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Mike Busch's thoughts on oil separators

Seems what he doesn't like is the idea of putting the "effluent" back into the engine. If I understand the Anti Splat device correctly the effluent gets burned through the exhaust. The Andair device comes with a little container that can be installed where it is accessible without decowling, and the "effluent" goes there. This is what I have installed on my Rocket - not yet flying (awaiting final inspection).
 
I'm in the process of writing an article regarding air / oil separators for publication in a future issue of KitPlanes.

My research indicates that there are as many opinions on using an air oil separator as there are people.

What I'm struggling with is finding true facts on if they are a good or bad thing.

Pouring a bunch of stuff on the ground doesn't neccissarly mean anything and based on the design of the separator, that water (?) could be burned off, captured, or returned to the engine.

One person I interviewed mentioned that there are a number of certified airplanes with separators installed at the factor and there are STC's to retrofit them. If they were so bad, why would this be allowed? - Interesting point.
 
I put an air/oil separator on the Lycosaur O-540 in our last airplane. We installed it when we rebuilt the engine, because I liked the idea of having a clean belly.

The old graybeards on the field scoffed at me for doing so. One of them laughed and said "Son, your aircooled engine has 15 different potential sources of oil on the belly. You just spent a lot of money to cure one of them."

At the time I thought "What a rube!". However, in retrospect I have to admit that he was right. As the engine aged (we flew it for 12 years and 1400 hours) it sprouted a drip here, and a seep there, and -- like an old Harley, it began to mark its territory. The expensive air/oil separator, once effective at keeping the belly clean, ultimately became something of a joke.

I'm not planning to put one on our -8A.
 
I "Son, your aircooled engine has 15 different potential sources of oil on the belly. You just spent a lot of money to cure one of them."

Just a thought here, but I wonder....................

How much would the other 14 locations leak if the crankcase was under vacuum as happens with the vent line attached to the exhaust ???
 
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I installed an AS oil sep on my 7 20hrs ago and the oil on the belly is no longer a problem. About the stuff that is returned to the engine---A friend installed a reservoir to catch the return oil out of the separator on his lycoming and it amounted to several table spoon fulls between oil changes and did not look contaminated (at least not like the video showed). I'm sure it was to an extent but looked harmless to a mechanic of 50 years. I am happier with the separator than not and will leave it on. Just sharing an experience. :) Larry
 
We have an Andair separator with the extra gob catcher.

It was set too low initially - I just used someone elses placement. We got lots of oily belly when doing hammerheads and slow rolls.

After moving it higher, I can now do vne to vertical and stay until I run out of airspeed - not a drop.

The catcher gets cleaned every oil change and the milky stuff is thrown away.

Unless you put a half Raven or full system in, I really think that these do work well and certainly the Andair is beautifully crafted.
 
We have an Andair separator with the extra gob catcher.

It was set too low initially - I just used someone elses placement. We got lots of oily belly when doing hammerheads and slow rolls.

After moving it higher, I can now do vne to vertical and stay until I run out of airspeed - not a drop.

The catcher gets cleaned every oil change and the milky stuff is thrown away.

Unless you put a half Raven or full system in, I really think that these do work well and certainly the Andair is beautifully crafted.

Do you have a picture of your mount location or at least a good description of how high or where?

Thanks
 
After trying to make several different separators work properly, I just ended up running my breather tube into the exhaust pipe at 90 degrees and the excess burns off. I thought it was going to be an issue with extra suction pulling oil out of the crankcase, but I typically run about 25 hours before having to add another quart of oil, so I'm happy with this setup. No oil on belly.

Greg
 
Just got this article about oil separators in a Mike Busch newsletter I regularly receive. Seems he doesn't like them. Coincidentally, I happen to have an un-installed anti-splat kit ready to get put on. Hmm... Anyone know if the Anti-Splat ones mitigate any of the problems he mentions?

http://us5.campaign-archive1.com/?u=dfd69bf8f8fec1b9da00eedbd&id=bdba4d7067&e=1db3de8610

Hi Steve,
If you change your mind and want to sell,please let me know.
RHill
 
I'm in the process of writing an article regarding air / oil separators for publication in a future issue of KitPlanes.

