Sons Dodge Dakota has no power steering??

Ok, my son has a 2000 Dodge Dakota 4.7, 2 wheel drive. He came home about a week ago and said he has no power steering. So we replaced the pump. About a week later it happened again. I looked at the fluid and there was metal savings in it. I thought it was the rack that had gone bad, so we replaced that along with a new pump again. We cleaned out all the lines including the cooler, put everything back together, bled the system had power steering for about 5 minutes and we have nothing again.!!
I told him to get another pump since its under warranty and we'll try it again. Any thoughts of what the issue could be?? Does anyone know what the pressure switch does in this system?

We just don't want to keep spending money, not knowing what the issue is! :sSig_thanks:
Author: 66sportfury