These are relief valves, with nozzles attached, that go with the Viking Orbiter Propulsion System. The system had three important functions. These were to: make course corrections during the trip to Mars, slow the spacecraft for Mars orbit insertion, and make Orbiter steering maneuvers during Mars orbit. The system consisted of a single 300 pound thrust, multistart rocket engine, mounted on a moveable gimbal. It used two side-by-side propellant tanks containing the fuel and oxidizer and a smaller, spherical tank for the helium used to force in the propellants into the combustion chamber. The propulsion system, with relief valves, was transferred to the Smithsonian in 1996 from the NASA Jet Propulsion Laboratory. It is not known if these relief valves and propulsion system were backups.
Transferred from NASA - Jet Propulsion Laboratory