Shut off valve -Caleffi auto feed

Hello

I had a Caleffi 553 Autofil valve installed on my gas boiler and set at 19 psi in the summer to replace the old faulty one. I think that might be too high given my house is maybe 20 feet from the water valve to top of highest rad. My question is for the shut off valve on the back of it - is that supposed to be opened or closed and I turn towards the + or - ?

Thanks