My research indicates that there are as many opinions on using an air oil separator as there are people.

What I'm struggling with is finding true facts on if they are a good or bad thing.

Pouring a bunch of stuff on the ground doesn't neccissarly mean anything and based on the design of the separator, that water (?) could be burned off, captured, or returned to the engine.

One person I interviewed mentioned that there are a number of certified airplanes with separators installed at the factor and there are STC's to retrofit them. If they were so bad, why would this be allowed? - Interesting point.


I am one person that has run an oil separator that dumps back into the engine for more than 16-years. After 2,200 hours, I pulled the Superior Cylinders that I had as the valve guides were worn out. The cylinders still had the crosshatch and standard value choke in the barrel. I now have ECI cylinders. The head on one of the Superior Investment Cast cylinders had a crack around the valve seat that leaked between the seat and head. The cam looked good. I now have 2,850 hours on the engine. I fall in the category that no issues have been found or proved in my use of the Aircraft Spruce Homebuilders oil separator after 2,850 flying hours. I used AeroShell 15W-50 most of the first 2,200 hours. Have used Phillips X/C 20-50 almost exclusively since going to the ECI (steel) Titan cylinders.

BTW, the engine I have was made in 1961 and now has total time of over 5,700 hours. It had a wet vacuum pump that used an oil separator that put the waste oil from the wet vacuum pump back into the engine when it was removed from a certificated aircraft. This is not the same thing as the crankcase vent that now goes into the inexpensive Aircraft Spruce Homebuilders special oil separator.
 
Just got this article about oil separators in a Mike Busch newsletter I regularly receive. Seems he doesn't like them.

The breather air is quite hot. The three main constituents are combustion gas, oil droplets, and water vapor. The combustion gas and water vapor can be thought of as hot damp air, while the oil remains in a liquid state as small, suspended droplets.

If water is being sent back to the crankcase sump, the separator system is acting as a condenser, lowering air temperature enough to condense the water vapor to the liquid state. Only then can it return to the sump with the oil droplets, which were separated from the air by mechanical means.

If breather air is kept warm, the water vapor goes straight out the exit to the exhaust reed valve, or directly overboard in the case of no attempt at case evacuation.

Want to know if your Anti-Splat separator installation is condensing any significant quantity of water? Disconnect the drainback hose at the engine oil return port. Plug the engine return port. Stick the hose into an old oil bottle and tie the bottle to the engine mount. Go fly 10 hours and then check the bottle. Report back here.

That would be data. One measurement is worth 100 opinions.

I was talking with Bill the other day about separators. To really know the truth, we need a subject engine that has been on oil analysis for a while, say 200 hours, before having had a separator added to its breather. Run another 200 hours of with the separator, compare the printouts, know the facts.
 
Mike Busch knows more about engines than I'll ever know. I can admit that. But, in the end he is a human with opinions and preconceptions like the rest of us. With this one, at present, I disagree. We shall see in a couple thousand hours if I change my opinion.
 
...
Want to know if your Anti-Splat separator installation is condensing any significant quantity of water? Disconnect the drainback hose at the engine oil return port. Plug the engine return port. Stick the hose into an old oil bottle and tie the bottle to the engine mount. Go fly 10 hours and then check the bottle. Report back here.

That would be data. One measurement is worth 100 opinions.

....

Exactly whag I'm working on.

I'll let everyone know when the article runs.
 
Exactly whag I'm working on.

I'll let everyone know when the article runs.

