Granted Patent
Utility
US 4,889,199 · App. 07/054,713
Downhole valve for use when drilling an oil or gas well
Inventor:
Paul Bernard Lee
Patented Case
View Patent ↗
Granted: Dec 26, 1989
Filed: May 27, 1987
Inventor
Paul Bernard Lee
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.