The Walker AirSep uses a large enough air volume (hence its larger size) and a tiny amount of vacuum pump discharge air, to help condense the oil inside the AirSep, and to overcome crankcase pressure to return collected oil to the engine while the engine is running. Competitive systems are only gravity flow so no oil returns into the engine until the engine is completely shut off. Walker AirSeps are complete with everything you need to install it onto the airplane. One system is large enough to clean both the engine breather oil and wet vacuum pumps discharge.
For over 25 yrs, Walker Engineering made THE best Air/Oil Separator money could buy. Unfortunately, in 1997, Walker was so busy supplying the OEM diesel & marine engine mfgs with AirSeps, they just didn't have time to build them for aviation and ceased production. Airwolf acquired all the rights and STCs from Walker Engineering and has expanded the eligibility listing to include all piston powered aircraft. If it burns avgas, then Airwolf has an air oil separator approved.