Bill, As you are gathering evidence. Crankcase vacuum, say over about 5" of water, has the potential to pull unfiltered air into the engine. That might be evidenced by increased silicon in the oil sample analysis. Be careful, though, as a poor air filter or holes bypassing the filter will also have increased silicon as the air allows this to stick to the cylinder walls then get washed down. It does not take much in PPM to be a problem. That is probably the only durability issue with crankcase vacuum. Aircraft operate in a different environment that industrial engines and although the same principles apply, quantification of those principles and results differ. It may not be an issue for our birds. Just something to note as you are pursuing information for your article. BTW, I just subscribed to Kitplanes and look forward to your article.
 
Bill, As you are gathering evidence. Crankcase vacuum, say over about 5" of water, has the potential to pull unfiltered air into the engine.

The air (and silicon dirt) would have to work its way past some engine seal, but it's a valid proposal. See, another good reason to hope somebody here can present oil analysis results eventually.

Exactly what I'm working on.

Bill, BillL's note also offers a good reminder regarding your current test....seal the catch bottle to the hose if you're running an evacuator tap with the separator. If you don't, it will pull air into the system at the neck of the catch bottle and route it to the evacuator tap on the exhaust. That flow will oppose normal drainage to the catch bottle and skew the test results.

Everyone...don't get confused about discussion of vacuum in the context of Busch's objections. We are not all running identical systems. There are many choices in use:

1. Breather to overboard drain point....the usual way.

2. Breather to separator, air outlet to overboard, liquid output to catch bottle. Reduction in belly mess.

3. Breather to separator, air outlet to overboard, liquid output to engine sump. Reduction in belly mess and overall oil consumption.

4. Breather to separator, air outlet to exhaust via a reed valve, liquid output to sealed catch bottle. Reduction in case pressure and overall belly mess.

5. Breather to separator, air outlet to exhaust via a reed valve, liquid output to engine sump. Reduction in case pressure, overall belly mess, and oil consumption.

Only (4) and (5) reduce case pressure, i.e. pull a vacuum in the case. The Busch video example was probably a (2).

BTW, systems with a case evacuator (4 & 5, reed valve to the exhaust) reduce the temperature at which water vapor would condense. If you assume a pressure reduction of 3"Hg (it varies, but that's a fair average), the boiling point reduction would be a bit more than 5F. Put another way, running a case evacuator with your separator reduces the chance of condensing water and returning to the sump.

If your separator/evacuator system is operating in a hot area of the engine compartment, you further reduce the chance of condensing water. Conversely, if your GA clunker has a big leak in the rear baffle flap seal so the separator is operating in a jet of nice cool air, yep, you have a condenser.
 
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Just a data point. My -10 has the AntiSplat with vacuum valve mounted as high as it can go and drains to the motor. First dozen hours, had oil on the belly, mostly because I was adding and then watching level to try and find its "natural" level. (About 9.75 quarts.). Now I have a clean belly.

Here is some real data. I have an extra thermocouple in the engine compartment and the fues. I put it on the separator. Runs between 120 and 130 degrees F. Engine has a tight plenum, so there is no extra air except one blast tube on the mag which is on the other side of the compartment.

FYI, hot tunnel data. Right between the air valves it runs 220 to 240 degrees. My tunnel, after adding reflective insulation outside, foam inside and baffle material between the valves and firewall is still about 100. -120. Before it went over 200 with the rear heat on, about 180 with heat off. Still want more improvement, ADSB and transponder are in the tunnel, up front.
 
If you have before-and-after oil analysis to contribute, please email me.

Here are the first two contributions.

Subject #1; no water contamination. Separator with reed valve evacuator to the exhaust, negative pressure system. A small increase in silicon (dirt) is notable, but the owner reports finding a gap leaking air after the intake filter. Next oil report should tell the tale.

21tqtg.jpg


Subject #2; no water contamination. Record is less complete, and the previous report was from a different oil analysis firm. I've inserted the previous values, which were recorded prior to the installation of a separator. No evacuator reed valve on this one, so the crankcase and separator system was operating at positive pressure.

24oyrmd.jpg
 
A good discussion here. I thought I would point out a few things I learned working in an auto shop and from research. Condensation is a reality with or without separators. It is all about the cycle of condensation and burning it off.

