3 ms·

I can't think of the manufacturer of the top of my head, but there are definitely off-the-shelf options. They are used on the LN2 tanks and dewars you see at a

I can't think of the manufacturer of the top of my head, but there are definitely off-the-shelf options. They are used on the LN2 tanks and dewars you see at a lot of electronics (and I'm sure other) manufacturers, and I'm pretty sure are standard kit for any cryogenic vessel. I think the bigger issue, as one commentor alluded to, is that you might not want to vent whatever is in the rocket straight to atmosphere.

dogma1138 10y ago
LN2 isn't combustible. LN2 isn't stored at the high pressures that cryogenic LOX and RP-1 are. RP-1 has a flashpoint of 110f, liquid oxygen would turn pretty much every spark into a party including turning a lot of materials which are not normally combustible under atmospheric levels of oxygen highly combustible. Basically once the cryogenic fuel starts to warm up you have to launch or to empty the tanks, the tanks are pumped out into reservoir tanks which are usually below the launch pad and fueling or emptying the rocket is in general the most dangerous part of the launch/abort sequence. Temperature and pressure variance, vibrations, leaks, and a lot of moving parts if anything goes wrong it can result in a pretty big explosion. Overall they do have ways to empty the tanks, but this is a controlled pump out of the fuel at pressures and rates that would be as safe as one can get when dealing with supercooled liquid oxygen and kerosene, uncontrolled venting is a big no no. You can similarly see this on larger tanks of both inert and reactive gases, a small propane tank could have a PRV because a flame out is likely to be less dangerous than an explosion in a BBQ setting, a tanker won't have a PRV because if it vents several tons of propane the result would be as bad or worse than a potential or an actual explosion. LN2 tanks also have PRV's as long as they are small enough to be safely vented but as soon as you go into a large enough volume where venting it is no longer safe whatever fail safe you implement has to be controllable.
- TFortunato 10y ago
  Thanks for the info! My experience in the past was mainly with large LN2 dewars, with liquid helium refrigerators added to re-condense the N2 gas back to a liquid, limiting the pressure (and limiting how often you needed and LN2 refill!). We had blow-off valves as a fail safe if pressures got too high if the cooling head ever failed. I'm sure working with cryogenic fuels is a whole different world. As I commented, it's not that there aren't cryogenic temperature pressure relief valves, just that they may not be what you want!
  - dogma1138 10y ago
    >As I commented, it's not that there aren't cryogenic temperature pressure relief valves, just that they may not be what you want! Yeah for sure, if you think about it even if the rocket was filled with inert gas venting it might be very tricky. You have an erect rocket on a launch pad, you have to vent evenly as a pressure relief valve is effectively a "rocket engine" at high enough pressures. If one of them freezes and you don't have even distribution it can topple over. You also have to vent the tanks in order and at a certain rate I would assume for example you want to vent to top tanks first to prevent the rocket from becoming too top heavy, and you also want to vent it at a certain rate to prevent quick shifts in the balance and weight distribution of the rocket.
- stcredzero 10y ago
  liquid oxygen would turn pretty much every spark into a party including turning a lot of materials which are not normally combustible under atmospheric levels of oxygen highly combustible. Nickel and steel would combust during tests of the SSMEs. (Space Shuttle Main Engines) Even increasing the fraction of gaseous oxygen in the atmosphere can turn all sorts of surprising things combustible. (Like living human flesh!)

dogma1138 10y ago

LN2 isn't combustible. LN2 isn't stored at the high pressures that cryogenic LOX and RP-1 are. RP-1 has a flashpoint of 110f, liquid oxygen would turn pretty much every spark into a party including turning a lot of materials which are not normally combustible under atmospheric levels of oxygen highly combustible. Basically once the cryogenic fuel starts to warm up you have to launch or to empty the tanks, the tanks are pumped out into reservoir tanks which are usually below the launch pad and fueling or emptying the rocket is in general the most dangerous part of the launch/abort sequence. Temperature and pressure variance, vibrations, leaks, and a lot of moving parts if anything goes wrong it can result in a pretty big explosion. Overall they do have ways to empty the tanks, but this is a controlled pump out of the fuel at pressures and rates that would be as safe as one can get when dealing with supercooled liquid oxygen and kerosene, uncontrolled venting is a big no no. You can similarly see this on larger tanks of both inert and reactive gases, a small propane tank could have a PRV because a flame out is likely to be less dangerous than an explosion in a BBQ setting, a tanker won't have a PRV because if it vents several tons of propane the result would be as bad or worse than a potential or an actual explosion. LN2 tanks also have PRV's as long as they are small enough to be safely vented but as soon as you go into a large enough volume where venting it is no longer safe whatever fail safe you implement has to be controllable.

TFortunato 10y ago
Thanks for the info! My experience in the past was mainly with large LN2 dewars, with liquid helium refrigerators added to re-condense the N2 gas back to a liquid, limiting the pressure (and limiting how often you needed and LN2 refill!). We had blow-off valves as a fail safe if pressures got too high if the cooling head ever failed. I'm sure working with cryogenic fuels is a whole different world. As I commented, it's not that there aren't cryogenic temperature pressure relief valves, just that they may not be what you want!
- dogma1138 10y ago
  >As I commented, it's not that there aren't cryogenic temperature pressure relief valves, just that they may not be what you want! Yeah for sure, if you think about it even if the rocket was filled with inert gas venting it might be very tricky. You have an erect rocket on a launch pad, you have to vent evenly as a pressure relief valve is effectively a "rocket engine" at high enough pressures. If one of them freezes and you don't have even distribution it can topple over. You also have to vent the tanks in order and at a certain rate I would assume for example you want to vent to top tanks first to prevent the rocket from becoming too top heavy, and you also want to vent it at a certain rate to prevent quick shifts in the balance and weight distribution of the rocket.
stcredzero 10y ago
liquid oxygen would turn pretty much every spark into a party including turning a lot of materials which are not normally combustible under atmospheric levels of oxygen highly combustible. Nickel and steel would combust during tests of the SSMEs. (Space Shuttle Main Engines) Even increasing the fraction of gaseous oxygen in the atmosphere can turn all sorts of surprising things combustible. (Like living human flesh!)