.

In my opinion, in an aircraft there are too many possible failure points. I have used the Frantz system in my cars, and I have had them fail to seal properly. BIG MESS!

A bypass filtration system (like the Frantz) has the potential to be a better way to keep your oil clean. I would be interested if there was a modern incarnation of the toilet paper filter that had an aircraft grade system of sealing it up that was bulletproof.

 

[Toobuilder]

The real question in my mind is will the bypass filtration system filter enough oil to remove that contaminants faster than they are being produced by the engine. It may remove 98.7 percent of the particulates of the oil that passes through it, but I suspect the total volumetric flow of the oil through the bypass system is very small compared to the oil flow of the whole oil system, so that 98.7 percent efficiency may really only be 5% efficiency or less . It sounds like a fair amount of extra complexity and weight added to the oil system with likely very little real benefit.

Skylor

I have read they flow .5 GPM, so 30 gallons per hour. So in theory, a typical cross country flight will see the entire oil supply "washed" several times.

 

[Toobuilder]

A bypass filtration system (like the Frantz) has the potential to be a better way to keep your oil clean. I would be interested if there was a modern incarnation of the toilet paper filter that had an aircraft grade system of sealing it up that was bulletproof.

Amsoil makes a spin on filter. I have one of these that I intended to try on the Rocket, but have not done so yet

 

[Freemasm]

Diminished returns, a positive ROI, or a favorable Cost/Benefit analysis all require the performance data in hand first. Once you validate the performance of the system under study, THEN you can decide if it's "worth it".

The performance "claims" indicate that the filter will "...efficiently remove contaminants (98.7 percent efficiency) down to 2 microns...". At face value, a full time "engine oil cleaning machine" that pulls out all the junk down to 2 microns seems like a very good thing. It's like putting new oil in the crankcase every 2 hours, or so it would seem. If this is true (and that remains to be verified in this thread), so what? What does that buy us in our environment? Do aviation engines build up some other contaminant or undergo chemical transformation that drives an oil change regardless of how "clean" a bypass filter maintains the crankcase oil?

Honestly Mr. Robinson, I can't tell what side of the argument you're on. I'll stand by by previous statement; a kidney loop just isn't needed on a full flow system. I'll use the same words again, you're way into diminished returns at the cost of more weight and complexity.

I've designed a lot fluid systems for various turbines. They collectively have multiple millions of hours of validation/operation. We incorporated kidney loops into hyd systems for the reasons mentioned. We also incorporate them into steam turbine lube oil systems to dry the oil. Different approach/application but we get 100k hours from our bearings before OH with 25u/B=200 elements.

Franz filter systems utilize toilet paper rolls for filtration? Not for me in this lifetime but to each his own.

There is the point of "good enough." At some point other lifeing variables will become the limit, assuming they aren't already. More doesn't always equate to more-better. All of this is stuff you already know.

If this is a direction someone truly wants to pursue, a kidney loop just isn't a smart approach in my technical opinion.. Utilize a remote mount, main filter like other companies offer (Wolf?) if needed. Then source a main filter with the desired filtration rating plus increased surface area for both meeting existing dP limits and increased fouling margin for the expected increased fouling. Save the TP roll filters to dry your shop air

 

[ChiefPilot]

Honestly Mr. Robinson, I can't tell what side of the argument you're on. I'll stand by by previous statement; a kidney loop just isn't needed on a full flow system. I'll use the same words again, you're way into diminished returns at the cost of more weight and complexity.

Aside from that, the typical lycoming on an RV lives in a much, much cleaner environment than a piece of heavy equipment.

The hard data I looked at was the weight and size of the Franz system compared to not having it. Adding 8+ lbs (depending on installation specifics) forward of the firewall isn’t worth it for me.

 

[lr172]

Diminished returns, a positive ROI, or a favorable Cost/Benefit analysis all require the performance data in hand first. Once you validate the performance of the system under study, THEN you can decide if it's "worth it".

The performance "claims" indicate that the filter will "...efficiently remove contaminants (98.7 percent efficiency) down to 2 microns...". At face value, a full time "engine oil cleaning machine" that pulls out all the junk down to 2 microns seems like a very good thing. It's like putting new oil in the crankcase every 2 hours, or so it would seem. If this is true (and that remains to be verified in this thread), so what? What does that buy us in our environment? Do aviation engines build up some other contaminant or undergo chemical transformation that drives an oil change regardless of how "clean" a bypass filter maintains the crankcase oil?

what drives the frequent oil drain cycle in our engines is the fact that the lead blow-by particles load the oil to the level that it cannot hold any more in suspension and therefore we must refresh it or accept sludge build up. So, the question is, how large is a lead particle nad can one of these things filter them out. If not, we cannot extend our drain interval, at least not with 100LL. It was my understanding that soot and other carbon debris is the issue on diesels and believe that stuff is much larger particle size than the almost aerosolized lead we use in our fuel.