The crankcase is always filled with combustion by-products, including H2O. When you shut down your engine, it cools from ~200* to ambient. In the process, the water vapor condenses to liquid and gravity takes it to the oil. If the next run spends a certain amount of time above the critical temps for burning off the moisture (I believe it is speculated to be 160-170 degrees), the moisture is purged from the oil. Granted, the separator will increase the load of water added back, but I bet it is minimal. Think about how little oil is returned to the case. People here are reporting one quart of oil over 25-50 hours.

I remember pulling valve covers off cars that were driven by housewives that only ran short errands. You would routinely find large clumps of white goo, that was a gell of oil and water. Those engines simply weren't run long enough at operating temp to burn off the moisture that collected each time a hot-cold cycle took place. These were cars from the 70's and 80's and they did not have air oil separators.

Condensation is a reality we all should think about and understand to ensure that our running patterns will purge it from our oil. However, with the proper cycles, you have nothing to worry about. Most all of the BMW's and many German cars use air oil separators and all return the oil to the case. When routinely taken to operating temps, these engines can easily surpass 200,000K without corrosion or other damaging issues attributed to moisture in the oil.

Larry
 
A point of contention... If you install a crankcase evacuation system on the engine ( one way valve on the exhaust connected to the breather hose ), what would be the purpose of the separator? All the moister and blowby goes into the exhaust and burns off so there's nothing on the belly anyway.. Maybe a few drops of oil would get returned to the engine but other byproducts you might not want also returns.
Race engine builders have been using crankcase evacuation systems for as long as I can remember. I've used them on cars, boats and motorcycles and they work. They are cheap and easy to install. Mr. Gasket and Moroso sell a pair for less then $50 with all the parts for two planes. I use one on my IO-360.
The added advantage is negative crankcase pressure that stops oil weeps and also the theory it increases HP by removing pressure on the piston down strokes.
 
What are the failure modes of a crankcase evacuator reed valve?

If the reed fails, it seems like there is a chance that your crankcase could be directly connected to the elevated pressure inside the exhaust manifold.

Always wondered about that.

David
 
If the reed fails, it seems like there is a chance that your crankcase could be directly connected to the elevated pressure inside the exhaust manifold.

You mean the significant and substantial rapidly alternating pressure in an individual headpipe on a 4-into-1 system (below), or the lesser, but still alternating pressures in a 2-into-1 tailpipe, or the (supposed) relatively even and moderate negative pressure at the center of a collector?

Point is that the location of the tap and the type of system is another variable.

21o7i1t.jpg
 
What are the failure modes of a crankcase evacuator reed valve?

If the reed fails, it seems like there is a chance that your crankcase could be directly connected to the elevated pressure inside the exhaust manifold.

Always wondered about that.

David

There is no pressure going back to the crankcase. The tube welded into the exhaust pipe is positioned at an angle as to cause a vacuum from the passing exhaust. Even if you have no one way valve it still pulls the blowby out. The one way valve creates the negative pressure in the crankcase from the piston pulses. I've never seen one fail.
 
There is no pressure going back to the crankcase. The tube welded into the exhaust pipe is positioned at an angle as to cause a vacuum from the passing exhaust. Even if you have no one way valve it still pulls the blowby out. The one way valve creates the negative pressure in the crankcase from the piston pulses. I've never seen one fail.

Whether or not you have seen it, they are mechanical devices and they do in fact fail. My A&P had one stick closed in this exact application and blow the front crankcase seal out. It can happen, which is why AntiSplat recommends an inspection/cleaning.

Against my guru's emphatic objection, I installed one anyway....but I'm keeping a close eye on it.
 
A point of contention... If you install a crankcase evacuation system on the engine ( one way valve on the exhaust connected to the breather hose ), what would be the purpose of the separator? All the moister and blowby goes into the exhaust and burns off so there's nothing on the belly anyway.. Maybe a few drops of oil would get returned to the engine but other byproducts you might not want also returns.
Race engine builders have been using crankcase evacuation systems for as long as I can remember. I've used them on cars, boats and motorcycles and they work. They are cheap and easy to install. Mr. Gasket and Moroso sell a pair for less then $50 with all the parts for two planes. I use one on my IO-360.
The added advantage is negative crankcase pressure that stops oil weeps and also the theory it increases HP by removing pressure on the piston down strokes.

