Some knee jerk reaction time you have in borneo Blackie, I did the A320 course 10 years ago, it had the 4th bearing scav valve even then.
The function of the valve is to restrict the scavenge line from the 4th bearing at high N2. The reason for this is, at high N2 and thereby high oil press, the oil "flushes" through the bearing compartment and does not remove enough heat. The restriction slows down the oil and it removes more heat.
Hopes this helps.
Cheers
Doc