Granted Patent
Utility
US 4,318,420 · App. 06/192,922
Ball valves
Inventor:
Michael A. Calvert
Patented Case
View Patent ↗
Granted: Mar 9, 1982
Filed: Oct 1, 1980
Inventor
Michael A. Calvert
Assignee (at issue)
T K Valve Limited
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.