... The purpose of the separator for our application on a typical Lycoming engine for instance, in not exactly what is commonly perceived. This devise is not intended to, and doe's not capture blow-by fumes, gassed off moisture etc and return them to the oil. These byproducts of combustion are still passed overboard and are eliminated just as before, actually more efficiently if a vacuum evacuation system is in place. On our airplanes, the separators serve to eliminate the problems associated with a very poorly designed, 1930's style inadequate breather system. The main problem being, these engines literally throw out pure clean oil that is carried up to the top of the accessory case via the cam, mag, oil pump, vacuum pump and idler gears. This is perfect oil that is mainly lost because of poor or rather no baffling. This is why the oil consumption problem becomes worse when you put in the true recommended amount of oil for your engine, rather than running it a quart or so low. The lower gears in the accessory case are running in the oil and simply carry it to the top where it is thrown out of the engine. This amounts to nothing more than a leak of pure oil if not properly addressed. This is not blow-by, nor is the engine consuming or burning oil, it is in reality simply leaking it out. The separator remedies this issue and there in no down side of any kind to its use. Thank, Allan..:D
 
There have been a few reports of failed check valves and blocked evacuator exhaust pipe ports. I previously suggested a second reed valve arranged to open if breather system pressure became positive. I've now installed that experiment, and will report back in due course. In the meantime, here's a photo of the installation in case anyone wishes to do the same:

33cra0o.jpg


I've added a red stripe to the breather outlet lines in the photo, just to make them obvious. The reed valve is the familiar NAPA 2-29000; it's just hanging from the end of the hose. The T-fitting was welded up using some 4130 tube from the scrap bin.

BTW, the blue firesleeve nicely insulates the line between the accessory case and separator, raising the separator outlet temperature to about 175F. For more in that area, kindly see the October issue of Kitplanes.
 
What's the failure mode, do they get carboned up? I have two on my Rocket, one on each exhaust pipe. I assume its pretty unlikely for both to fail at the same time if inspected regularly.

I also relocated the breather ports and incorporated them into mag hole covers, since I don't have magnetos. No separators, just straight into the PCV valves from the breathers.
 
170 hours on my separator

Just to add my experience:

After hearing the usual extremes on what to do with this, I chose to determine the best solution for myself, and run a straight tube (no check valve) into the separator found on ACS: #10570, dump the "air output" tube overboard, and collect the "oil output" in a matco remote brake fluid cylinder. I don't have any numbers from analysis, but I've been running a separator on my IO-320 for just over 170 hours and the biggest thing I've learned from my current setup is I would NEVER want the stuff I pull out of the collector to run back into my engine case.

I fly in So. Cal. for the most part, and when flying in normal So. Cal. WX (clear and dry) I get about 0.25oz of goobery-looking oil schmutz per 10 flight hours. However, when flying in humid conditions, or light mist, the 2oz. capacity reservoir will quickly fill with the usual tiny bit of dino-goober along with 2+ oz. of water.

Now that I've had enough of emptying these goobers, the next step is to plumb the "oil output" into my exhaust rather than collect it, but never back into the engine!
 
Just to add my experience:

After hearing the usual extremes on what to do with this, I chose to determine the best solution for myself, and run a straight tube (no check valve) into the separator found on ACS: #10570, dump the "air output" tube overboard, and collect the "oil output" in a matco remote brake fluid cylinder. I don't have any numbers from analysis, but I've been running a separator on my IO-320 for just over 170 hours and the biggest thing I've learned from my current setup is I would NEVER want the stuff I pull out of the collector to run back into my engine case.

