Apollo Saturn S-II (Second Stage) liquid hydrogen vent and relief valve
This Apollo Saturn S-II (Second Stage) Liquid Hydrogen (LH2) dual function tank Vent and Relief Valve was manufactured by Wallace O. Leonard Inc. under subcontract to North American Aviation (prime for the S-II). The valve was produced in 1966.
The LH2 Vent-Relief valve, used as part of the single Rocketdyne J-2 engine system which powered the stage, was situated at the top/forward portion of the S-II LH2 tank. It was commanded via the Pneumatic Control System (helium gas driven). The Vent-Relief valve opened during ground fill/drain of the propellants and closed prior to pressurization. Additionally, the valve enabled venting while in flight if either of the tanks experienced overpressurization. The Vent-Relief valve output was applied to a nonpropulsive vent system (expelled gas was routed to two ducts positioned at 180 degrees on either side of the stage resulting in total thrust cancellation).
The valve is 21" tall and 12.5" in diameter at the widest point. It weighs 45 pounds.