Indicator diagram: Optimal steam distribution

Company: Steam Technologies (small)Steam Technologies

Engineering Services & Rail Technology

Measuring steam engines or steam locomotives electronically and evaluate indicator diagrams


Economic viability by optimal valve setting within the steam engine

The correct operation of the valve gear is prerequisite for economical and low-wear operation as well as the full performance of a steam engine. This applies equally to steam locomotives, marine steam engines, but also to stationary steam engines.

Incorrect valve setting mean:

  • Poor running characteristic
  • Up to 20% lower performance
  • Significantly increased steam, fuel and water consumption
  • Bad steaming
  • Increased wheel slip tendency
  • Worse start up behaviour (countering)
  • Overloading of engine components and thus lower bearing life and increased risk of hot box and failure
  • Unnecessary stress on the structure (In extreme cases frame damage can be fostered)

These points, in addition to inconvenience to the staff, are a source of avoidable and sometimes significant additional costs for operation and maintenance. Even in today's heritage or tourist operation, therefore, the proper working of the steam engine should be taken into account in the interests of the most careful and economical operation as well as the avoidance of engine damage.

Indicator diagram: leaking piston valve

Leakage on a piston valve with bypass function

Indicator diagram: diverging clearance volumes lead to overly heavy compression

Unequal clearance volumes
(slide valve at 170 min-1)

Valve setting of the steam engine by using an indicator offers the most exact adjustment possibility. Adjusting by the sound of the exhaust beats or measuring with a cold machine does not allow a checkup of the result, does not detect the temperature-induced length extensions and is therefore only conditionally suitable.

The indicator diagrams, on the other hand, provide a deep insight into the mechanical and thermodynamic processes in the cylinder. Possible valve gear faults, leaks, valve damage as well as the correct dimensions of the clearance volumes can be reliably read from the diagrams. Thats why many railway departments required test runs with indicator after every extensive work on the motion, valvegear or the vales itself. In eastern Germany for example, this had been done consequently until the end of main line operation in the late 80s.

Benefit from the latest technology

The especially developed electronic indicator is superior to its mechanical counterpart in many respects

Some of the disadvantages of classical mechanical indicators are:

  • Complicated and time-consuming adaptation work for different loco types - thereby very expensive
  • Accurate adaption to the existing environmental conditions is necessary
  • Susceptible to measurement errors
  • Uncomfortable display and evaluation possibilities
  • Strongly limited system performance

In other words, valve setting of steam engines by means of mechanical indicators has long been outdated. Thanks to the digital measurement technology available today, it is possible to create a system which overcomes the weak points of the known, old system and also provides further diverse possibilities.

Taking indicator diagrams

An important component is the creation of meaningful indicator diagrams


Mounting the indicator onto your steam engine.



Measuring your steam engine during operation.



Evaluating the obtained measurement data.



Derive recommendations to optimise operations.



Simplified installation on any kind of steam locomotives and steam engines

The application of up-to-date measuring and evaluation technology has created a system that is quick and easy to install, which does not require time-consuming loco-specific adaptation work and is immediately ready for use.

With this "plug and play" solution, the time required for installation on any two-cylinder machine is less than an hour.

Example setup: Sensors installed at a cylinder on a steam locomotive


Fast and precise thanks to the electronic indicator

It was also possible to drastically reduce the effort required to record the indicator diagrams. By capturing and storing the measured data in real time, reasonable conclusions can be drawn about the quality of the steam distribution after only a few meters of test run.

System Performance

  • Piston stroke max. 730 mm (up to 1000 mm in future)
  • Pressure max. 20 bar (up to 40 bar possible on request)
  • Suitable for saturated and super heated steam
  • Practically unlimited number of measurements in a short time

Of course, the system is not limited to steam locomotives: the flexible device can be installed on every steam engine - whether it is on water or land, mobile or stationary.


Immediate evaluation of the obtained measurement data

A very important advantage is the evaluation of the measurements. If the small paper strips (which were still located on the writing drum immediately after a measurement) had to be measured, when a mechanical indicator is used, the evaluation software provides the possibility to immediately describe the pressure/stroke diagrams of the individual cylinder rooms immediately after a measurement on a laptop on the footplate.

Indicator diagram: optimised clearances for one cylinder
Rotation speed17,70min-1



The right decisions are made for a readjustment of the valve by special features and options in the graphics interface as well as by special computational operations. For example, the indicated work and the horsepower of each cylinder.

Evaluation Parameter

  • Creation of indicator diagrams / deviations between the cylinder rooms
  • Accurately determining the real cut off and the remaining valve times
  • Detection of maximum pressure
  • Calculation of average pressure
  • Calculation of indicated horsepower


Well-founded recommendations for valve setting

On this basis, a detailed documentation on the condition of the steam engine and its valve gear can be compiled after the test run. This demonstrably opens opportunities to reduce costs for maintenance or operation of the steam locomotive or the steam engine considered in each case.


Artful depiction: Indicator diagram with well balanced clearances overlays a single cylinder



Harzer Schmalspurbahnen GmbH

Reference: Harzer Schmalspurbahnen GmbH

Museumseisenbahn Minden

Reference: Museumseisenbahn Minden

Museumseisenbahn Hamm

Reference: Museumseisenbahn Hamm

Bayerischer Localbahn Verein

Reference: Bayerischer Localbahn Verein

Eisenbahn Tradition

Reference: Eisenbahn Tradition


We look forward to your inquiry!


Questions? Make a call!
(+49) 176 3265 3032


Send an e-mail.



Visit us on Facebook.



Send a fax.
(+49) 5224 6316