Hi,
I give you one scenario that will lead the valve to open.
Basically, the main target of the Cabin pressure unit is the comfort of passengers. So the best way is to handle the flight with a regular rate of 500 to 700 feet/minutes. That mean, from cabine cruise altitude (around 8000 feet) to ground level almost 15'
If you start descent from high altitude with very good rate, the plane could reach the cabin altitude, causing positive diferential pressure and opening your valve.
Today fuel saving purpose is a top priority for airlines and the good old descent with a 3° angle is not the best one to save fuel. We target a 4° descent, that mean, at 500 Kts a vertical speed of 3500 feet/minutes and less than 15' to get landed.
Rgds