The Proof:
The crankcase air/oil separator task, as the name implies, is to separate the air from the oil in
the breather line. The air is vented overboard and the oil is returned to the crankcase. Perfect
proof is when the oil is at the FULL mark, the top two quarts no longer blow away, the breather vent stays clean and the
crankcase pressure is unaffected. Only M-20's separators have been FAA approved
under these parameters. Others show quick failure when the oil is topped off.
For wet vacuum pump air/oil separators, the air pressure from the pump, which is as much as
43 times greater than crankcase pressure, must be vented completely, but without spitting out the pressure propelled oil. The oil must be separated
and reduced to crankcase pressure. Perfect
proof is when the measured crankcase pressure is unaffected by the separator and the air exit
remains clean. Only M-20's separators have been proven to meet these requirements. Others admit to using vacuum
pressure to push the oil back to the crankcase. That pressure can make a new engine run like it
was old and at TBO.
The Scientific Basis:
Crankcase Breathers
All internal combustion engines breathe. As they cool
after shut down, they inhale air. Humidity in the air condenses into liquid water overnight. Much
more water is generated as a bi-product of combustion while the engine is
running. At operating temperatures this water boils changing from a liquid to the gaseous form, water vapor. The vapor
combines with the air in the space above the pool of oil in the crankcase
sump. From there it vents out the breather line.
The air, also, holds oil particles. These are formed by a variety of
activities. Rapid action of the crankshaft, piston arms and connecting rods violently splashes the
pool of oil in the sump. Adding to this turbulence is the force of the oil pump
which sucks oil from the bottom of the pool and pushes it through passageways in
the upper engine housing, sprays it on moving parts, lubricating, cooling
and cleaning the entire innards of the engine. In all this mayhem, some of the
oil is aerated as tiny droplets of mist.
Of the three elements, air, water and oil, the water is the best solvent, so it
picks up the corrosive acids that are present in the blow-by. The air, a gas,
flows up and out of the crankcase through the breather line, carrying the water
vapor, which is also a gas, and the oil mist, which is a liquid in particles so
tiny that they, too, are air borne. A well-functioning separator, placed at the
highest point in the breather system, vents both the gases with their
contaminants but diverts the liquid oil for continuous return to the crankcase.
It is important that the return not be delayed and the water vapor not be
condensed, both of which happen with the old era larger sized
separators. Oil in prolonged contact with water makes
sludge. The large, old-style, inefficient separators retain
oil and water. That makes sludge, so they
include a filter in a futile attempt to keep the oil off the belly. Making
separation particularly difficult is the extremely low crankcase pressures at which piston engines
operate. The pressures have a narrow range of from 1" of H2O for a new engine, to 3" H2O for a
run-out, engine. At 4" the blow-by is too great for the pilot to complete a satisfactory run-up.
Getting the oil to return to the engine at these critical but low pressures rules out the use of any added pressure,
such as connecting the vacuum pump to force the oil return. (Some separators attempt this with
unknown damage to the engines.) Gravity, at ambient pressure, is the only safe, practical choice. To
keep the water vapor from condensing, the separator must be very small.
This prevents the water
vapor from rapidly expanding, cooling and condensing. Additionally, the oil should not be allowed to
pool up as it can in a large separator where the water condensing after shut down will combine with it
to form sludge.
Wet Vacuum
Pump Separators Engine oil lubricated vacuum pumps are called "Wet Pumps" as opposed to "Dry" pumps which
are self-lubricated. Dry pumps lubricate by wearing away the carbon vanes.
Dry pumps burn out without warning,
much like a light bulb. In a split second the vanes disintegrate to dust. The gyros they drive
continue running for a while as they slow down and then roll over. Because this
gradual change can escape the pilot's scan, it too frequently leads to fatalities.
Wet pumps, on the other hand, are
not known to fail. They run for decades, showing the need for overhaul months before
their operation becomes marginal. Wet vacuum pumps became unpopular years ago only because they spit oil over everything.
The M-20 goal is to bring back the wet pumps to popularity by making them run
clean. The oil that wet pumps spew out with their exhaust air, (at rates of 3.38 ounces per hour for those
powering instruments, to 6.42 ounces per hour for those also inflating boots) is
a liquid stream, propelled at
generally 3.4" Hg (1.7 PSI). This is not much oil when compared with crankcase breathers,
but it is a liquid, not an oil mist. It is significant that this outlet pressure is 43 times greater than that of a good engine
crankcase and about 15 times greater even than a run-out engine.
Inappropriate separator design, which allows added pressure into the crankcase, can
rob your engine of its operational newness or deteriorate its already partially worn condition.
The difficulty, unique to vacuum pump separators, is that to safely return the
liquid oil stream to the crankcase, the vacuum pump pressure must be vented without
losing the oil. This is a challenge which requires an entirely different separation technique from that of the crankcase
aerated oil mist. History has shown that attempts to combine both functions end in poor results.
