Granted Patent
Utility
US 5,339,864 · App. 08/094,513
Safety sub for retaining drilling fluids
Inventors:
William L. Carbaugh, Douglas W. Carlson
Patented Case
View Patent ↗
Granted: Aug 23, 1994
Filed: Jul 20, 1993
Inventors
William L. Carbaugh
Douglas W. Carlson
Assignee (at issue)
Hydril Company
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.