Thompson and Hunt’s Patent Model of a Shaft Governor – 1878

Thompson and Hunt’s Patent Model of a Shaft Governor – 1878

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This model was filed with the application to the U.S. Patent Office for Patent Number 204,924 issued to Joseph W. Thompson and Nathan Hunt of Salem, Ohio on June 18 1878. The patent was for an improved design for a steam engine governor. This patent was based on a previous design by Thompson (Patent Number 162,715 of April 27, 1875).
This type of governor is intended to be mounted on the shaft of the engine and to vary the cut-off of the steam valves in order to control speed. The image of the governor shows two weights, each on a pivoting arm and secured by springs. As the governor case rotates the weights are extended outwards by centrifugal force against the tension of the springs. Pushrods attached from the pivot arms to a collar on the shaft move the relative position of the eccentric around the shaft. The eccentric is the offset circular plate shown at the end of the central shaft. The eccentric provides lateral motion to control the steam valves, and its relative position on the shaft thereby controls the timing of when the valves are closed.
Thompson’s earlier patent (Number 162,715 of April 27, 1875) had most of these key elements. The improvements made in this patent consisted of using ball and socket joints to connect the rods to the eccentric and adding stop pins mounted in cushioned slots to prevent damage caused by sudden speed changes.
Shaft governors of this design were used in the successful high speed Buckeye Engine. Both this and the earlier Thompson patent were assigned by the inventors to the Buckeye Engine Company of Salem, Ohio.
The patent model is constructed of brass and steel. All of the key elements of the patent are illustrated by the model. A full description of the operation of the governor along with complete diagrams of the patent can be found in the patent document online at the United States Patent and Trademark Office website,
Object Name
governor, shaft type, model
governor, shaft type
patent model, governor, steam engine
date made
patent date
Thompson, Joseph W.
place made
United States: Ohio, Salem
associated place
United States: Ohio, Salem
steel flywheel: 6 in; x 15.24 cm
ID Number
catalog number
accession number
patent number
Patent Models
Steam Engines
See more items in
Work and Industry: Mechanical and Civil Engineering
Patent Models
Engineering, Building, and Architecture
Power Machinery
Exhibition Location
National Museum of American History
Data Source
National Museum of American History
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