The term live steam refers to small models of leisure or study, driven by a steam engine .
These are mostly model steam locomotives , steamboats or locomobiles .
The operation of a model steam engine is close to that of a real machine. The mechanical components are sometimes over-sized compared to the scale of the model , to allow a better operation, a better maintenance, a better use. For a small model, the simplicity of manufacturing the components takes performance. As models to start, single-cylinder machines that require assistance to start.
Steam is produced from water and a heat source that can vary depending on the scale chosen. In the case of small scales 1 , liquids ( alcohol , ethanol, etc.), butane , or electricity ( heating resistor which directly heats the water) are used as fuel . For larger scales, fuels used on real models such as coal , diesel , gasoline or propane gas are used .
There are many orders for live steam engines:
- On the job : the machine is controlled directly by the driver. This type of control is possible on a fixed machine, or on a mobile machine that the driver can follow (on foot, sitting on it, reduced radius of action …).
- Remote : The machine is remote controlled, because of its mobility and size too small to ship the driver.
- By remote control , where a system of servomotors actuates the various controls of the machine.
- By the command transmitted via a wire, or by the way in the case of trains.
Steam was born with the steam locomotive . The first models made were study models for workshops and schools of fitters [ ref. desired] .
In France, from 1880 to 1930 , the house Radiguet and Massiot produces live steam toys 2 . In the 1950s , there are JC brand steam engines (Jean Comby) marketed with NOVA 2 steamers .
Before the appearance of the internal combustion engine , there are some achievements of steam airplanes 3 .
There were railways from 1894 in public gardens in the United States (Cagney) and 1904 (Miniature Railways Ltd) in England to entertain the public 4 . In 1927, the Romney Hythe and Dymchurch 5 , the railway network in 15 “( 381 mm ) gauge is based. It is located south of England in Kent near Dover and still operates today. Walt Disney built the Carolwood Pacific Railroad in 1950.
In the model ship at the end of 1930 , it should be noted the influence of Gem Suzor (President of the Model Yacht Club of Paris), which carried steamboats to flash 6 .
There are many suppliers of plans, foundries and models in Europe, and some craftsmen in France.
In England , there is one of the oldest journals on the subject, founded in 1898 , Model Engineer magazine . In France , specialized magazines on live steam are created in the 1970s , Mechanics and Models, Mini Engineer Vaporist and in 1977 the magazine Escarbille published by the Brotherhood of Amateurs of Steam 7 .
There is also information on beautiful achievements in specialized journals on naval modeling.
The majority use of live steam is made for the outdoors. The materials are mostly manufactured by their owners, although there is industrial production for smaller scales, naval modelingand technical toys (brands Wilesco, mamod …).
For the fast steam yard train , the notation of the ladders is traditionally in Anglo-Saxon measurements , because of the origin of the practice of the live steam: one counts the number of inches to the scale per real foot . The most common scales are: I (1:32) 8 , II (1: 22,5) 8 , 1/2 “ (1:24), 3/4″ (1:16), 1 “ (1: 12), 1-1 / 2 “ (1: 8), 2-1 / 2″ (~ 1: 5) and 3 “ (1: 4). From 3/4 “(1:16), the models are bulky and powerful enough to tow a large mass, starting with the driver.
The main spacings encountered are: 32 mm, 45 mm, 89 mm (becomes rare), 127 mm, and 184 mm [ ref. desired] . The actual scale of reduction is obtained by dividing the gauge of the railsof the real model reproduced by the spacing of the model in reduction. For reasons of equipment compatibility and reduced model networks, the gauge is standardized 9 , 10 .
There are, however, small scale models of trains at scale 0 (1:48 in the United States ), or at scale 00 11 (1:76 in Britain ), but they are still rare.
The types of steam generators (boilers) are mainly of the “smoke tube” type (see Boiler The motors used are of all types, with single or double expansion for the most complex ones.
For shipbuilding , the fuel used is usually propane or butane gas . The advanced models are equipped with an automatic burner controller depending on the boiler pressure as well as a servo- controlled ( Bypass ) water supply circuit and remotely.
The types of steam generators (boilers) are of the smoke tube type, water and flash.
The simplest model, which is also a toy, is nicknamed the POP POP .
The engines used are of all types, single, double or triple expansion or steam turbines.
Note that before the 1940s , before the appearance of powerful enough internal combustion engines , there were competitions of steamboats 12
Agricultural and Road Machinery
They are faithful reproductions or not of machines used on farms ( locomobile ), construction sites, carnivals, etc. before the appearance of the combustion engine.
