Here, the P-D Valve is set up and ready for use. The clear tube is connected to a pressure gauge. Also notice the height standard between the ball detent and the locking collar. The locking collar is put in place with the height standard in place, then the standard is removed and the collar pushed down until it contacts the top of the ball detent. Now you know the valve is open exactly 0.400-inch (the height of the standard).