Design
The M-20 designs were created from this knowledge which seems to have escaped all the prior
manufacturers. No other separator has the design features to overcome each of these
different problems. No
other separator has the level of performance to prove these values.
Aviation Air/Oil Separators of many designs have been around since the early days of the round
engines. History indicates that none of
them has worked well. The proliferation of
separators today, ranging in price from $35 to $1200, seems to have been spawned
by the popularity which M-20's success has given to
separators. Price, alone, does not indicate the quality of performance. A pilot phoned from Canada to report that he had been furious
that a $1,200 crankcase separator was added to his purchase of a
factory new heavy single on floats. Upon delivery to his lakefront home, the floats and the fuselage
were coated with oil. The factory accepted return of the separator with a
$1,200 credit. The pilot reported back to us that our Model 300 replacement was doing a
perfect job at less than 1/4 the cost.
Separators have been used in automobiles, too. Ford Motor Company's' engineer for "Special
Cars" bought one of ours for his airplane. He related that when Thunderbirds were being raced,
they were banned from many tracks because their breathers blew out so much oil that
they created a
safety hazard for cars following them. "What do you stuff yours with?", the Ford engineer asked.
"We tried everything and nothing worked". We at M-20 don't stuff ours with anything. We have
designed a 5-stage system for separating the oil without disturbing the water vapor so it
can be blown
away with the air. Others have faked a "centrifugal" design, ignoring the fact
that pressures coming
off the crankcase could not blow out a birthday candle, much less set up a spiral flow
powerful enough to sling
out the oil. Other separators are large cans which cause a pressure drop sufficient to condense
the water vapor into liquid and hold it in the large canister, inviting sludge
formation. In at least one design, in what appears to be an admission of
non-performance, the separator discharge is piped into the engine
exhaust where the 1600 degree temperature guarantees to incinerate the oil that has passed
through the separator. Stuffing separators with any filter material just retains
a portion the oil. The rest blows out with the air to grease the belly.
Blowing
water over the oil covering the filter, makes sludge, so periodic cleaning is necessary.
M-20 crankcase models use a 5-stage, ambient pressure process, which includes two oil collection
stages, a tiny sump with a capacity of only a few drops of oil controlled by a weir, an air scrubber
and a anti-siphon device. Our wet pump model uses 4 very different stages,
2 oil collection
stages, a pressure relief device (small size precludes water vapor condensation) and an anti-siphon device. Gravity is the only force needed to return the oil.
M-20's crankcase and the wet pump separators will always be two independent units. Putting two
air pressures together, one 43 times greater than the other, yet keeping the oil
to crankcase
pressure, while doing two very different separation processes in the same vessel, makes no sense
to us. Two small vessels makes good sense and good science.
What to Watch for in Selecting an Air/Oil Separator
1. Avoid large Separators that are much greater in diameter than the line that feeds them.
They will tend to condense the water. Our separators for engines from 45 hp to 315 hp are 2" in
diameter. Those that go to 950 hp are only 2 1/4" in diameter.
2. Avoid Separators which add vacuum pump pressure to
force the oil back to the crankcase. These may be responsible for blown out crank seals. Vacuum pump pressure is 43 times
greater than a good engine crankcase pressure and 15 times greater than a run-out engine can
tolerate. Ours need no force other than gravity.
3. Avoid coalescing filters masquerading as air/oil separators. Tip-off: they have cleanable
elements. The elements "coalesce" (gather together) some of the oil mist particles in a filter
medium (generally metallic wool). Once coated, the rest of the oil blows through
the filter and the oil left behind becomes sludge. Filters require periodic cleaning.
4. Avoid using a separator that mounts to the baffle, especially a large
separator.
Cracked baffles can result and the replacement cost is high . Ask any Bonanza or Baron owner who has experienced this.
Summary: Why Only M-20 Air/Oil Separators Really Work
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1. Will not condense the water vapor into liquid water.
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a. The gaseous vapor exits with the air
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2. Returns the oil in its cleanest condition without exposing it to water.
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a. The oil remains clean longer. Sludge is not formed
in the separator, so clean-out is unnecessary
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3. Requires no addition of pressure to force the oil back to the sump
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4. Anti-siphon venting system will not support any pressure build-up in the crankcase.
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5. M-20 Separators' STCs cover all certified makes and models of airplanes and
helicopters, currently covering a range of from 45 hp to 950 hp. They are
the best for Experimentals, too.
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| 6. Flight proven on thousands of aircraft, probably more than all others combined.
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7. These are the only separators that will allow your engine to fly with the oil at the
full level and not blow any out, even the top 2 quarts!
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8. Oil lubricated Vacuum Pumps Run "Clean" with Model
600WP.
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