Larry

 

[Toobuilder]

It was my understanding that soot and other carbon debris is the issue on diesels and believe that stuff is much larger particle size than the almost aerosolized lead we use in our fuel.

Yes, this question is the philosophical genesis of this thread. These things are claimed to work wonders in diesel engines and diesels are very dirty with regards to combustion byproduct oil contamination just like our engines. The question remains, is it a different kind of “dirty”? And if so, is it different enough to render the bypass scheme ineffective?

if lead is the primary contaminant, and these filters let lead pass, then yes, their value is greatly diminished. If that’s the case though, then what about those who use unleaded?

 

[Toobuilder]

The hard data I looked at was the weight and size of the Franz system

Yep, the “kit” that is sold for automotive applications is not exactly weight conscious. That said, I have a scheme to integrate the Amsol spin on cartridge with very minimal added hardware. Essentially I’ll replace one of my magneto block off plates with a machined spin on adapter. The outlet of the filter exits into the accessory case (no hose or fittings) and it is fed from a short #4 line from a convenient pressure tap on the case - plumbed just like our oil pressure indication transducers. I think I can add the system for less than 1 pound penalty.

 

[DanH]

So, anyone have any real data these systems work as claimed, and if so, does that open up any practical benefits for the Lycoming driver?

Mike, the State of California conducted a long term study of higher efficiency oil filtration in an attempt to quantify extended oil change intervals for the state vehicle fleet. The study found extended intervals due to better filtration to be entirely valid, but the recommendations were impossible to implement statewide because local fleet managers refused to accept the results.

Sound familiar?

 

[ChiefPilot]

Mike, the State of California conducted a long term study of higher efficiency oil filtration in an attempt to quantify extended oil change intervals for the state vehicle fleet. The study found extended intervals due to better filtration to be entirely valid, but the recommendations were impossible to implement statewide because local fleet managers refused to accept the results.

Sound familiar?

Higher efficiency filtration is but one aspect of the bypass filter issue - and as Mike is trying to determine, one of unknown value at this time. Being fixated on a single axis of the subject (filtration efficiency beyond that of a high quality automotive filter, in this case) while ignoring the cost, complexity, weight gain, potential reliability, and so on of a system where the benefits cannot be quantified doesn't seem very ... efficient

 

[Toobuilder]

Honestly Mr. Robinson, I can't tell what side of the argument you're on. I'll stand by by previous statement; a kidney loop just isn't needed on a full flow system.

First off, I am not advocating for one "side" or another... there is no "argument". If the data can demonstrate there is no benefit to much cleaner crankcase oil or the benefit is so small that the system can't buy it's way onto the airplane on merit, then that information is gold. Bring it on! Unfortunately, there has been a lack of data supporting or discounting the performance claims. Lots of opinion, sure, but no data. The "other" oil filter thread smashed plenty of "opinion" and performance claims to bits with hard data, so this thread is simply looking for a similar level of certainty. While I am not discounting your professional experience, you are still only offering opinion.

This thread is looking for "data", not opinions. If data does not exist, then let's close the thread and move on.

 

[Toobuilder]

Higher efficiency filtration is but one aspect of the bypass filter issue - and as Mike is trying to determine, one of unknown value at this time. Being fixated on a single axis of the subject (filtration efficiency beyond that of a high quality automotive filter, in this case) while ignoring the cost, complexity, weight gain, potential reliability, and so on of a system where the benefits cannot be quantified doesn't seem very ... efficient

Since the cost, weight and other physical properties of the system can be directly measured or easily derived, then I don't see a need to even discuss them in this thread. It's the nebulous and sometimes fantastic performance claims that need to be validated, IMHO.

 

[ChiefPilot]

Since the cost, weight and other physical properties of the system can be directly measured or easily derived, then I don't see a need to even discuss them in this thread. It's the nebulous and sometimes fantastic performance claims that need to be validated, IMHO.

Sure they do. Unless you’re looking for something in the abstract, then implementation factors play a part. Why did the CA fleet managers not want to implemen bypass filtration schemes as Dan mentioned? Probably because there are other factors at play.

There‘s someone with some professional experience saying these are a bad idea for our application, and there is a definite cost/weight/complexity disadvantage. But I get the quest for actual data. Hopefully you’ll find some.

