Detail of the fuel return manifold.
Fuel flows down two adjacent tubes, cooling the engine wall (known as
"regenerative cooling"). It reaches the fuel return manifold (the silver ring
at the exit plane of the thrust chamber), where it returned through two "up"
tubes, reaching the fuel manifold and then being injected into the combustion chamber.
Note the marking for No. 120
tube. Even though this is a "fuel-down" tube, the arrow is for some
reason pointing up (i.e., toward the throat). This marking is between two
tubes; presumably, the tubes on either side of this mark lead back up to the
No. 120 tube at the bifurcation joint.