Granted Patent
Utility
US 4,282,831 · App. 05/959,726
Back flow check and self-cleaning spring biased waterer valve
Inventor:
Norman P. Nilsen
Patented Case
View Patent ↗
Granted: Aug 11, 1981
Filed: Nov 13, 1978
Inventor
Norman P. Nilsen
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.