 

[Toobuilder]

But I get the quest for actual data. Hopefully you’ll find some.

That's all I'm looking for in this thread. Does not seem like a big ask, but seems to be.

 

[DanH]

Why did the CA fleet managers not want to implement bypass filtration schemes as Dan mentioned? Probably because there are other factors at play.

That's one of the interesting observations. They were surveyed twice, before and after the demonstration phase of the program. Given actual data, many original objections were dropped...to be replaced by new ones.

Certainly some concerns were valid. Others simply challenged settled belief. And "cost" depends a lot on what is valued. Here the state agency was at least partially driven by environmental concerns for waste oil. Another agency may not share the concern, or already has a solution, so that point would not be as valued. "To each his own!" said the lady who kissed the cow...

But I get the quest for actual data. Hopefully you’ll find some.

Here you go Mike. https://www.danhorton.net/VAF/Filter Test Results/California HE Filter Study.pdf

 

[rocketbob]

A while back I firewall mounted a very low cost bypass filtration setup on my rocket (not yet flying.).

Mount:

OB1305 - Baldwin - Lube Filter Bases | Baldwin

Baldwin lube filter bases may be used to convert an application to spin-on style filters or to add by-pass filtration.

ph.baldwinfilters.com

Filter:

B164 - Baldwin - Spin-on Lube Filters | Baldwin

Baldwin spin-on lube filters protect your engine from wear particles that can otherwise lead to premature parts failure.

ph.baldwinfilters.com

B164 filters are about $14 on Amazon. Rated 2 microns at 50%.

 

[Freemasm]

First off, I am not advocating for one "side" or another... there is no "argument". If the data can demonstrate there is no benefit to much cleaner crankcase oil or the benefit is so small that the system can't buy it's way onto the airplane on merit, then that information is gold. Bring it on! Unfortunately, there has been a lack of data supporting or discounting the performance claims. Lots of opinion, sure, but no data. The "other" oil filter thread smashed plenty of "opinion" and performance claims to bits with hard data, so this thread is simply looking for a similar level of certainty. While I am not discounting your professional experience, you are still only offering opinion.

This thread is looking for "data", not opinions. If data does not exist, then let's close the thread and move on.

I'll shorten my stance then. I don't have the data you seek obviously, but my main point regards your proposed bypass filtration approach. It truly makes no sense here. I'll state again in short summary, you're better off applying better filtration to the main circuit (with aforementioned considerations) versus a kidney loop here. Sorry for not answering part of your question.

 

[Jjackh10]

The hard data for filtration performance and benefit analysis exists. But unfortunately might not be shared readily. As mentioned heavy industry has put a ton of research into this. In my experience, usually, the chosen method is periodic filtering. This is accomplished by attaching a "filter cart" to the machine (turbines, gearboxes, 340 ton haul trucks, etc), and circulating the oil through a series of separators and filters. These "filter carts" range from trailer mounted units to a handcart with filters and a little pump mounted.

A pretty nice portable "cart" could be built very inexpensively. This would avoid some of the concerns with an airframe installed system. I'd think it would permit aviation specific data to be collected reasonably affordably as well. Maybe help determine the value of a mounted system? Plus it would be a great excuse to go to the hangar on a rainy day or skip cutting the grass. Sorry hunny, science!

 

[Toobuilder]

Here you go Mike.

Thanks for that Dan. Sounds like the marketing propaganda from the manufacturers and the fervor of the true believers in the consumer group is largely justified. That’s a valuable data point.

I did not read the whole report yet but did pick up on 2 key elements of interest - first, the oil analysis results were different based on the engine types diesel, gasoline and CNG. All did better with the bypass, but the fuel type variation still leaves a big open hole for data concerning our use of leaded fuel. The second point was the dismissal of the common concerns that the bypass filtration was so fine as to “strip the additives out” of the oil during the cleaning process.

So in my mind the bypass scheme has a confirmed ability to cleanse sump oil in-situ, it does not strip additives, but the use of leaded fuel is still a big question. Without exploring the leaded fuel variable more I can’t think of a way to quantify the benefit, but I’d be hard pressed to think of a reason the presence of a bypass filter on an airplane would degrade oil.

And at the risk of getting into a completely unnecessary debate over “risk”, I am confident the bypass system can be installed IAW accepted aviation standards and will result in a system that exceeds or equals the safety relative to other commonly used aviation accessories such as remote mount oil filters, oil coolers, smoke systems or inverted oil systems.

