The Mistsubishi turbos found on most turbo powered Volvos are oil and water cooled. They therefore have an oil feed and drain metal pipe and a water (coolant/anitfreeze) feed and drain going into the Central housing.
As well as an air feed coming from the air filter and a boosted air out on the compressor housing (coldside) and exhaust gases going into (from the exhaust manifold) and out of the turbine housing (hotside):-
Ignore the white exhaust paste I put on the downpipe to check for exhaust gas leakage!