Granted Patent
Utility
US 4,444,398 · App. 06/468,333
Self-activating ferrofluid seal apparatus and method
Inventors:
Thomas J. Black, Jr., Philip Stahl
Patented Case
View Patent ↗
Granted: Apr 24, 1984
Filed: Feb 22, 1983
Inventors
Thomas J. Black, Jr.
Philip Stahl
Assignee (at issue)
Ferrofluidics Corporation
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.