Jorge R. Frank wrote:

No, I'm thinking about the valve. The consensus is that the separation
event caused the valve to fail.

The primary set of explosive bolts to separate the orbital module from
descent module failed to fire.
When the back-up set fired it also caused the primary set to fire at the
same time causing a violent shock and the pressure valve to open.
At least that's the official story....but before this happened the
cosmonauts were having trouble sealing the descent module hatch, and a
indicator light was indicating it was not properly closed.
They asked mission control what to do, and were told to keep tightening
it up (it uses a wheel type crank to close it, like a watertight door)
till the light indicated it _was_ sealed, even though that was tighter
than you were supposed to torque it, and not worry about it.
Then when the modules separated the air leaked out.
So if the hatch still wasn't properly sealed, saying it was a pressure
equalization valve that opened got mission control off the hook for the
cosmonaut's death.

Pat