 

[Jjackh10]

Thanks for that Dan. Sounds like the marketing propaganda from the manufacturers and the fervor of the true believers in the consumer group is largely justified. That’s a valuable data point.

I did not read the whole report yet but did pick up on 2 key elements of interest - first, the oil analysis results were different based on the engine types diesel, gasoline and CNG. All did better with the bypass, but the fuel type variation still leaves a big open hole for data concerning our use of leaded fuel. The second point was the dismissal of the common concerns that the bypass filtration was so fine as to “strip the additives out” of the oil during the cleaning process.

So in my mind the bypass scheme has a confirmed ability to cleanse sump oil in-situ, it does not strip additives, but the use of leaded fuel is still a big question. Without exploring the leaded fuel variable more I can’t think of a way to quantify the benefit, but I’d be hard pressed to think of a reason the presence of a bypass filter on an airplane would degrade oil.

And at the risk of getting into a completely unnecessary debate over “risk”, I am confident the bypass system can be installed IAW accepted aviation standards and will result in a system that exceeds or equals the safety relative to other commonly used aviation accessories such as remote mount oil filters, oil coolers, smoke systems or inverted oil systems.

I think the benefit could primarily be quantified by calculating the reduced count of oil changes. Reduced oil changes, resulting in reduced downtime, has been the primary benefit in heavy industry. In fixed equipment the "filter cart" method is performed online. And on mobile equipment its a quick pit stop. There is probably some improvement in engine life but I suspect it wouldn't be measurable outside of a lab where all the other variables are controlled (temperature, humidity, fuel quality, operating profiles and such).

My TLAR guess is that a filter cart might pay for itself, might.

 

[Jjackh10]

I haven't seen an oil analysis from a lycoming at oil change. Sincere question, as much as they consume and as often as it's changed is it really that bad?

 

[DanH]

I did not read the whole report yet but did pick up on 2 key elements of interest - first, the oil analysis results were different based on the engine types diesel, gasoline and CNG. All did better with the bypass, but the fuel type variation still leaves a big open hole for data concerning our use of leaded fuel.

I don't think so. I just thought it was a nice sampling of usage, not so much fuel type.

For example, there were a bunch of Cavaliers, which would be low budget state pool floggers, some driven by the meek, others by madmen. Lots of data scatter, and I suspect a lot of difference in engine condition, station to station.

There were forest fire crew trucks. Poster children for "Used hard in dirty air on dirt roads".

Now look at the CNG busses. Same routes every day, same garage every night, professional full time drivers. No dirt roads, no forest fires. Nice tight graphs.

Last, old prison buses and 15 passenger vans, apparently mixed GMC and Ford. Lots of data scatter. No surprise...hardly a homogenous group.

Leaded fuel? Do the same oil monitoring, track TBN, viscosity, and solubles.

 

[airguy]

I haven't seen an oil analysis from a lycoming at oil change. Sincere question, as much as they consume and as often as it's changed is it really that bad?

Consumption varies greatly - my IO360 burns a quart every 20-25 hours, and I know a few others that are better than that. I only add one quart between oil changes.

 

[ERJDriver]

I've got a bypass on my diesel truck, 2 micron Baldwin filter. Cheap. Change every 2 or 3 oil changes.

Put one on my dad's excursion and it's got 680k on it now. 20k oil change intervals.

Would love to see one on a plane

 

[Toobuilder]

It truly makes no sense here. I'll state again in short summary, you're better off applying better filtration to the main circuit (with aforementioned considerations) versus a kidney loop here.

This is a compelling statement. I’ve been turning it over in my head for a few days and considering your conviction I’d like to pick at your reasoning here.

I assume that we are discussing the removal of abrasive particulates when you mention “…better filtration to the main circuit”, as opposed to acid build up or other “non mechanical” aspect of filtration. If that is the case, then it seems that we are pretty close to the limits we can get with ”full flow” filtration because of the balance between adequate filtration and required flow rate. We can agree that there are some high performance filter media out there that apparently improve the consistent capture of smaller particulates AND still flow enough oil to keep the bearings alive, but can we also agree that even the best possible full flow filter will not even approach the capture performance of the typical bypass filter? (in theory, I suppose you COULD have a full flow filter that cleans down to 2 microns and feeds the GPM requirements of the Lycoming oil pump, but I’ll bet it would be the size of a household trash can.). That said, given the choice to pump from a sump full of particulate rich oil and cleaning down to say, 15 microns before feeding it to the bearings (this is your “better filtration“ approach), OR drawing from a sump that contains only particulates no larger than 2 microns prior to the full flow filter, it seems fairly obvious to me that drawing from cleaner oil to begin with is the best approach. After all, if the oil is clean enough to begin with, the full flow filter is just along for the ride - it’s not “filtering” anything, because there is nothing in the oil large enough for it to catch.

