The S-IVB also continued to thrust at a small amount by venting gaseous hydrogen, to keep propellants settled inside their tanks and prevent gaseous cavities from forming in propellant feed strains. This venting also taken care of Harmless pressures as liquid hydrogen boiled off while in the fuel tank. https://hearables65307.rimmablog.com/33077734/not-known-facts-about-apollo4-plus