In article ,
says...

On 2019-07-20 10:16, Jeff Findley wrote:

Scott Manley's video showed springs pushing valve down (to illustrate
the backflow prevention). Is this how the real valve would function?

Yes.

systems than I do) speculate is that (relatively warm) gaseous NTO snuck
past the check valve and then re-condensed to liquid in the (relatively
cold) helium plumbing.


Shoudln't a check valve prevent passange in wrong direction on either
gas or liquid? It's not like there is a floater that rises up to close
valve is liquid rises up, is it?

You really can't rely on a check valve for this. That's why designs
also include (usually redundant) isolation valves. No, I don't know why
NASA "has always done it this way" if an isolation valve would have been
better.

Also, would the titanium tubing between the compreseed He2 and NTO tank
be at same temperature as NTO tank until the He2 valve is opened? Why
would it be colder?

Higher pressure during an event like loading the tank with NTO could
result in higher temperatures of the NTO in the tank (unless the NTO was
cooled prior to loading to prevent such a thing from happening). Higher
pressure could have been used to drain the tank as well, so we just
don't know, because SpaceX has not provided details which would have
caused such a condition.

Again, SpaceX just said that the issue was caused during "ground
processing". The only two events which might have caused this would
have been loading or draining the tank. Otherwise, the tank would have
been at ambient temperature, just like the rest of the plumbing.

If Helium is kept liquid at very high pressure,
won't it also be at room tempoerature? While being filled, I can
understand initially getting cold as liquid helium is dumped into empty
tank and can vaporize, but after a while, doesn't it get warm as they
compress that gaseious Helioum back to liquid as more liquid is pumped in?

Yes, loading the helium as a liquid could have chilled the plumbing on
the helium side. That could have caused very low pressure on the helium
side, especially if any air or nitrogen in the lines turned to liquid.

Jeff
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