Frank’s Patent Model of an Opposed Piston Steam Engine - 1875


This model was filed with the application to the U.S. Patent Office for Patent Number 169,249 issued to Samuel B. Frank of Marshall, Missouri on October 26, 1875. The patent was for an opposed piston steam engine with four pistons. The goal of the design was to reduce vibration caused by unbalanced reciprocating masses.

The four pistons were equally spaced within a single cylinder, and each cylinder traversed one fourth of the length of the cylinder. The two inner pistons were arranged to move towards each other while the outer pistons would move away from each other. The reverse order would take place on the next cycle. A single slide valve with multiple ports fed steam to the appropriate volumes between the pistons. Each piston had its own crosshead, two on the left of the engine and two on the right. Concentric piston rods were used to allow the rods for the outer pistons to pass inside those for the inner pistons.

The use of the two pairs of opposed pistons was claimed to reduce vibration, and Frank also claimed the engine would be more powerful than standard engines. As shown in the image the design was complex and had many moving parts and wearing surfaces. It is not known how practical the design was to manufacture and operate. A search of available literature did not produce any examples of actual use of the patent.

The patent model is made of brass and mounted on a wood base. It is highly detailed and illustrates all of the key details of the patent. A full description of the operation of the engine along with complete diagrams of the patent can be found in the patent document online at the United States Patent and Trademark Office website,

Date Made: ca 1870Patent Date: 1875-10-26

Inventor: Frank, Samuel B.

Associated Place: United States: Missouri, Marshall

Subject: Patent ModelsSteam Engines


See more items in: Work and Industry: Mechanical and Civil Engineering, Engineering, Building, and Architecture, Patent Models

Exhibition: Power Machinery

Exhibition Location: National Museum of American History

Credit Line: Gift of D. C. Public Schools, Department of Science, Washington, D. C.

Data Source: National Museum of American History

Id Number: MC.321889Accession Number: 245986Patent Number: 169,249Catalog Number: 321889

Object Name: engine, steam, double opposed piston, Frank, 1875patent model, engine, steam

Measurements: overall: 6 in x 8 in x 14 in; 15.24 cm x 20.32 cm x 35.56 cm


Record Id: nmah_846153

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