Lehmann & Michels Gas Engine Indicator


Lehmann & Michels manufactured this gas engine indicator in Germany. According to a card inside the box, this style of indicator was invented by Voelcker about 1928. It consists of a steel piston with one groove, a vented brass cylinder; an external, double wound spring, which can be changed; a small aluminum drum and single record. There is an additional device to turn the drum by a steel handle that is driven from the crank or cam shaft. Accompanying the indicator is a box with tools, one spring, extra parts, a pad of paper, and product literature.

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

See more items in: Work and Industry: Mechanical and Civil Engineering, Engineering, Building, and Architecture, Work, Industry & Manufacturing, Indicators


Exhibition Location:

Credit Line: Gift of estate of Kalman j. Dejuhasz, State College, Pennsylvania

Data Source: National Museum of American History

Id Number: 1981.0217.11Accession Number: 1981.0217Catalog Number: 1981.0217.11

Object Name: indicator, gas engine

Physical Description: wood (case material)brass (overall material)steel (overall material)paper (overall material)Measurements: overall: 5 1/4 in x 11 5/8 in x 10 7/8 in; 13.335 cm x 29.5275 cm x 27.6225 cm

Guid: http://n2t.net/ark:/65665/ng49ca746a6-6ac6-704b-e053-15f76fa0b4fa

Record Id: nmah_847292

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