I fly in So. Cal. for the most part, and when flying in normal So. Cal. WX (clear and dry) I get about 0.25oz of goobery-looking oil schmutz per 10 flight hours. However, when flying in humid conditions, or light mist, the 2oz. capacity reservoir will quickly fill with the usual tiny bit of dino-goober along with 2+ oz. of water.

Now that I've had enough of emptying these goobers, the next step is to plumb the "oil output" into my exhaust rather than collect it, but never back into the engine!

Over 2,800 hours operating time based out of SoCAL dumping oil separator condensate back into the engine. Pulled cylinders at 2,200 hours and found NO wear on the cam. Engine came off a Piper that had an oil separator that dumped back into the engine using the same port that I am using. Total Time on engine since new is over 5,700.
 
I fly in So. Cal. for the most part, and when flying in normal So. Cal. WX (clear and dry) I get about 0.25oz of goobery-looking oil schmutz per 10 flight hours. However, when flying in humid conditions, or light mist, the 2oz. capacity reservoir will quickly fill with the usual tiny bit of dino-goober along with 2+ oz. of water.

Excellent. Can I talk you into a real easy experiment before you re-plumb?

Insulate the hose between the accessory case and the separator. Separator can too, if you're game. Then fly in wet conditions and see if you still get water in the catch bottle.
 
I've had the opposite experience to Jgillis240;
My O-290 (T-18) vent tube is very short. It ends near the oil cooler in the bottom of a small plastic baby bottle with holes around the top to let vapors escape, yet collect 'most' of the oil. That oil is always very clean. I never put it back in the engine, on principle, because dust could enter the bottle thru the holes around the top, but I'm getting clean oil in the bottle, even after flights on cold days.
I'm agreeing with what I think is Dan's point, that the vapor should be hot all the way through the separator process so no condensation occurs in there. Short or insulated lines would be good.
All the water vapor and combustion gas / carbon /acids will pass through if kept warm enough.
Allan has a good point as well, (also made buy TitanXpert) the gear case on the back of the engine can pull oil up thru the meshing of the timing gears and deposit some of it in the oil separator cavity, which has a somewhat effective sheet metal separator.
A final point to keep this in perspective: All that vapor being extracted is already fully saturating the oil inside the engine. It's blowing around the rings and the piston skirts directly into the fog of oil flinging off the crankshaft. Putting back oil that has had the water & blow by gas removed is not returning oil to the engine that is dirtier than the oil inside the engine. It's simply finishing the job the internal Lycoming separator can't do.
Why don't I have one on my plane?
I'm a weight fanatic.
 
Allan has a good point as well, (also made buy TitanXpert) the gear case on the back of the engine can pull oil up thru the meshing of the timing gears and deposit some of it in the oil separator cavity, which has a somewhat effective sheet metal separator.
A final point to keep this in perspective: All that vapor being extracted is already fully saturating the oil inside the engine. It's blowing around the rings and the piston skirts directly into the fog of oil flinging off the crankshaft. Putting back oil that has had the water & blow by gas removed is not returning oil to the engine that is dirtier than the oil inside the engine. It's simply finishing the job the internal Lycoming separator can't do.
Why don't I have one on my plane?
I'm a weight fanatic.

....Good day guys
....Keep in mind that this little separator only weighs about 6 oz and it will save at the very least its weight in oil hourly. This, times a 50 hour oil change, times all the RVs and voila, we have reduced our middle east oil dependance dramatically, thus saving the world!!! Think Green!!!! Do your part now and order yours today while supplies last...:rolleyes: Isn't this forum great?...:D
 
I'm agreeing with what I think is Dan's point, that the vapor should be hot all the way through the separator process so no condensation occurs in there. Short or insulated lines would be good.

Exactly.

Breather gas water content has two sources. Water is a major product of combustion; we take a hydrocarbon, combine it with oxygen, and produce CO2 and H2O. How much H2O depends on available oxygen and how many hydrogens are available in the fuel, but won't vary a lot. The second source is atmospheric water entering with the intake air. Obviously that can vary.