 

[DanH]

Just an observation....
As the primary filter accumulates dirt, efficiency goes down when velocity through the remaining pore area rises. I suspect it's one reason why the low velocity bypass filters can retain smaller particles.

 

[Toobuilder]

Well, that and the fact that the pore size is incredibly small and super high density. After all, one of the best known bypass filters uses a whole roll of toilet paper for media. Can you imagine trying to force cold 50wt oil through a roll of Charmin at 10 GPM? Ouch!

You do bring up an interesting point though…. Cleaner supply oil delays the onset of the main filter efficiency drop off. Or said another way, a bypass filter has the potential to make the pressure filter remain “better” for “longer”?

 

[Freemasm]

#

This is a compelling statement. I’ve been turning it over in my head for a few days and considering your conviction I’d like to pick at your reasoning here.

I assume that we are discussing the removal of abrasive particulates when you mention “…better filtration to the main circuit”, as opposed to acid build up or other “non mechanical” aspect of filtration. If that is the case, then it seems that we are pretty close to the limits we can get with ”full flow” filtration because of the balance between adequate filtration and required flow rate. We can agree that there are some high performance filter media out there that apparently improve the consistent capture of smaller particulates AND still flow enough oil to keep the bearings alive, but can we also agree that even the best possible full flow filter will not even approach the capture performance of the typical bypass filter? (in theory, I suppose you COULD have a full flow filter that cleans down to 2 microns and feeds the GPM requirements of the Lycoming oil pump, but I’ll bet it would be the size of a household trash can.). That said, given the choice to pump from a sump full of particulate rich oil and cleaning down to say, 15 microns before feeding it to the bearings (this is your “better filtration“ approach), OR drawing from a sump that contains only particulates no larger than 2 microns prior to the full flow filter, it seems fairly obvious to me that drawing from cleaner oil to begin with is the best approach. After all, if the oil is clean enough to begin with, the full flow filter is just along for the ride - it’s not “filtering” anything, because there is nothing in the oil large enough for it to catch.

Don't have time for a complete response. I'm between mtgs and the next one will take me into the evening.

Previously stated:
- Finer filtration is better. Few would argue the contrary.
- A full flow system doesn't need a kidney loop.
- The previous adds weight, complexity, and additional FMEA points.
- An element with finer filtration that meets existing dP requirements and fouling margin will need more surface area hence the remote mount comment. Do our machines really create that much DOD between filter changes? BTW, as a Rocket owner, you surely don't have room for ANYTHING else under your cowl do you?

Additional points:
- I did go look at the Frantz website. Their system is an extraction/branch type. Do you really want to take primary flow from your lube circuit? The circuit flow is basically fixed for any given engine RPM.
- I do like jjackh10's idea of a filter cart and will bump that around in my head. That could be very effective with the right extraction/return points and done while the oil is still hot. The way my build is progressing, ain't gonna matter to me.
- Yes you'd like to start with clean oil but some (most?) of the FOD/DOD had to travel through the system at least once. Probably just a minor contributor.

Ultimate solution?
A filter element with two stage filtration; say 25u and 10u or whatever. Each stage with a dedicated bypass. If the second stage (finer) BP lifts, you're really in no different conditions than any current offering. I'd buy that.

Times up.

 

[Toobuilder]

…A full flow system doesn't need a kidney loop…

I’m not trying to be argumentative here but you have stated this several times without articulating “why”…. You are obviously passionate about this particular aspect so I continue to be interested in the “why” behind your perspective.

My response to this is ”Clean oil does not need full flow filtration”.

A for the moment let’s forget about the cost, packaging or weight…. Those are well known. Those have to be compared with the performance improvement (if any) to drive a CBA. So far we only have one half of the data needed to perform a CBA. And if ANY weight, cost, or reliability detriment is unacceptable on our airplanes then we need to forgo paint, interior, sound deadener, inverted oil, smoke systems, and any other number of “non essential” items. But this is VAF, and we all assign value differently. Can we focus on “filter performance” for this first step? Once we establish performance, then I’m happy to start a new thread and we can debate CBA criteria until the cows come home.

 

[Snowflake]

With a quick-drain on the bottom of your sump, and a return hose into the filler neck, one could plug in a bypass filter cart after each flight and put it on a timer to run while the oil cools. While it's still warm, it'll run easily and filter niicely. I wonder if this would be the ideal solution? And further, if you were doing this after every flight, could you reduce weight further by capping off the oil filter port entirely? Just start every flight with freshened oil?

