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Views of the turbopump and heat exchanger.

Picture 3 of 4.

After spinning the turbine to drive the turbopump, the hot gas from the gas generator (on the opposite side of the engine) is run through the heat exchanger. The four lines leading into and then back out of the heat exchanger are the oxygen and helium lines used to pressurize the S-IC stage's LOX and fuel tanks, respectively.

After running through the heat exchanger, the turbine exhaust flows through the bellows and into the turbine exhaust manifold (around the exit plane of the engine). It is then routed to the nozzle extension. This gas, much cooler than the main engine's exhaust gas, is vented through gaps in the shingles comprising the nozzle extension's inner wall, and provides film cooling to the otherwise-uncooled nozzle extension.