In article ,
says...

Jeff Findley wrote:

Note that on this diagram, there is no isolation valve in the helium
plumbing between the check valve and the NTO tank. The gas isolation
valves are between the check valve and the helium tank.

So the arrangement that SpaceX used is not new. That's why they said
that what they encountered was "unexpected". The space shuttle flew
dozens and dozens of times without this happening.

Perhaps it did happen, but the valve didn't explode because the helium
pressure was lower.

The valve reportedly failed due to forcing liquid through the valve at
extremely high pressure. This happened when they opened the upstream
helium valves to pressurize the propellant tanks for the Super Draco
engines to fire. That liquid was not supposed to be upstream of the
check valve, so the check valve was simply not designed to handle high
pressure liquid being forced through it.

Jeff
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