Granted Patent
Utility
US 4,283,039 · App. 06/156,833
Annular blowout preventer with upper and lower spherical sealing surfaces
Inventors:
Gary R. Schaeper, Richard A. Olson
Patented Case
View Patent ↗
Granted: Aug 11, 1981
Filed: Jun 5, 1980
Inventors
Gary R. Schaeper
Richard A. Olson
Assignee (at issue)
NL Industries, 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.