Granted Patent
Utility
US 4,571,302 · App. 06/687,975
Relieving pressure differential in vacuum filter
Inventor:
David H. Willson
Patented Case
View Patent ↗
Granted: Feb 18, 1986
Filed: Dec 31, 1984
Inventor
David H. Willson
Assignee (at issue)
AMSTED INDUSTRIES INCORPORATED
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.