Johnston Air Compressor, Patent Model

This model was submitted to the U.S. Patent Office with the application for the patent issued to William Johnston, of Washington, DC, November 4, 1879, no. 221318.
The compressor represented by the model is in effect a bellows. It is constructed as a cylindrical casing mounted upon a stationary horizontal shaft about which it oscillates. Two diaphragms extend in radial planes from the inside and top of the casing to a bearing on the upper side of the shaft. The space between these diaphragms is wedge-shaped. The two spaces thus formed are valve spaces, inlet and outlet, respectively. Flap valves are let into the diaphragm connecting the valve spaces with the lower part of the casing interior. A third diaphragm, called a lug, is fixed to the underside of the shaft and extends downward to the cylinder casing.
In use the casing is filled with water to the level of the center of the shaft. When the case is rocked the water is held approximately stationary by the lug and the air between the surface of the water and the diaphragm on the down side is compressed while a partial vacuum is formed in the space between the surface of the water and the diaphragm on the up side. The compressed air escapes through the outlet valve and air is drawn into the up side through the inlet valve. As the casing is rocked back and forth it is in effect a double-acting bellows.
This description comes from the 1939 Catalog of the Mechanical Collections of the Division of Engineering United States Museum Bulletin 173 by Frank A. Taylor.
Currently not on view
date made
patent date
Johnston, William
place made
United States: District of Columbia, Washington
associated place
United States: District of Columbia, Washington
Physical Description
wood (overall material)
overall: 9 3/8 in x 10 1/8 in x 9 in; 23.8125 cm x 25.7175 cm x 22.86 cm
ID Number
catalog number
accession number
patent number
See more items in
Work and Industry: Mechanical and Civil Engineering
Industry & Manufacturing
Bulletin 173
Engineering, Building, and Architecture
Data Source
National Museum of American History


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