Granted Patent
Utility
US 4,838,355 · App. 07/242,747
Dual hydraulic safety valve
Inventors:
Dwayne Leismer, William A. Blizzard, Jr.
Patented Case
View Patent ↗
Granted: Jun 13, 1989
Filed: Sep 9, 1988
Inventors
Dwayne Leismer
William A. Blizzard, Jr.
Assignee (at issue)
Camco 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.