Krausch Engine Indicator Patent Model

This model was submitted to the U.S. Patent Office with the application for the patent issued to C. W. T. Krausch, of Chicago, Illinois, September 9, 1862, no. 36411.
The model represents an instrument designed to indicate and record speeds, draw-bar loads, boiler water levels, boiler pressures, steam-chest pressures, cylinder pressures, and conditions of the track connected with the operation of a locomotive engine and to plot these on a paper belt driven from a truck axle with a motion corresponding to the progress of the engine.
A series of levers and markers corresponding to the number of the above operations to be recorded works transversely on the paper record as the paper is advanced by the progress of the engine. The marker indicating speed is actuated by a spring-balanced bellows, the motion of which is determined by the volume of air delivered to it by small air-pump cylinders actuated by any convenient part of the engine. The other markers are actuated mechanically by a series of levers to various indicating instruments on the engine, not described.*
An engine indicator is an instrument for graphically recording the pressure versus piston displacement through an engine stroke cycle. Engineers use the resulting diagram to check the design and performance of the engine.
A mechanical indicator consists of a piston, spring, stylus, and recording system. The gas pressure of the cylinder deflects the piston and pushes against the spring, creating a linear relationship between the gas pressure and the deflection of the piston against the spring. The deflection is recorded by the stylus on a rotating drum that is connected to the piston. Most indicators incorporate a mechanical linkage to amplify the movement of the piston to increase the scale of the record.
When the ratio of the frequency of the pressure variation to the natural frequency of the system is small, then the dynamic deflection is equal to the static deflection. To design a system with a high natural frequency, the mass of the piston, spring, stylus, and mechanical linkage must be small, but the stiffness of the spring must be high. The indicator is subjected to high temperatures and pressures and rapid oscillations, imposing a limitation on the reduction in mass. Too stiff a spring will result in a small displacement of the indicator piston and a record too small to measure with accuracy. Multiplication of the displacement will introduce mechanical ad dynamic errors.
The parameters of the problem for designing an accurate and trouble free recorder are such that there is no easy or simple solution. Studying the variety of indicators in the collection shows how different inventors made different compromises in their designs.
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
Krausch, C. W. T.
place made
United States: Illinois, Chicago
associated place
United States: Illinois, Chicago
overall: 8 7/8 in x 11 7/8 in x 11 3/4 in; 22.5425 cm x 30.1625 cm x 29.845 cm
ID Number
catalog number
patent number
accession 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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