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This question was inspired by the answer to this question. The answer, in part, states that overpressurization of propellant tanks is a cause of upper stage explosions, leading to orbital debris.

The only propellant tanks I am familiar with, those in the STS External Tank, had relief valves that would pop open if the the tank pressure reached a certain value.

After reading about the suspected cause of the latest Falcon 9 anomaly, I assumed that the second stage relief valve was undersized for the rupture of a helium sphere - a design error. But perhaps there was no relief valve at all?

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  • $\begingroup$ I thought that the Falcon 9 anomaly was due to a struct which did not handle the force exerted by the thrust. $\endgroup$ – ChrisR Oct 6 '15 at 14:24
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    $\begingroup$ That was the initial failure. The failure chain goes: The strut failure released a helium tank, which maybe tore loose from its plumbing, but anyway vented all its helium into the prop tank, exploding it. $\endgroup$ – Organic Marble Oct 6 '15 at 20:27
  • $\begingroup$ There are 2 different systems that are both called relief valves, see my answer. The STS ET uses one system, the Ariane 4 and 5 use the other. $\endgroup$ – Hobbes Oct 7 '15 at 10:29
  • $\begingroup$ Shuttle used a combo vent/relief valve. $\endgroup$ – Organic Marble Oct 7 '15 at 11:47
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Since Centaur Upper Stage has a long flight history*, and it did experience hydrogen-venting problems in its early versions resulting in several modifications to its pressurization system, I was fairly certain that it ought to have several relief valves in place;

From CENTAUR D-1T PROPULSION AND PROPELLANT SYSTEMS, William E, Goette, Lewis Research Center, 1973 AIAA Propulsion Joint Specialist Conference proceedings (PDF):

Propellant Tank Venting and Pressurization

The Centaur liquid hydrogen and liquid oxygen propellants are contained in thin-wall, pressure-stabilized tanks. Pressures in each tank are maintained by propellant boiloff. Vent valves are used to control pressure levels during tanking and flight. All of the vent valves are of the same design, differing only in pressure setting. A solenoid in each valve may be energized to place the valve into a shutoff mode to preclude venting.

The liquid oxygen vent system is mounted on the aft bulkhead and consists of one vent valve, insulated ducting, and a vent disconnect. This system is shown in Figure 7. Venting on the launch pad occurs through the disconnect and a duct which penetrates the interstage adapter. After separation from the Titan booster, venting will occur overboard through the ducting. The ducting is aft canted, and adjustable (prior to launch) such that the thrust from the vented gas is directed through the vehicle center-of-gravity. This orientation minimizes disturbing torques while venting.

The liquid hydrogen vent system is located on the forward bulkhead as shown in Figure 8. It consists of two vent valves, a plenum, ducting, two aft canted vent nozzles, and two inflight vent disconnects. Venting on the launch pad and during ascent prior to Centaur Standard Shroud (CSS) separation occurs through one leg of the vent system and overboard through a shroud-mounted vent fin. After CSS jettison venting occurs through both legs of the system.

This system is symmetrical, which provides equal thrust forces from the two vent nozzles. The nozzles are canted aft 30°, so that a positive forward force is produced on the vehicle. In the event the propellants are not completely settled at the time of venting, or if there is some liquid entrained in the vent gas, the additional thrust will help settle the propellants and reduce any problem.

Two vent valves are used to control hydrogen tank venting. The primary vent valve controls the tank pressure during most of the prelaunch and flight operations. However, a requirement exists during boost flight for a higher tank pressure to react flight loads. The secondary valve is set to operate at a higher pressure level than the primary valve, and serves as a relief or safety valve during this period of flight. A solenoid has been added to the secondary vent valve in order to disable the valve during the long zero-gravity coast periods. This permits higher tank pressures to be attained, and reduces the number of tank vent sequences. Except during the boost phase of flight, the vent valves are controlled by a system known as the Computer-Controlled Vent and Pressurization System (CCVAPS). This system will be discussed in detail in the section termed Propellant Management.

Centaur Upper Stage Propellant Vent Valves

And so on and the same source also describes the use of solenoid valves on the RCS and Hydrogen Peroxide systems, and explains a bit more the interstage purging system.

I know, this qualifies as vintage, but even today's Centaur screams legacy throughout, so I wouldn't be surprised if none of this changed substantially at all since they resolved problems with hydrogen-venting system's fire hazard that destroyed the first Atlas-Centaur (F-1) mid-flight. But I'll keep my eyes peeled for anything newer. Also see Taming Liquid Hydrogen: The Centaur Upper Stage Rocket 1958-2002, Virginia P. Dawson and Mark D. Bowles, 2004, The NASA History Series (PDF).

*Centaur was launched 228 times, as of October 2, 2015.

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  • $\begingroup$ All these answers had good info, but this one's excellent. $\endgroup$ – Organic Marble Oct 7 '15 at 3:07
  • $\begingroup$ Good job tracking down all this info! $\endgroup$ – called2voyage Oct 7 '15 at 13:02
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The Saturn I, IB and Saturn V rockets had a relief valve system for the S-IVB upper stage. I could not find any documentation of a relief valve system for the Falcon 9 upper stage.

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Possibly not what you're looking for, but the Apollo LM's fuel tanks used helium pressurization, and the helium tanks had burst disks (or diaphragms). When pressure in the helium tanks got too high, several days into the mission, they'd pop and vent to space. This means no more pressure in the fuel tank, but this would normally happen well after the lunar landing, after the LM was abandoned. On Apollo 13, they didn't land, and kept the LM on the trip back, so in both the transcript and the film, there's some discussion of when they could expect the "bang" of the burst disk.

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    $\begingroup$ Didn't one of the early LM-equipped Apollo missions have a prelaunch issue involving the helium burst disk as well? (Separate from the Apollo 13 burst disk incident.) $\endgroup$ – a CVn Oct 7 '15 at 13:01
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There are 2 different systems that are both called relief valves:

  • One is pressure-actuated (this is also used on e.g. steam boilers) and makes sure the pressure doesn't rise above a preset value.
  • The other seems to be more common in rocket stages. While the stage is in use, this valve is inert. After the the stage is discarded, this valve opens to dump any remaining propellant.

The upper stage of the Ariane 4 had pressure relief valves. These were added after an explosion on an early Ariane 4 upper stage. These valves are used to dump all remaining fuel overboard after the stage has been expended.

The ESC-A upper stage of the Ariane 5 also has valves that are used to dump all remaining fuel overboard after the stage has been expended.

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  • $\begingroup$ Thanks, I was trying to find information on Ariane but hadn't come up with anything yet. $\endgroup$ – called2voyage Oct 6 '15 at 20:49
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    $\begingroup$ Your second example would have been called a vent valve on STS since it did not serve to protect the pressure vessel by opening at a set pressure. STS ET used a combination type of valve that could be commanded open to vent (during fill ops for example) then placed in relief mode for flight. $\endgroup$ – Organic Marble Oct 7 '15 at 11:52

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