Knox Hydraulic Pump Slide Rule

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This rule consists of a clear plastic envelope, glued together along the back bottom edge, and a white plastic slide. The front is marked: KNOX (/) SO. WALPOLE/W. SPRINGFIELD. MASS./BRIDGEPORT, CONN. (/) PNEUMATIC & (/) HYDRAULIC SYSTEMS & (/) COMPONENTS. By setting the force in pounds opposite the PSI of a line, a user can read the diameter of a cylinder in inches. By setting the rule to the desired diameter of a cylinder, the user reads the displacement in cubic inches opposite the length of a stroke in inches. By setting the back of the rule to a desired pump delivery in gallons per minute, the user reads the time in seconds opposite displacement in cubic inches and the velocity of oil flowing through the pipe (in feet per second) opposite the area of the pipe in square inches.
Knox, Inc., manufactured hydraulic pumps. From its headquarters on Foxhill Drive in South Walpole, Mass., the company filed for trademarks in 1966 and 1968 and was assigned U.S. Patent 3,599,849 in 1971. Thus, this rule likely dates to around 1970. By 1980, the company was renamed Knox-Norton, Inc., and headquartered in Hartford, Conn.
Reference: U.S. Patent and Trademark Office, Trademark Electronic Search System.
Currently not on view
date made
ca 1970
Knox, Inc.
place made
United States: Massachusetts, South Walpole
Physical Description
plastic (overall material)
overall: .1 cm x 16.5 cm x 7 cm; 1/16 in x 6 1/2 in x 2 3/4 in
ID Number
accession number
catalog number
Credit Line
Gift of Pratt-Read Corporation
Rule, Calculating
See more items in
Medicine and Science: Mathematics
Science & Mathematics
Slide Rules
Data Source
National Museum of American History


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