Signed by the Astros as an amateur free agent out of the Dominican Republic in 1979, Julio Solano is your prototypical quad-A pitcher. He spent five seasons in Houston pitching primarily in a relief role for the Astros. In his time with Houston he compiled a 4.55 ERA, and a 78 ERA+, in 142.1 innings.
Now a 78 ERA+ is below average, but that doesn't mean he didn't provide the Astros with productive innings. In fact in 1984 he had quite possibly one of the best years for an Astros reliever in terms of ERA+. In 50.2 innings he posted an ERA of 1.95 and an ERA+ of 171. He followed that up with a 101 ERA+ in 1985, in 33.2 innings. Those two years were flanked by ERA+ of 61, 48 and 52, although, those were also the years he pitched the least innings.
The other interesting thing to note about Solano is that he spent every year with the Astros in the Minor Leagues at some point during the seasons, hence the quad-A tag. Down there he typically switched between pitching out of the bullpen and the rotation. Looking at his Minor League track record you have to wonder if the Astros rushed him to the majors.
He pitched rookie ball in both 1980 and 1981. He moved up to A ball in 1982 and then made a huge jump from A ball to the Major Leagues; his Major League debut was April 5, 1983. After struggling in Houston he was sent down to AAA where he would spend his career taxing back and forth between AAA and the big leagues. Still going from A ball to the Major Leagues back to AAA seems like a weird jump for a young pitcher.
Then again looking at his Major and Minor League peripherals shows us that he walked almost as many guys as he struck out. That's going to limit your success in professional baseball.