Pretty close Gaboon
The seals are indeed a piston ring type seal. They are compressed when installed to leave minimal gap between the ends of the rings and around the rings. This is a torturous oil path to prevent leakage into the air/exhaust passages. Most turbos use only a single piston ring on the compressor/turbine sides to reduce drag on the rotational assembly to max out mechanical efficiency. It's not uncommon for 2 rings to be used on both the compressor and turbine sides in applications where oil leakage would cause problems (i.e. emissions).
On the compressor side, there is usually an oil splitter which throws oil away from the seal as it is spinning. The piston rings and the splitter are dynamic seals...the faster the turbo spins, the better the seal works.
Here's an explanation from Forced Performance:
Forced Performance said:
The seals within the turbo are not meant to hold back a bearing housing that has become full of oil. They are designed to sling the oil mist and spray within the bearing housing away from the point where the shaft comes out each end. If the bearing housing becomes full of oil it will ooze out past even brand new seal rings.
The oil should freely drain out of the bearing housing as quickly as the engine supplies it. This is why the drain tube is so much larger than the supply tube. Gravity is the only force moving the oil out of the turbocharger. Any slight restriction in the oil drain tube, even a small silicone dingle berry, can slightly impede the draining of the oil and cause oil to back up into the bearing housing.
The crankcase vents are the second largest cause of oil loss from a good condition turbocharger. The seals in the turbocharger were designed with expectation that the pressure inside the compressor and turbine housing will always be greater than the pressure in the bearing housing. If this is ever not the case then oil will come out pass the seals. A restricted crankcase vent will cause this to happen. If the amount of ring blowby exceeds the ability of the crank vents to release the pressure positive pressure will build within the crankcase. This pressure within the crankcase can exceed the pressure inside the compressor and turbine housings under some operating conditions resulting in oil being driven pass the seals by the improperly biased pressure gradient across the seal rings. In severe cases it may be necessary to introduce vacuum pumps to deal with crankcase pressure, but these would be very severe high boost applications where even low percentages of blowby produce a high volume of crankcase vent flow.
I posted that to illustrate a point. The seals depend on differential air/exhaust pressure to keep the oil in the center housing...i.e. pressure is exerted inward on the center housing. For those that have done Cletus mods to the PCV system and think vac is not necessary for the PCV to work correctly need to think out that idea again
The short answer: A turbo sitting on the shelf full of oil will very likely leak.
