Joost,
We delivered the attached valve to our customer who passed the valve to install Rotork actuator. When the Rotork distributor fit the actuator and manually tested it, the valve jammed when he opened about 20% only.
Now the valve with bare stem was returned to us to check, do you have any suggestion to check what is the root cause ? We might have to send it to our qualified workshop but we will instruct them to follow your instruction if you had one.