Your/any cryo/LOx system should have failsafe valves. If you lose
pneumatic or electrical signals your valve returns to their anomaly safe
position. Springs do this well. All ball valves have to be drilled to vent
the trapped space within the ball or have a floating seat that vents
internally. This kind of ball valve is only found in high end aerospace
ball valves like Flodyne or Hydromatics, I think the later may be refunked
but their products can be found occasionally on the surplus market, great
valves with ball bearing trunnions on the ball.. I had a dozen of th 2 and
4".
Ken
On Thu, Jan 14, 2021 at 7:01 AM Brett Coles <brettcoles@xxxxxxxxx> wrote:
Hi all!
I'm sure this has been asked before, but I was recently reminded of the
concern of having a BLEVE when working with cryo-systems. We designed the
LOX feed system for our hybrid motor to have a rupture disc so that it
would vent pressure eventually if we lost valve control. However, I did not
account for the fact that 1,500 psi LOX boils at a significantly higher
temperature than atmospheric LOX. I am concerned that the LOX would warm up
then start to boil off and cause the rupture disc to function, then all
boil off at once when the pressure drops.
The chance of this happening is slight since the valve failure would have
to occur in a small window just before the motor fires and the pneumatics
system that controls the valves would have to lose pressure quickly enough
that by the time the controls system notices, there is not enough pressure
to open the vent valve.
The reason this is a concern is that we only bought double-acting
actuators rather than spring-return ones. I suppose we could add a check
valve and a surge tank to the vent valve to make sure it always has
pressure to operate. Do you think that could work?
Thanks,
--
Brett J. Coles
BYU Hybrid Rocket Team