Dew point rises and falls with water content; lots of water = high dew point, not much water = low dew point.

Justin describes finding liquid water in his catch can only when operating in conditions of significant atmospheric water. I'm suggesting that his breather gas is cooling enough to reach the dew point when breather water content is high, but not enough to reach the reduced dew point when water content is limited to combustion product only. Insulate the breather hose and separator, reduce heat loss, and perhaps the gas temperature will stay above the "wet" dew point.

BTW, in the context of separators, high oil temperature is good.
 
Oil seperator

My experience is different. Most of the engines I (I'm an IA/AP) have seen torn down have been from aerobatic aircraft that all had an oil separator that put the breather oil return back into the crankcase.

I can say from extensive experience that I have never observed any visible damage to the engine because of the use of the oil separator in the breather line and it's return of oil back to the crankcase!
 
Just a thought here, but I wonder....................

How much would the other 14 locations leak if the crankcase was under vacuum as happens with the vent line attached to the exhaust ???

The exhaust is not a vacuum. The intake would be, but not the exhaust.
 
Over 2,800 hours operating time based out of SoCAL dumping oil separator condensate back into the engine. Pulled cylinders at 2,200 hours and found NO wear on the cam. Engine came off a Piper that had an oil separator that dumped back into the engine using the same port that I am using. Total Time on engine since new is over 5,700.

I'm with Sobek on this subject. A properly plumbed and sited separator is a good feature, but even better is a drainable separator. It tells me a great deal about the blow-by characteristics of my engine every time I drain it at oil change.
 
The exhaust is not a vacuum. The intake would be, but not the exhaust.

Actually, both intake and exhaust have periods of positive and negative pressure.

An exhaust tap with a one way reed valve exposes the separator to repeating periods of negative pressure, much like a diode being used to rectify alternating current.
 
A point of contention... If you install a crankcase evacuation system on the engine ( one way valve on the exhaust connected to the breather hose ), what would be the purpose of the separator? All the moister and blowby goes into the exhaust and burns off so there's nothing on the belly anyway.. Maybe a few drops of oil would get returned to the engine but other byproducts you might not want also returns.
Race engine builders have been using crankcase evacuation systems for as long as I can remember. I've used them on cars, boats and motorcycles and they work. They are cheap and easy to install. Mr. Gasket and Moroso sell a pair for less then $50 with all the parts for two planes. I use one on my IO-360.
The added advantage is negative crankcase pressure that stops oil weeps and also the theory it increases HP by removing pressure on the piston down strokes.

As a former machinist and race car engine builder, I can add some to this. Vacuum in the crank case does produce horsepower, but it is really when you combine low tension piston rings that you see the most gains. Low tension piston rings reduce internal friction, but don’t seal without the differential pressure above and below the ring package. Some really low tension rings, we used 18 inches of vacuum, but then we saw increased wrist pin bushing wear. A fix for that was oil squirters into the bottom of the piston.
 
OIL SEPARATORS?

.... Oil control and blow-by issues are not an aircraft only domain. The main
difference between antique aircraft engines, and everything else is the lack of
desire to make any improvements or modernize, unless absolutely necessary.
The aircraft manufacturers for many years didn't really care if the engines dumped
oil out on the ground at every stop, or left a trail as they flew over. All other
(than aircraft) engine manufacturers, in every industry wide application,
addressed this issue some fifty years ago. All modern engines basically have an
oil separator built internally into the engine, and none of them have a pipe or
hose that spews oil out on the ground. Everything is contained inside the engine,
and these engines run two hundred thousand, or more miles with virtually no
major maintenance or repairs. I am certain everyone reading this is driving an
automobile so equipped. All certified aircraft manufactured for decades are
equipped with an oil separator from the factory, and those all return the oil to
the crankcase where it belongs. I am confident that were this the wrong approach,
the thousands of real engineers involved, with deep pockets, and unperilled
facilities to address this would be doing it differently. My thoughts on oil separators.
Thanks, Allan..:D
 
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