The S-IVB also ongoing to thrust at a very low level by venting gaseous hydrogen, to maintain propellants settled of their tanks and prevent gaseous cavities from forming in propellant feed traces. This venting also taken care of Protected pressures as liquid hydrogen boiled off during the gas tank. https://edge-ai19630.p2blogs.com/32852854/not-known-facts-about-apollo-3-5-blue-plus-processor