On aircraft equipped with Wet Vacuum Pumps, M-20 Oil Separators states that two of their air/oil separators are better than one. “Airplanes equipped with wet vacuum pumps are usually 30- to 50-year-old aircraft and are generally well maintained,” states Bill Sandman, M-20 President. 

“Pilots of these aircraft are accustomed to a large canister-type filter/separator attached to both their engine breather and their wet vacuum pump exhaust.  There is a growing trend to replace these older combination separators with two M-20 separators because of increased performance and efficiency. 

But a common question is: Why does it take two separators to replace one combination unit?”

In clarifying the two-separator M-20 solution, Sandman said, “The engine breather sees faint pressures ranging from 1” H2O on a new engine to 3” H2O on a run-out engine.  These pressures are too small to be measured in Hg or PSI—common aviation values—they are just a tad higher than atmospheric pressure.  Vacuum pumps output 4.6” Hg.  That is about 46 times greater than crankcase pressure—an amount that would kill any engine.  Attempts to co-mingle these two pressure extremes in a single separator device requires compromise resulting in poor separation performance for both the breather and the vacuum pump.”

Sandman added, “The two separation tasks differ greatly.  The engine outputs copious amounts of air and water vapor, plus about one quart-per-hour of aerated oil, all at extremely low pressure while the wet vacuum pump blasts out a stream of liquid oil propelled by high pressure air. 

M-20’s breather separators instantly divide the oil from the air-water vapor mix.  This returns the oil to the engine as quickly as the mist can be formed into drops.  At the same time, the gas mix is vented immediately.  It is a quick, non-pressure process. There is no other way to get the job done proficiently.  For the wet vacuum pump, the blast of high pressure air must vent, but the liquid oil has to be tricked into a diverging path to the return line so as not to be aerated and sucked out with the air.  Neither of these tasks is easy—both require precision and an have intolerance to being set off balance by the other.  For these reasons, and to insure optimum performance, we promote the two-separator solution.”

FMI: www.m-20turbos.com