Stoking the steam, one engine at a time…
Steam Boat Modellor
Stuart Turner logo
  • © 2018 Steve Allen Contact Me 0

Compound LaunchCompounded Conservation

Type: Vertical, Compound, twin cylinder, double acting, slide valve.
Bore 3/4-in. and 1 1/4-in.
Stroke: 7/8 in
Height: 5 1/2 in
Weight: 3 3/4 lbs.
Availability 1924-today
Design: 5 column marine engine


3/4-in. and 1 1/4-in. Bore x 7/8-in Stroke.

Height 5 1/2-in. Overall Length 5 1/4-in. Weight 3 3/4-lbs.

Stacks Image 98

This is an extremely pretty and realistic small model and can be supplied with or without reversing gear.
The list of parts is the same as for the Twin Launch engine, except that piston rings are not supplied - cotton packing being used.
Full set of Castings and parts with complete drawings.

With Gunmetal Cylinders 25/- Post Free.

With Cast Iron Cylinders 21/- " "

Weight packed,


All Studs, Bolts, Nuts and Screws, price 7/- ; Four Cylinder Drain Cocks, 8/- ; Pair of Cylinder Lubricators, 5/- ; Reversing Gear Castings, Drawings and all Bolts and Nuts, 7/6.


Compound or simple, the eternal question, which is best. They both have pros and cons and its a matter of choosing which is most important. Twin cylinder simple, common 90 degree crankshaft engines have one big advantage, they will start at anypoint they stop at, so stopping or reversing dont cause any problems especially when using radio control. They also produce more power as both cylinders are connected to whatever steam pressure is available, even quite low pressure will run the engine. Steam consumption is quite high so a reasonably sized boiler is a definate requirement. Horizontal marine style boilers with low water volume and a high number of flue tubes are the best, however you will also need a boiler feed pump to feed the beast. One alternative is to use a flash steam boiler, see description below. The Compound engine is a whole different beast, as far as steam requirements the engine appears to be a single cylinder engine with the capacity of the High Pressure cylinder. As the engine only has steam feeding into one cylinder the engine can stop in a dead position that it will not restart from. To obviate this problem in a RC model, fit an Impulse Valve, see description of valves in the Pinnace Engine Sidebar. The exhaust from this HP cylinder is fed into a second Low pressure cylinder of higher volume. The ratio between the steam pressure size of both cylinders and the volume of the pipework between the two are factored into a very complex formulae to get the engine working correctly. I think I have the formulae in a book somewhere, it was way too complicated for me so instantly forgot it. Having run my Compound twin and the two I have repaired, I can say with some confidence that Stuart got it Pretty much right. So steam consumption is low but the trade off is that the engine will not run on low pressure steam. For the LP cylinder to produce work it requires a minimum pressure, the pressure supplied by the HP cylinder exhaust is lower than the HP steam input so this needs to be quite high. If you run both versions of the engine at 60-90PSI they should both produce about the same amount of work, but at lower pressures the Simple Launch should outperform the Compound. WHilst Simple engines start easier with drain cocks the compound really has to have drain cocks to get started as otherwise the LP cylinder will just fill with condensate and not warm up very fast. I have seen a drain cock fitted to the bottom of the LP valve chest to prevent the HP cylinder condensate even getting into the LP cylinder. (Seems a good idea to me.) The connecting pipe between the two cylinders should also be very well insulated. My recommendations for buying for a RC steam boat, go Standard launch engine for minimal hassle or Compound for the pleasure of overcoming the problems and being that much closer to a real boat engine.

Stacks Image 168
Full size pumping engine, basis for the No.1

Stacks Image 173
Stuart Turner No.1 with Stephenson's Reversing Gear.

Video Of Compound Launch


March 20th, 1924

F.B. writes :—
"I should like to state that I am more than satisfied with the Castings and machining. I am a new customer and I sincerely regret that I have not previously made the acquaintance of your firm, which might be called 'the Model Engineers' friend.'"

March, 9th, 1924

F.J. writes :-
"The Connecting Rod is the acme of perfection and the displacement lubricator leave nothing to be desired. Thanking you for your perfect workmanship."

Flash Boilers

Stacks Image 158
The flash boiler (also known as a monotube boiler), this consists of a very long water tube suspended in a housing with a large flame. Once brought up to temperate, very fast, any water introduced by high pressure pump instantly 'flashes' into steam and is raised to a higher temperatur, and pressure, by travelling through the long tube. The volume of steam requiresd is controlled by the volume of water pumped in. This does introduce a slight delay in speed control. As long as the energy required to convert the volume of water input is less than the amount of energy stored in the heated coil and provided by the burner they can produce large amounts of high pressure, high temperature, superheated steam. This type of boiler is very light to use as they have no large volume pressure vessel filled with water. Another advantage is that you can use ordinary or even dirty water which would contaminate an ordinary boiler. So you can even use the water the model is running in rather than having to carry a tank of feed water. (Just make sure the pond water is filtered. Any damage caused to a flash tube can be easily flushed out and should any damage occur, the tube is cheap to replace if not tricky to coil. One thing though, flash boilers should not be sealed at the output, they should be terminate in a switch valve that switches the steam between either the engine of the chimney. Startup is, fire the burner, open the steam control valve to chimnet, introduce water slowly, when steam appears at the chimney slowly switch the control valve to admit steam to the engine. Their should be a safety pressure valve connected between the valve and the engine just in case the engine stalls and the valve sticks in the engine position. One smart installation I saw had a boiler feed pump running off of the crankshaft to provide water when running and a small electric pump to prime the boiler to get things started. The biggest advantage of this type of boiler for the model maker is that no test certificate or insurance is required to run these in publlc (UK last time i checked, as far as I know, please check your local legal requirements and comply with them.. Legal disclaimer) The reason boilers need certificates, testing, insurance, etc… is that a boiler contains a large amount of water heated well beyond boiling point and steam under high pressure. should a significant rupture occur a very large cloud of flesh stripping steam will engulf the model and anyone nearby. See the image of the Loco. Note all of the engine infant of the firebox has disappeared except a few unpressurised tubes. The flash boiler doesn't store water under pressure only steam passing through the coiled pipe

Please Consider Making a Donation