 

[Toobuilder]

if you were doing this after every flight, could you reduce weight further by capping off the oil filter port entirely? Just start every flight with freshened oil?

Interesting thought exercise, but for this to be practical you would still want some form of screen upstream of the bearings to catch those chunks that make it past the oil pump suction screen. The engine does produce those random harmful bits as a function of operation so the oil system needs to accommodate debris generated AFTER the post flight purification process you describe.

 

[Jjackh10]

I’m not trying to be argumentative here but you have stated this several times without articulating “why”…. You are obviously passionate about this particular aspect so I continue to be interested in the “why” behind your perspective.

My response to this is ”Clean oil does not need full flow filtration”.

A for the moment let’s forget about the cost, packaging or weight…. Those are well known. Those have to be compared with the performance improvement (if any) to drive a CBA. So far we only have one half of the data needed to perform a CBA. And if ANY weight, cost, or reliability detriment is unacceptable on our airplanes then we need to forgo paint, interior, sound deadener, inverted oil, smoke systems, and any other number of “non essential” items. But this is VAF, and we all assign value differently. Can we focus on “filter performance” for this first step? Once we establish performance, then I’m happy to start a new thread and we can debate CBA criteria until the cows come home.

Maybe I'm too simple minded

This is a compelling statement. I’ve been turning it over in my head for a few days and considering your conviction I’d like to pick at your reasoning here.

I assume that we are discussing the removal of abrasive particulates when you mention “…better filtration to the main circuit”, as opposed to acid build up or other “non mechanical” aspect of filtration. If that is the case, then it seems that we are pretty close to the limits we can get with ”full flow” filtration because of the balance between adequate filtration and required flow rate. We can agree that there are some high performance filter media out there that apparently improve the consistent capture of smaller particulates AND still flow enough oil to keep the bearings alive, but can we also agree that even the best possible full flow filter will not even approach the capture performance of the typical bypass filter? (in theory, I suppose you COULD have a full flow filter that cleans down to 2 microns and feeds the GPM requirements of the Lycoming oil pump, but I’ll bet it would be the size of a household trash can.). That said, given the choice to pump from a sump full of particulate rich oil and cleaning down to say, 15 microns before feeding it to the bearings (this is your “better filtration“ approach), OR drawing from a sump that contains only particulates no larger than 2 microns prior to the full flow filter, it seems fairly obvious to me that drawing from cleaner oil to begin with is the best approach. After all, if the oil is clean enough to begin with, the full flow filter is just along for the ride - it’s not “filtering” anything, because there is nothing in the oil large enough for it to catch.

Maybe I'm thinking too simple minded but I'm struggling to understand this. If a 2 micron filter cleaning a bleed stream would be effective why would you have a 15 micron full stream filter? If the low flow 2 micron filter can't clean as fast as it's getting dirty then what use is it?

 

[Toobuilder]

...With a quick-drain on the bottom of your sump, and a return hose into the filler neck...

I've given this a fair amount of thought and one very simple concept is to machine a spin on adapter that mounts in place of one of my magneto cover plates. Little more than a flat plate that has a nipple on it, it's fed with a single #4 line from the nearest oil galley port and returns through the cover into the accessory case. Smaller overall than the magneto it replaced, and based on the raw materials I've collected, I can do it for 1 pound or less.

 

[Jjackh10]

With a quick-drain on the bottom of your sump, and a return hose into the filler neck, one could plug in a bypass filter cart after each flight and put it on a timer to run while the oil cools. While it's still warm, it'll run easily and filter niicely. I wonder if this would be the ideal solution? And further, if you were doing this after every flight, could you reduce weight further by capping off the oil filter port entirely? Just start every flight with freshened oil?

I'd think that would be a plausible option. This discussion is interesting to me as an academic discussion. But I do doubt the value beyond increased oil change intervals. My air cooled, constant load, harsh environment, lawn mower still fires right up after 8 years. Despite me only looking at the dipstick half a dozen times. Then again oil changes are expensive. $800 dollars or so into a filter cart could probably pay for itself. Especially if shared between other toys or friends.

 

[Jjackh10]

I've given this a fair amount of thought and one very simple concept is to machine a spin on adapter that mounts in place of one of my magneto cover plates. Little more than a flat plate that has a nipple on it, it's fed with a single #4 line from the nearest oil galley port and returns through the cover into the accessory case. Smaller overall than the magneto it replaced, and based on the raw materials I've collected, I can do it for 1 pound or less.

