A dab of Petrol Gel to the O-Ring under said nut is helpful in prolonging the life of the o-ring.
The needle should be opened completely, then closed a couple of turns so the needle protrudes slightly beyond the orifice so when lime/scale builds up around the needle it can poke through and close.
If the final step is ignored, the valve may not operate properly after a very short time-depending on water conditions-and is thus installer error.
