dsc85222.jpg

Detail of the line (travelling downward, then to the left, and into a square block with four bolt heads) carrying high-pressure fuel from the main fuel valve outlet to the the hypergol manifold.

During engine bootstrap, when the fuel pressure from this high-pressure duct is high enough, it ruptures the hypergol igniter diaphragms and forces pyrophoric fluid (fluid which spontaneously combusts upon contact with oxygen) into the thrust chamber through igniter fuel orifices in the injector.