Mantei is closing, not Valverde. But if/when Mantei is injured or dealt, Valverde would step into the closer role. He was an amazing K/9 last year (2nd in the majors to Gagne), and if given the chance I'm sure he would be a great closer. Throughout the minors he K'd a lot of people as well, so it wasn't a fluke.
"Jack, will you call me, if you're able?"
"I've got your phone number written, in the back of my Bible."