Outside Spring Steam Engine Indicator with Lanza Attachment for Continuous Recording - 1930

Outside Spring Steam Engine Indicator with Lanza Attachment for Continuous Recording - 1930

<< >>
Usage conditions apply
An engine indicator is an instrument for graphically recording the cylinder pressure versus piston displacement through an engine stroke cycle. Engineers use the resulting diagram to check the design and performance of the engine. The indicator portion of this unit is a 1930 Crosby Valve and Gage company external spring model. The advantage of the outside spring was isolation of the spring from the varying temperatures inside the cylinder. The continuous recording attachment was invented by Professor Gaetano Lanza of MIT and patented in 1908.
The advantage of continuous measurements is that accurate assessments can be made of engines which experience widely varying loads during portions of their work. A continuous recording mechanism had been patented by T. Davidson approximately a year prior to the Lanza patent. Lanza’s improvement was the replacement of cords attached to the engine’s piston rod with a rigid metal attachment. This eliminated errors and distortions caused by the cord stretching and variations in the return springs.
The introduction of the steam indicator in the late 1790s and early 1800s by James Watt and others had a great impact on the understanding of how the steam behaved inside the engine's cylinder and thereby enabled much more exacting and sophisticated designs. The devices also changed how the economics and efficiency of steam engines were portrayed and marketed. They helped the prospective owner of a machine better understand how much his fuel costs would be for a given amount of work performed. Measurement of fuel consumed and work delivered by the engine was begun by Watt, who in part justified the selling price of his engines on the amount of fuel cost the purchaser might save compared to an alternate engine.
In the early days of steam power, the method to compare engine performance was based on a concept termed the engine’s “duty”. It originally was calculated as the number of pounds of water raised one foot high per one bushel of coal consumed. The duty method was open to criticism due to its inability to take into consideration finer points of efficiency in real world applications of engines. Accurate determination of fuel used in relation to work performed has been fundamental to the design and improvement of all steam-driven prime movers ever since Watt’s time. And, the steam indicators’ key contribution was the accurate measurements of performance while the engine was actually doing the work it was designed to do. This indicator is the result of nearly 150 years of design and performance improvements. The Lanza attachment enabled accurate and continuous of monitoring of engines that experienced widely varying load conditions.
Object Name
indicator, outside spring
date made
place made
United States: Massachusetts
ID Number
catalog number
accession number
Credit Line
Gift of Crosby Steam Gage & Valve Co., Boston, MA.
Steam Engines
See more items in
Work and Industry: Mechanical and Civil Engineering
Measuring & Mapping
Engineering, Building, and Architecture
Power Machinery
Exhibition Location
National Museum of American History
Data Source
National Museum of American History
Nominate this object for photography.   

Our collection database is a work in progress. We may update this record based on further research and review. Learn more about our approach to sharing our collection online.

If you would like to know how you can use content on this page, see the Smithsonian's Terms of Use. If you need to request an image for publication or other use, please visit Rights and Reproductions.


Add a comment about this object