If tightened to the same torque, the Valve will always be in the same location.
Solution:
Measure the Pitch Thread distance (distance from one thread point to another).
Divide by 2 and add a washer that thick.
That would put the valve at 180 degrees to where it is now.
Example: Using 1/2"x16 thread
*) 1 inch divided by 16 equals .062"
*) .062" divided by 2 equals .031"
*) So, adding .031 to Washer thickness would turn the Valve 180 degrees.
Try and only use one washer to reduce the chance of leaks.