Gas Engine Indicator

Description
This De Juhasz gas engine indicator, serial number 407, consists of a small steel piston with three grooves; a vented brass cylinder with radial fins for cooling; an external, double wound spring, which can be changed; a light Bakelite drum with a spiral spring and a single record; and a metal stylus. This is a new instrument, complete with metal box and accessories.
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.
Location
Currently not on view
Object Name
indicator, gas engine
Physical Description
brass (overall material)
bakelite (overall material)
Measurements
overall: 6 in x 12 1/4 in x 9 3/8 in; 15.24 cm x 31.115 cm x 23.8125 cm
ID Number
1981.0217.01
accession number
1981.0217
catalog number
1981.0217.01
subject
Engineering, Building, and Architecture
Work
Industry & Manufacturing
Indicators
See more items in
Work and Industry: Mechanical and Civil Engineering
Indicators
Data Source
National Museum of American History, Kenneth E. Behring Center
Credit Line
Gift from Estate of Kalman J. Dejuhasz, State College, Pennsylvania

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