Can you enlighten my, how that key is working? It doesn't look like a common trombone water key, and that's spyrale spring...what's up with that?
It's a curved rod within a curved tube. Look closely at where the spring ends and you will see the curved inner rod. Press the knurled knob at the spring end (barely visible in pic) and it lifts the cork up and away from the nipple allowing the water to drain.