What is the part above the ball valve? What does it do?
Looking at, say, Home Depot (no relation, just a handy link) one sees pretty much the exact same thing.
The data sheet clearly indicates that the lower ‘bump’ is for the inlet strainer, the bell shaped bit above is the pressure regulator.
I have one on the inlet to my house. I live directly down hill from a large city water tank, and the water pressure on a hose bib at the far corner of the house from the supply pipe was over 100 psi, well above the max pressure rating of, well, anything in the house. Adjusting the screw at the right of the picture adjusts the outlet pressure to something more reasonable.