There are also reproductions of steam trucks and automobiles .
The types of boilers are mainly smoke tube type [ ref. desired] .
Types of machines
The steam generator
On the simplest models, the overall efficiency is not a concern, it produces only saturated steam without overheating . The boilers are very simple and usually only have a firebox , without return tubes or economizer.
On more complex models, boilers are smoke tube type (railway use) or water tube (marine use), there are also instant spray generators, almost abandoned system nowadays because difficult to develop, despite its weight / power advantage (marine or aeronautical use) [ ref. desired] .
The most advanced models (compound locomotives) are equipped with superheating tubes immersed in the combustion gases, or directly in the furnace, the temperature of the steam being higher, a so-called overheating oil (of grade SAE 800- 1000) must be used for engine lubrication.
The steam generator ( boiler ) must include the following safety devices:
- a water level to control the amount of water in the generator.
- a safety valve to limit the pressure in the generator.
- incidentally a manometer .
The steam generator is sized to deliver a sufficient steam flow to the engine power and other equipment, it allows for easy cleaning if possible. The vaporisation of the water imposes minimum dimensions of the generators (cf studies of Clément Ader on the miniaturization of the steam generators [ ref. ] ) So that the water can remain in contact with the plates of the generator without being replaced by the steam ( harmful cavitation effect). It is for these reasons that the dimensions of the model are not exactly identical to the model reproduced.
For instantaneous vaporization , the same principle as the Serpollet generator is used, regulation is done by the introduction of water.
- Single cylinder machines
- These machines may require assistance to start if the piston is on one of its dead spots. Single-cylinder machines can generally operate in both directions without a particular device, simply pushing them in the desired direction.
- Two-cylinder machines
- Single-expansion twin-cylinder machines have 90 ° staggered linkages to allow starting in all positions. Twin compound (double expansion) machines are generally used for marine applications. There are tri-compound engine reproductions (triple expansion).
- Machines with oscillating cylinder (s)
- The entire piston / cylinder is mounted to pivot and functions as a system connecting rod of variable length. The rotation of the cylinder relative to its support plate ensures the distribution of the steam by opening or closing lights . This system is the simplest that exists for steam engines, but is not representative of full-scale models. It is sometimes used in machines where the cylinders are hidden, as produced for example by the German company Regner in its Easy line series .
Rare in the world of modeling, they are quite simple design, single-stage, the number of nozzles feeding the turbine is variable.
The distribution of steam
In particular, in order to improve the operation at the various speeds and to ensure an easy inversion of operation, complex rod distribution systems have been developed for size machines, the most used being the Walschaerts Distribution . There is also sometimes a Stephenson type distribution . These systems being complex, on the basic models one often finds simple distributions said to eccentric . In this case, the reverse direction, if it exists, is made by reversing the steam distribution using a four-way valve .
Used mainly on boat models, it allows to recover water to increase the autonomy. A good condenser also allows to gain power by creating a vacuum at the output of the engine (gain in pressure).
On [Qui?] Has long used liquid fuels, mainly denatured alcohol that was simply burned under the boiler, which then does not have a combustion chamber or fireplace. As a result of various accidents (tank overturning), this system has sometimes been replaced by capsules containing a gelled fuel (solidified alcohol, solid barbecue type ). The use of gasoline is now completely abandoned, its use carries the risk of explosion and fire in case of rollover.
Currently, the vast majority of small models run on gas with a burner under the boiler , or preferably in a firebox similar to that of full-size boilers. Gas operation is considered safer and simpler [ ref. desired] .
The use of coal (anthracite type) as fuel is conditioned by the use of a furnace with a sufficient surface area to obtain a homogeneous , continuous and easy-to-maintain combustion , the minimum grid area is approximately 10 cm² [ ref. desired] , below, the ignition and holding of the fire are delicate operations.
The use of wood is possible, but the calorific value being lower than coal, it requires more frequent maintenance and adaptation of the grid by replacing it with a plate with holes [ ref. desired] .
The diesel fuel requires the use of a burner for a correct combustion and if possible a vault made of refractory materials in order to absorb the thermal shocks quite harmful to the life of the steam generator [ ref. desired] .
- For small models
The management of a pump for filling the boiler from a water tank is complex, the vast majority of models consumes only water available in the boiler after which it must depressurize it to fill it again.
- For larger models [evasive]
The water is introduced into the boiler by the use of a mechanical pump (hand pump, driven by the motor …), a feed pump (also called “small horse” [ desired ref. ] ) or a Giffard injector . These models have sufficient autonomy to operate for several hours by collecting the feed water in tanks. The control of the feed equipment is done manually or by model- making servomotors .