Just a note if y'all do build some filter carts. We used positive connection mechanism's (air hose quick connects, or camlocks, or threaded connections) on both the supply and return lines. And mounted corresponding dead end connections on the cart. It helped keep the connections clean and the drip trails to a minimum.

 

[Toobuilder]

Maybe I'm too simple minded

Maybe I'm thinking too simple minded but I'm struggling to understand this. If a 2 micron filter cleaning a bleed stream would be effective why would you have a 15 micron full stream filter? If the low flow 2 micron filter can't clean as fast as it's getting dirty then what use is it?

Because there are two conditions you need to address. One is the acute production of debris that can damage the bearings on the first pass. That's why there is a pressure screen in the first place. The second is the long term accumulation of particulates that he full flow lets pass every time until there is so much of it that the oil becomes "dirty". The original screen and later the spin on filter address the acute, and an oil change addresses the "dirty". A bypass filter aims to delay both conditions.

 

[Toobuilder]

Just a note if y'all do build some filter carts.

To be clear (since you quoted me), the concept I described is hard mounted and plumbed, and only operates if the propeller is turning. There is no cart or pilot action required post operation.

 

[Jjackh10]

To be clear (since you quoted me), the concept I described is hard mounted and plumbed, and only operates if the propeller is turning. There is no cart or pilot action required post operation.

All good, I got confused reading through the posts haha.

 

[gasman]

With a quick-drain on the bottom of your sump, and a return hose into the filler neck, one could plug in a bypass filter cart after each flight and put it on a timer to run while the oil cools. While it's still warm, it'll run easily and filter niicely. I wonder if this would be the ideal solution? And further, if you were doing this after every flight, could you reduce weight further by capping off the oil filter port entirely? Just start every flight with freshened oil?

This.... is what I was talking about in post #6. You do it in the hangar, after a flight and risk nothing during flight without adding any weight to the aircraft.

I plan to use two tubes that are passed down the filler neck. One touches the bottom, cut on a 45. The other tube only goes 1/2 way down the neck. Open the oil door, remove the dip stick and slide in the tubes to the filter and flip a switch and use a timer for the amount desired.... Maybe the same as the last flight.

I have a few gallons of used oil to test the system and the filter media choices.

 

[Toobuilder]

I plan to use two tubes that are passed down the filler neck…

I wonder if this method will capture “all“ of the oil in the sump during the recycle process? While the proposed method will have no negative impact other than the potential to introduce additional contamination during the hose insertion process, I also question the effectiveness of cleaning the oil while it is stagnant, without a complete drain? I know both methods are widely used in the industry, but it feels like the in-situ method has a better chance of catching more of the crud you are trying to filter out.

 

[Freemasm]

This.... is what I was talking about in post #6. You do it in the hangar, after a flight and risk nothing during flight without adding any weight to the aircraft.

I plan to use two tubes that are passed down the filler neck. One touches the bottom, cut on a 45. The other tube only goes 1/2 way down the neck. Open the oil door, remove the dip stick and slide in the tubes to the filter and flip a switch and use a timer for the amount desired.... Maybe the same as the last flight.

I have a few gallons of used oil to test the system and the filter media choices.

This idea has been bumping around in my head since first mentioned. Could easily adapt it into a real kidney loop with flow through some type of pH conditioner, dehydrator, etc. before the final filtration to help maintain the oil's properties. The two tube/filler neck idea would work better for the former (conditioning) as it would have the benefit of equilibrium to affect oil that was not processed through the loop. The latter would rely on dilution so the bulk oil u level would never be achieved.

@ Several references. Summarizing = "Why does clean oil need to be filtered?" It doesn't stay clean; hence my previous DOD reference (Domestic Object Debris/Damage) for those never baptized in the church of aerospace. Sorry for the reference. Look at some of the opened filter element pix in this forum. Some of that would cause pretty extensive wear being recirculated even in a short flight

I’m not trying to be argumentative here but you have stated this several times without articulating “why”…. You are obviously passionate about this particular aspect so I continue to be interested in the “why” behind your perspective.

My response to this is ”Clean oil does not need full flow filtration”.

A for the moment let’s forget about the cost, packaging or weight…. Those are well known. Those have to be compared with the performance improvement (if any) to drive a CBA. So far we only have one half of the data needed to perform a CBA. And if ANY weight, cost, or reliability detriment is unacceptable on our airplanes then we need to forgo paint, interior, sound deadener, inverted oil, smoke systems, and any other number of “non essential” items. But this is VAF, and we all assign value differently. Can we focus on “filter performance” for this first step? Once we establish performance, then I’m happy to start a new thread and we can debate CBA criteria until the cows come home.

