KRAMER’S Short Typology of Model Steam Engines
On this web-site several different types of model steam engines are mentioned and talked about, namely Oscillating Engines, Piston Valve engines and Slide Valve Engines with Reversing Gear.
- All very well, but what does all that really mean?
- And what are the advantages or disadvantages of the different types?
- Which type would suit my needs best?
I hope to answer these questions with following KRAMER’S Short Typology of Model Steam Engines about the three most common types of model marine steam engines.
1. Oscillating Engines
2. Piston Valve engines
3. Slide Valve Engines
1. Oscillating Engines
Reversible, with double acting Cylinders
The engines shown below are not from our range of products.
- The most remarkable point about the construction of oscillating engines is that their cylinders are designed to be moveable. Their piston rods are directly connected to the crank shaft, this causes the cylinders to oscillate around a pivot point.
- This oscillating movement of the cylinders regulates and times the distribution of steam to the cylinders.
- Regulating the speed, stopping and reversing the engine is done with a Reversing Valve.
- Simple construction, relatively few components and therefore robust, simple to use and to maintain. In addition they are usually found to be in the lower price range.
- Often very compact. Due to the lack of connecting rods they tend to stand somewhat lower then other types. Engines with a V-configuration are also very short which makes them particularly well suited for smaller model boats.
- RC-control of these engines is easy since it requires only one servo to regulate speed, stopping and reversing.
- For the same reasons also suitable for models with twin screw installations.
- Oscillating engines as models have very little similarity’s with original engines.This is particularly noticeable when used in open launches.
- This particular design runs less efficient then the others due to having more internal friction and a strong inclination to steam leakages.
- Starting from cold they tend to fling considerable amounts of oil and condensed water around them. But this phenomena is considerably reduced after the cylinders have warmed up sufficiently.
- A ‘clean’ model engine room is with this type of engine practically impossible.
2. Piston Valve Engines
with Reversing Valve
The construction of this type of engine bears a much closer resemblance to the original steam engines.
- The cylinders are solidly fixed to the engine frame and do not move. The power of the pistons is transmitted to the crank shaft by the proper arrangement of piston rod, cross head and connecting rod.
- The steam distribution to the cylinders is regulated by separate valves. These valves are moved and timed by eccentric sheaves fitted to the crank shaft.
- The valves are cylindrical in shape and run in corresponding bores within the cylinder blocks. That’s the reason why they are called ‘Piston Valves’.
- This type of valve gear permits to control the engine with a reversing valve to regulate speed, to stop and to reverse with the same ease as oscillating engines.
- The valve gear is apparently relatively simple, basically something “round running in a hole” but there are hidden points which make all the difference between a good and efficient engine and a “scrappy” one which wastes a lot of steam without producing much power!
- Firstly, piston valves must be fitted very carefully and tightly to their bores (it is best to grind them in) otherwise the engine will run hopelessly inefficient.
- Secondly, the choice of material is also very important, a piston valve made of brass running in a brass cylinder block will result in rapid wear and loss of efficiency because when brass rubs on brass it simply grinds it self to dust!
In our piston valve engines JADE, GEM TM1, QUARTZ Vertical, QUARTZ Vintage and QUARTZ Horizontal we use only the optimal pairing of materials, namely stainless steel valves ground in to the bores of the brass cylinder blocks, therefore guaranteeing a long and useful live for our engines.
- This type of model steam engines bears a much closer resemblance to the original marine steam engines and is therefore very well suited for open steam launches.
- Engines with piston valves and reversing valve require only one servo to fully control the engines speed, stopping and reversing.
- Naturally such engines are very well suited for models with twin screw installations, particularly if it is desired that the engine room should look like the real thing!
- Piston valves engines do not cause such a mess like those oscillators. Our range of engines with piston valves start and run practically drip free, your engine room stays therefore much cleaner!
- When starting up from cold piston valve engines have a tendency to block or run a bit rough during the warm up phase because they can not get rid of the condensed water water as easily as oscillating engines.This will stop after the engine has warmed up sufficiently.
- With piston valve engines where precision and choice of material have been given less then due care and attention such engines tend to suffer a certain loss of efficiency and power over time.
3. Slide Valve Engines
with mechanical Valve Gear
And now we have reached the top class of Marine Steam Engine Models. These engines compare very closely in looks and function to the original steam engines with all their complex, constantly moving eccentric sheaves, levers and links. It’s pure poetry in motion!
- The cylinders are solidly fixed to the engine frame the same way as the piston valve engines are. The power of the pistons is transmitted to the crank shaft by the proper arrangement of piston rod, cross head and connecting rod, the cross head has real guides to take up any lateral forces. Everything just like the big ones!
- The steam distribution to the cylinders is of course regulated by separate valves. These are now flat slide- or D-valves and work within the steam chests fitted to each cylinder. The steam pressure pushes them against the equally flat valve faces of the cylinders. Slots are milled in to these faces to time and distribute the steam.
- This type of valves is very wear resistant because here flat works again flat, in fact they are known to actually improve their fit with running in.
- You need two servos to control this type of engine:One servo is needed for the reversing gear because now reversing, i.e. controling the direction the engine is running, is done by a mechanical system.There are dozens of different valve gears, for our model CRISTAL we chose to use the “Stephenson” system.
- The second servo is linked to the separate steam regulating valve and controls the speed of the engine from “stop” to “full power”.
- Very near scale appearance, with their great number of moving parts it is very enjoyable to watch these models running.
- Function and behaviour correspond very closely to the original engines.
- Despite the larger number of moving parts these engine are rather wear resistant, with adequate care these engines will last a long time.
- Well built and maintained engines can run practically drip-free because all piston and valve rods are sealed with stuffing glands which can be re-tightened if required.
- A good slide valve engine can be more efficient then the other types.
- You need two servos to control a slide valve engine by radio control.
- More oil points, everything that moves must be oiled.
- A little bit more maintenance work: For a model steam engine to retain it’s value and performance it is recommended to clean and maintain it regularly.
But this, in fact, goes for all steam engines!
If you wish to enjoy such a beauty-full engine for a long time:
- Engines with mechanical reversing gear should not be reversed “flying” while running!
Always close the steam valve first and stop the engine, then reverse and then open the steam valve again. A good engine will have no trouble to restart!