Answewr 1:
It' was not clear for me the definition of Ball valve like a Plug valve.
To close the "plug" you will apply torque and increasing torque you can increse the seats thightness.
In case of ball valve you can't increse thightness incresing torque. like wedge gate and in some cases also...
Question 1
In the Table F.1 of API 6A annex F, there is the column with Allowable leakage usefull for some kind of valves like gate plug and check, but there isn't reference to the ball valves...
- ??? We can assume ball valves as a check valves, because the closure parts (seats and ball)...