You're a smart guy, Sir. Being in Mojave, I assume you have an aerospace job. If all of a commodity is being treated to the level you desire, there's no reason to treat some of it in a bypass loop. Do as you wish and I'm rooting for the outcome you're seeking. A couple of things for you're consideration and I'm done here:

- I'd do a lot of inquiry into the required oil flow for your particular powerplant. As mentioned, the flow is basically constant for a given engine RPM. I'm assuming that oil system flow is similar to the other design parameters related to our machines versus ground dwelling types; the design margins will be much smaller/less conservation. Also, the losses are related to the square of the flow rate so the portioned that gets bypassed will increase at lower RPM. Don't know if that's good or bad but I'll assume that idle speed is the most critical resign point. Before I extracted any primary flow for a proposed bypass, I'd try to get very comfortable knowing that I hadn't swapped one lifeing parameter for another.

- Don't limit yourself to ICE oil filters in your search. Hydraulic systems require much finer filtration; servovalves being the limiting component. Their range of flow design points will also go much lower.

Drift = I got to spend a little time in Moog in NY state for both my aerospace and power industry careers. Dealt with some flat-out stud engineers up there. Anyway, the servovalve motors have very tight clearances, in the tens of thou clearances for their more specialized apps. The related spool which actually controls the actuator flow was even tighter, numbers not shared with me. If you extracted one from the servovalve housing and let it warm up in your hand, it wouldn't go back the bore. Not too much impresses me anymore. Hadn't thought about it in a long time but that memory still makes an impression on me.

Design safe, build safe, fly safe, Sir.

 

[Toobuilder]

If all of a commodity is being treated to the level you desire, there's no reason to treat some of it in a bypass loop...

The issue this secondary filter process is trying to address is the fact that the packaging requirements of an aircraft engine will not allow the full flow filter to get down as fine as desired. No way to feed bearings enough oil while going through a 2 micron filter. Like most things in aviation, the full flow is a filter is a design compromise trying to achieve acceptable filtration at acceptable flow rate. If there was a full flow filter that could deliver enough oil to support the bearings AND was 2 microns, everyone would use it. The bypass filter is a method to achieve the overall effect of 2 micron clean oil without impacting the primary oiling system.

And speaking of impacting the primary oiling system…

I'd do a lot of inquiry into the required oil flow for your particular powerplant.

The bypass system bleeds oil through a 0.050 orifice. The filter could be fed with a #2 AN hose and it would still be oversized. Admittedly, this is a slight tax on the oiling system, but hardly noticeable. Far less than the tax of piston oil squirters anyway. And let’s also not forget that some of these bypass systems are STC’d for installation on aircraft. It’s not a radical concept.

 

[Snowflake]

Interesting thought exercise, but for this to be practical you would still want some form of screen upstream of the bearings to catch those chunks that make it past the oil pump suction screen. The engine does produce those random harmful bits as a function of operation so the oil system needs to accommodate debris generated AFTER the post flight purification process you describe.

Well, you do still have the oil screen in the sump. It's a coarse filter, but would catch the big stuff.

The question is, does an average engine create enough wear particles during one flight (or day's flying) to cause rapid degradation during that flight? I would suspect not, as the engines only came with the oil screen originally. So a filter cart once a day would be like flying an engine that had only an oil screen, but effectively with a fresh oil change after every flight.

 

[Toobuilder]

Well, you do still have the oil screen in the sump. It's a coarse filter, but would catch the big stuff.

The question is, does an average engine create enough wear particles during one flight (or day's flying) to cause rapid degradation during that flight? I would suspect not, as the engines only came with the oil screen originally. So a filter cart once a day would be like flying an engine that had only an oil screen, but effectively with a fresh oil change after every flight.

The suction screen protects the oil pump, and the pressure screen protects the bearings. The suction screen is a rock catcher, the pressure screen catches pebbles. Both of these are addressing the acute issues like the “DOD” (Domestic object debris) referenced earlier. The bypass cleansing is what keeps the oil heathy longer and maintains the ability to perform its primary function to “clean, cool, and lubricate” the engine internals.

if one was looking to reduce the weight of the filter, then going back to the traditional oil screen would still be a minimum requirement in my mind. Then at least you would “do no harm” compared to the original design of the engine oil system.

With THAT said (and this is just a thought exercise), then weight reduction can be had with a smaller filter. I did fly several oil changes with a NAPA 1042 can on my 540 without any apparent issue. And this is a filter that is smaller than your fist. It’s tiny.