H8: 1907 through 1913; H9: 1913, 1914; H10: 1913 through 1916
H8: 480; H9: 274; H10: 273
Externally, there was little differences between the three classes. The main differences were the cylinder bore sizes (24" for the H8, 25" for the H9, and 26" for the H10), which is hard to tell apart in our scale models.
On the Chartiers branch these were used for heavier freight. They were probably the second most-often-seen engine type on the branch. The H10 class was primarily built for the PRR's Lines West, and so that will be my personal focus.
PRR #7688 (H10) is one of the models preserved, and was added to the National Register of Historic Places in 1979. It is kept at the Railroad Museum of Pennsylvania near Strasburg, PA.