Granted Patent
Utility
US 4,936,397 · App. 07/328,890
Earth drilling apparatus with control valve
Inventors:
William J. McDonald, William C. Maurer
Patented Case
View Patent ↗
Granted: Jun 26, 1990
Filed: Mar 27, 1989
Inventors
William J. McDonald
William C. Maurer
Assignee (at issue)
Slimdril International 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.