# Why were hypergolics tanks vented manually?

As I'm reading "Ignition!" I'm finding one point baffling: vapor pressure being such a big deal. Outgassing of both fuels and oxidizers would cause dangerous pressure build-up. The book describes the hair-raising stress of handling materials that release oxygen. The utter horror of watching technicians estimate the pressure by measuring barrel bulging. The stringent requirement for periodic manual venting. Abandoning one promising line of research purely due to unacceptable vapor pressure.

A check valve is a really simple, cheap, small device that would neatly protect the contents of the container from environment, while allowing whatever accumulates in the container to vent once the pressure inside rises above a preset value. Even equipping individual barrels with these would cost pennies. Did no-one think of that, or is there some other reason making this impossible or impractical to such a degree that vapor pressure would become an insurmountable problem?

• aka "relief valve" – Organic Marble Jan 12 '17 at 15:30
• I'm not sure I like the idea of tanks filled with hypergolics venting automatically, in a potentially unknown environment (could be an atmosphere, could be a vacuum, might even be during reentry or orbital maneuvering)... I don't know to what extent this entered into the considerations, but it would definitely be among the first considerations on my mind if I considered adding something like that to a design! – user Jan 12 '17 at 15:50
• All the manned US ships had pressure relief valves, usually on the helium for the rcs and often many other places too. – Innovine Jan 12 '17 at 17:15
• @Michael kjörling I'm not sure I like the ioea of the hypergolic tanks not venting, either, and possibly bursting in an uncontrolled manner. I guess the controlled venting can at least be directed so as to not trigger problems with other tanks, plumbing and whatnot. – Innovine Jan 12 '17 at 17:17
• @MichaelKjörling: this nearly universally applied to long-term storage - fuel for missiles. In many cases the products were fairly benign too - release of $O_2$ appeared most hated in particular, even though in case of constant venting the concentrations would be entirely harmless. – SF. Jan 12 '17 at 18:38