Granted Patent
Utility
US 4,878,550 · App. 07/219,394
Pilot-valve-controlled percussion drilling tool
Inventor:
Jo-Yu Chuang
Patented Case
View Patent ↗
Granted: Nov 7, 1989
Filed: Jul 15, 1988
Inventor
Jo-Yu Chuang
Assignee (at issue)
Sandvik Rock Tools, Inc.
This patent predates the USPTO's electronic file wrapper — prosecution documents from this era exist only in the Patent Office's paper records. A certified copy of the file history can be ordered from the USPTO's paper archives.