M-20 OIL SEPARATORS
HERE IS SOME BACKGROUND

1. Wet Vacuum Pumps:

All airplanes with gyro instruments have vacuum pumps driving the gyros. The early design of vacuum pump is lubricated and cooled by a flow of engine oil, thus called wet pumps. The vacuum produced on the suction side of the pump expels air on the output side, along with the oil. The oil returns to the engine, but the air, if returned with the oil could cause foaming, so it is expelled through a separator.

2. Wet Pump Separators:

Various designs of air/oil separators for wet pumps have been used throughout the history of flying, but none have ever worked very well. Small separators allow the air to escape through a pecan sized open vent fitting, others use a large canister to hold the oil as the air escapes. Both allow the escaping air to “spit” oil all over the engine compartment. This oily mess drove the industry to switch to “dry” vacuum pumps, although some owners have stayed with the wet design.

3. Dry Vacuum Pumps:

These do not use oil. The pump vanes are graphite, which is self-lubricating. It, also, wears quickly and is highly subject to instant failure without warning. They do run free of oil discharge, instead blow carbon dust throughout the engine compartment. Useful life is said to be from 1 to 700 hours. Their unreliability and repeated replacement are major safety and cost concerns of pilots.

Wet pumps are extremely reliable, still running after 35 years, so they have devotees who will not give them up. Our new Model 600 WP separator for wet pumps works very well, partially because it confines the spitting to its internals . See 5, below.

4. Crankcase Breather Air/Oil Separators:

Our Model 300 and 400 series of separators for crankcase breathers use a different principle. Breather air is ladened with both oil mist and water vapor. The oil mist is from pumping and splashing the oil in the crankcase. The water vapor comes from boiling off the humidity and the combustion by-products, which under normal pressure, blow by the piston rings and valve guides into the crankcase. Our separators for the crankcase breathers collect and liquefy the oil mist, returning it, drop-by-drop, to the engine. The water vapor remains in suspension and exits with the air.

5. Wet Vacuum Pump Oil Separators – How They Work

Our wet pump separator takes the oil and air into its primary chamber. The oil, as it is separated, falls to the bottom and drains out the oil return line. The high pressure air vents overboard leaving the oil chamber pressure free. All the oil spitting is self-contained.

The principles and the air pressures for the two types are so different that the functions cannot be combined successfully.  The old-fashioned attempts to combine them have failed.

I hope this helps for the basic understanding of air/oil separators.

~ Bill Sandman ~

Home | About Us | Search | Contact | Lifetime Vacuum Pumps
Breather Separators | Vacuum Pump Separators | Turbo Kits