Trill Steam Engine Indicator

Trill Steam Engine Indicator

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Usage conditions apply
The Trill Indicator Co. manufactured this steam engine indicator, serial number 27. It consists of a brass piston; a brass cylinder, which is open at top; an external, double wound spring, which can be changed; a large drum with a spiral spring and a single record; and a short lead pencil as stylus. Accompanying the indicator is a box with six springs, two drum springs, two wrenches, and three turn cocks.
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.
Currently not on view
Object Name
indicator, steam engine
Physical Description
brass (overall material)
wood (container material)
overall: 6 1/2 in x 11 1/2 in x 10 3/4 in; 16.51 cm x 29.21 cm x 27.305 cm
ID Number
accession number
catalog number
Credit Line
Gift from Estate of Kalman J. Dejuhasz, State College, Pennsylvania
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Work and Industry: Mechanical and Civil Engineering
Engineering, Building, and Architecture
Industry & Manufacturing
Data Source
National Museum of American History
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I am in possession of one of these devices ( Trill Indicator). It was given to me by my grandfather who worked on steam engines in Eastern Oregon during and after the Great Depression. It is still in its mahogany box, complete with an instruction book, and numerous readouts. Dates on readouts are from 1923-25

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