Combustion in the absence of water or a lack of water presents the same dangers as for a full-size boiler: it may explode [ ref. desired] , which can lead to serious burns if nearby.
On small models, in order to limit the risk with gas or solid fuel boilers, the fuel or gas is usually exhausted before the water. The use of a steam generator therefore requires permanent monitoring.
The boiler is equipped with a water level which makes it possible to check the quantity of water remaining in the boiler. The level is then a security organ.
The water used must be distilled so as not to have dissolved solids that are deposited entirely in the boiler during the formation of steam, thus generating a grime that lowers the efficiency of the machine. Deionized water is very aggressive for metals must be cut with 2 to 3% tap water [ ref. desired] .
A steam engine requires a continuous supply of lubricant in the cylinders, which is generally provided by a mechanical pump or a condensing lubricator (also called displacement).
On the important models a SAE 300 grade motor oil is used; on the small models of olive oil is usable. Note that the use of automotive engine oil is not advisable, because of its emulsion with water and the risk of inhalation of additives [ ref. desired] .
The lubrication of mechanical parts such as distribution and connecting rods is ensured by various systems with mechanical oil .
The heating is generally constant and regulated by modulating the gas valve. When there is too much steam, the pressure rises until it escapes through the valve , safety organ. There are gas regulators depending on the pressure of the boiler.
- With a solid fuel (solidified alcohol type)
The heating is generally not adjustable, the amount of fuel is generally adapted to the boiler by the manufacturer.
There are several factors to manage, among the main draw is the most important.
The draft, the suction effect of the combustion gases in the smoke tubes, is generated by the engine exhaust gases in the chimney. When stopped, the blower, a jet of steam, is used to replace the exhaust and maintain the fire in the home.
If the boiler is equipped with an ash pan (or “ash box”) equipped with control flaps, it is possible to influence the fire resistance and the combustion of the coal. The quality of the coal and its distribution have an influence on the behavior of the fire. Some rail models, usually large machines (250 – 300 kg ) are equipped with an adjustable exhaust to balance, in operation, the draw depending on the towed load. In some cases they are removable nozzles at the exhaust outlet.
Regulation of engine speed
Speed regulates in two ways:
- Either opening more or less the steam distribution valve, called regulator;
- Either by mechanically controlling the distribution if it is adjustable, which allows a rapid response of the system.
The action on the distribution acts on the relaxation of the steam.
The reversal of change
- For the simplest systems, it can be done by pushing the locomotive in the sense that we want to see it go.
- Inverse flow can be provided by reversing the flow of steam using a four-way valve ;
- One can have a mechanical reversal reversing the cylindrical or plane drawer opening control , by a system of levers, Walschaerts type or other.
The order type
The locomotives can be manually operated and in this case they run continuously until they stop or they run out of fuel, or be radio controlled. According to the type of distribution, the radio control is done with a single servomotor for the speed and the reversal of operation, either with two separate servomotors.
Schematic diagram of a locomotive with simple distribution
- In the context of a steam engine , the term live steam refers to steam produced under pressure, not yet used to produce a mechanical force. The steam used is the expanded steam , and is intended to be reused in a low-pressure cylinder or to be evacuated by the exhaust (chimney).
- In the context of an evaporator , live steam refers to the heat source used to achieve the heat exchange necessary to achieve the concentration of a product.
Notes and references
- ↑ Until 1: 22.5 for trains.
- ↑ a and b SAKER Steam-Publishing Machines, page 94
- ↑ ( in ) FLYING STEAM ENGINES [ archive ] , on the site flysteam.co.uk
- ↑ historical references 7 “1/4 Gauge society Ltd [ archive ]
- ↑ “Romney Hythe and Dymchurch” [ archive ]
- ↑ Steam boats with flash [ archive ]
- ↑ http://www.cav-escarbille.com/index.htm [ archive ] </ Brotherhood of Steam Amateurs
- ↑ a and b Normalized by MOROP and NMRA
- ↑ 7 “1/4 gauge society [ archive ]
- ↑ Information available from the Brotherhood of Steam Amateurs [ archive ]
- ↑ Presentation on the site of the manufacturer Hornby [ archive ] Mallard locomotive at scale 00 (1:76) running on live steam.
- ↑ ( in ) ” Tethered Hydroplanes. From 5 mph. to 135 mph. in a Century. ” [ Archive ] (accessed on 1 st August 2009 )