Azimech,
I've posted below a picture of the DB hydraulic coupling.
This is probably the most spectacular one available because of the colour! If you look carefully, you will see the part of the duplex coupling driven by the engine is the two OUTER sides (colored red) of the Fottinger couplings, while the inner pair(pink) is connected to the impeller.
This is the opposite to the early DB couplings and it was introduced because it was easier to cool the outer parts. If you look at the end of the arrow on the "Kuhl Ol", you can see the oil sprays in brown.