Modern Steam Engines

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Steam Engines – Part One: Links to models and other Trivia

The steam engine has always been a marvel to most people. Incredible torque from standstill but also pulling Goliath locomotives to well over 100 m.p.h.  The first engine powered locomotive was developed well over 200 years ago. What makes them so special?  What is the secret to their success and more importantly why do modelers the world over always seem to lean towards building their own engine?

Thomas Horn Beam engine at the Bredgar and Wormshill Light Railway
Thomas Horn Beam engine at the Bredgar and Wormshill Light Railway – Image by wiki commons Admin MJ Roots

Safety Margins


Although that simplistic looking reciprocating engine is always looked upon in awe there are two things that us newbies forget, the first steam engines were not built with modern tooling but yet their parts were machined to perfection – the engineers of the time, many just craftsmen were every bit as good as today – in fact maybe better. The physics involved in building a practical machine,  as a prime mover or show piece is not for the feint hearted. Ask any engineer about boiler safety, boiler design and the inevitable accident when we forget to utilise proper safety margins. The Mississippi River can bear testament to the many steam powered boats and ships that had catastrophic boiler failure and subsequent loss of life. So what makes a steam engine so special, why are we prompted to build something which most of the technical geeks today feel is nothing better than an archaic relic of a bygone era?

Your basic steam engine design would consist of nothing more than a pressurised vessel, a piston, valve or port and a flywheel.  This engine may be a single acting or double acting steam engine, the difference being in that a double acting steam engine has alternating pressure on both sides of the piston, whereas single acting would normally be only on the crown of the piston with the momentum of the flywheel pushing the piston through to the next power stroke.  The models of these engines often needed to be manually started. Single acting engines were most often seen in the form of a Beam engine which was used as a water pump to drain mines and canals. There are lots of informative articles based on this type of engine.

Animated Engines


Along came the oscillating steam engine which is a double acting engine.  A simple engine yet brilliant in design.  A great place to see an animated engine is the ultimate in animated websites –  – the engine has two ports to allow pressurised steam to create the downward or upward stroke.  This article however is not about how steam engines work, there’s enough information on the web covering this – more so we want to cover companies that supply working plans, kits and parts. We will move from pressurised boilers which every single model maker will warn you against making to mono-tube boilers or flashboilers.

As an aside, my first model steam engine was bought as is, passed down through two generations. It had a safety valve which we now know was never tested and we now know could have been pretty dangerous. As a six year old I was not allowed to run this engine if my father wasn’t supervising. Anyone believe a 6 year old would be a responsible adult at any time and heed this advice?  Of course we tried different heating experiments and luck more than being informative played a role in never having any major disaster while playing with this engine.  These reciprocating engines now have one very common problem – absurdly costly. I saw one recently, albeit a far more modern version costing about U$300.00.


Geoff Wolfe 

Early reciprocating steam engines were notoriously inefficient.  Geoff Wolfe has a very informative website and an article which is excellent in that it is thought provoking to the layman is his post on Compression Ratio and Break Mean Effective Pressure. We all know that diesel engines are far more efficient than your normally aspirated gas or petrol engine but why is this? There are some decently written articles about compression ratio etc but it’s in the context of monotube / flashboiler engine design that makes this article thought provoking. More on this later.

The Cyclone

The flashboiler supplies an almost immediate source of pressure – it was used in motor cars and subsequently model hydroplanes. They are very efficient and currently there are many designs been used which are supposedly green. I use supposed because it all depends on the heat source and how the exhaust emission is controlled. One such design is the Cyclone. I am going to plagiarise here and add the following from the website:  “Cyclone Technologies LLP, developer of the Cyclone external combustion engine, received an Automotive Engineering International (SAE’s publication) Tech Award at the SAE World Congress in Detroit.

The Cyclone modifies the traditional Rankin cycle steam engine to deliver the use of super-critical pressure (3,200 psi) and super-heated steam (1,200° F)—normally found in high-efficiency electrical power plants—in an efficient, compact package suitable for a vehicle.”

The Cyclone is an external combustion engine. External combustion engines, like electric motors exhibit extremely high torque at very low RPM. Ever think why an electric motor driven car from pullawaycan spin wheels without a clutch – or gearbox? Straight coupling between engine and wheels. Steam locomotives and ice breakers spring to mind. The Cyclone can run on any fuel, it doesn’t need a clutch as it’s highest torque is at lowest RPM, it is double the efficiency of a gas (petrol) engine and a three cylinder device is self starting. Is it a breakthrough? Somebody had the genius to build this engine, Harry Schoell, surprising enough the information was all there, it took just one person to put the plan together. So from steam to internal combustion petrol and diesel engines back to external combustion. This is not crackpot – read about the gentleman here.  I am sure most Parts-Ring readers will not be familiar with Cyclone Technologies, neither was I until last year when searching for something greener, modern bio-fuel run engines and what to do with the waste. Of course elsewhere we wrote about hydrogen fuel cells – I think the “Schoell Cycle Engine”  may be just that tad more innovative.  Watch their space.


Possibly one of the best websites with regard to their kit range and quality would be Stuart Models.  Stuart Models also have a comprehensive catalogue covering gas burning boilers and pumps to make your desktop model work.

Chasteam is a great website. I loved their kit range – I have no idea of the final build quality but their pricing is awesome. A definite visit for the modeller  – please visit their website.

The CEDesign website gives a comprehensive list of companies manufacturing model kits. We can only wish that we had so much more money hidden in the piggy bank.

Build your Own

There are three websites which give considerable information,

One of the most popular websites in the universe, Instructables has a few plans – this one is a cheap and simple unit designed to run on compressed air. In fact all the models on these pages, when built from a kit are designed for compressed air – this does not mean you should not build a boiler, it just means that we distance ourselves from your attempts at possibly hurting or God forbid killing yourself.

County College of Morris Engineering – Tech Department, by N.J. Randolph – lots of plans which will get your creative juices flowing.

Over 120 free plans for steam engines at John-Tom’s website. Includes plans from Mr. Elmer Verburg – see also Amazon:

Avery nice forum for the modeller – – some worthy advice from participating members, some great builds and yes, do get yourself a milling machine. At Parts-Ring we do believe that the prices of these will go down as Chinese imports pick up up but be careful – try before you buy. I have heard some really bad stories, you get what you pay for. Read our parent article on CNC.

Reading Material

The electronics industry has in most parts made our internal combustion engine more efficient – I will not say more reliable because diesel engines have always been reliable. We add more and more sensors, more and more feedback systems – all to improve efficiency. The external combustion engine has not had the privilege of been seen as a technological marvel except in the 1700’s – but yet, having said that are we not heading in the wrong direction. Many innovative thinkers do believe so, the Schoell Cyclone engine is a case in point.

Green Steam Website

Interesting fact, most steam engines can be made green – it all depends on what you are using as fuel.

The Green Steam Engine website is an interesting one. Advantages are plenty – the flexible rod transmission system, patented by Robert Green is shown in numerous photos and videos.


There have numerous queries with regards to this motor – it has been around for many years yet interest is pretty miserable.

Sterling Motor

Below is a tube video of a Sterling Motor.



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