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Live Steam Kits

When it comes to live steam loco building, the only available kit of which I am aware (as of July 2017) is one offered by Garden Railway Specialists for the GWR 2021 class pannier tank.

Reports suggest it is not an easy kit to assemble and that the power source, a geared steam "motor", is not very powerful, although there have been mixed reports. The power of an oscillator motor depends on the speed of rotation, this coupled with the step down gear provides the output to the power axles. Thus a fast revving oscillator coupled to a high ratio gearbox is the best option. They have the advantage of being simple and have no form of valve linkage.

If you are contemplating taking on one of these kits, I suggest you read the articles below before placing your order.

Construction notes 2021 Class tank


Improving the performance of the 2021 Class

The above article can also be downloaded as a PDF here

In the pipeline, although still some way from being available to purchase, is a kit for the LNWR 18 inch Goods (affectionately known as the "Cauliflower"). This will be a "proper" steam loco with two cylinders, connecting rods and "Joy" valve gear. Watch the Williams Models website for more details.

In the seminal work of P.Ransome-Wallis "The Illustrated Encyclopedia of World Railway Locomotives", he lists 34 different types of valve gear. However there is one type of valve gear that is simple and is looked on as somewhat "second class".

This is the humble Oscillator...

Most of us will be familiar with the Oscillator from the products of Mamod and the fact that several childhood steam engine are still running decades after -proves the robustness of the principle. Oscillators operate best at high speed -thus gearing them down is a priority...

This is the Oscillator supplied by Garden Railway Specialists for use with their GWR 2021 Class Pannier Tank.

It is available in this configuration;

  • 10mm bore with 5:1 reduction.

The Design Theory of Oscillator motors can be found in the Appendices section. You may wish to re-read the above articles after having studied it.

This is the Oscillator motor provided by Unit Steam Engines.

The bore is 8mm and the stroke is 19mm. The units may be linked together to provide various combinations and power pulse formats. The USE1 kit can be assembled in minutes. It runs on saturated steam at no more than 45PSI

Oscillators are not pretty but they can be used where steam motors would not normally be seen -or in fact were actually used in practice. The products of Sentinel Steam Works are an example -as is the BR Leader and the CIE CC1 "Turf Burner".

The "Bush Trams" of New Zealand used vertical steam engines and gears to drive wheels. The US logging geared locos such as Climax Type "A" and the early "Shays" are also suitable candidates for Oscillators. There have actually been std gauge locomotives with exterior mounted oscillator cylinders -rather than conventional valve gear.

How much power does an Oscillator develop compared to an electric motor?

If a SIMPLIFIED steam power formula is used (i.e. ignore Adiabatic and Isothermal effects)

  • 1 Bar = 100,000 Pascals = 100,000 Nm2 = 0.1 Nmm2
  • Area = (radius of bore mm x radius of bore mm x 3.142)
  • Energy = Area mm2 x Stroke mm x 0.1Newtons = J Joules per Bar pressure
  • Watts W = J Joules x Pressure in Bars x (RPM of Oscillator / 60 seconds)

In the case of the three cylinder Unit Steam Engine above running at 1000 RPM fed from a 3 Bar steam supply -it would develop 28.8 Watts. If this was geared down by 5 to 1 -then the output shaft from the gearbox would deliver 826.6 Grammes per Centimetre of torque at 200 RPM.

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Page last modified on March 19, 2018, at 08:45 AM