4. General Operation Of a Steam Plant



This note is intended to address the interests of new users of Miniature Steam” oscillating steam engines. Since an engine alone has no purpose but to look beautiful, its operation must be seen in the context of the components that are required for it to perform its primary function of powering something – in this case we are highlighting the operation of an engine in an integrated steam plant using Miniature Steam” 3” horizontal boiler and Clyde twin cylinder oscillating engine built to power a radio controlled boat. The descriptions apply generally to any engine/boiler combination.


The engine must be mounted on a firm base – a brass mounting tray is used in the illustration. Beware of mounting the engine on an uneven surface. This could lead to distortion of the engine base when screwed down. In turn this could cause binding of the crankshaft in its bearings leading to poor engine performance if not actual seizing of the engine.

The engine is connected to the boiler by a steam pipe with steam cocks usually at the engine end with oscillating engines. Steam passes through the boiler steam cock and through the lubricator, before entering the engine under control of the engine control valve (not identified). The engine control valve controls the direction of rotation of the engine as well as the power required from the engine. It directs live steam into the engine and spent steam to the oil trap. The oil trap separates the oil from the exhaust steam and clean steam is passed to the exhaust port (not shown). The boiler burner is powered, through the gas pipe from a refillable gas tank. The tank is fitted in a way that enables easy removal from the tray for refilling which should be done in open air – not with the tank in a confined space. Steam pressure is indicated on a pressure gauge and a safety valve can be adjusted to release steam if the pressure exceeds a safe level for the specific boiler. Water level in the boiler is indicated by a sight glass fitted to the end of the boiler.

NOTE: Using compressed air to run the engine:

We have recently revised our policy on the use of compressed air.

The internal parts of a steam engine need lubricating more than many of the external parts. An automatic compressed air lubricator, functionally similar to our steam displacement lubricators, is a complicated and expensive device that would put our engines out of the market. It is possible to intermittently inject oil into the engine input channels and successfully operate an engine on compressed air for a long time IF the injection is of an appropriate oil, injected at the right frequency and right quantity to ensure proper lubrication. Even if these three factors can be quantified reasonably, there remains the question of where to inject it in the engine. A "T" piece with an on/off cock in the input steam line is the most obvious answer, or where a plastic pipe is being used for the steam supply - just pulling it off and injecting the measured quantity of oil directly into the steam entry to the engine can work.

Unfortunately, in the past a number of our customers have not understood anything about the lubrication needs of an engine and have made warranty claims for engine failure that was obviously caused by running the engine without any oiling - internal and/or external!

In the publication of this explanation we are revising our "NEVER" use compressed air to "BE CAREFUL" to properly lubricate your engine if it is running on compressed air along the lines suggested above. The damage that an engine that has not been properly lubricated is obvious - and that is what will void a warranty claim.


Fundamental to operating a boiler is a heating device. Some of the smaller boilers use spirit or tablet heat sources but the more powerful boilers are generally heated by various gas types delivered through ceramic burner elements. Generally, there are two types of ceramic burner elements – those that are machined out of general purpose heating tile blocks and those that are constructed as cast ceramic elements tailored for the burner/boiler combination. Miniature Steam” boilers exclusively use the custom designed cast ceramic elements because of the superior heating performance that may be obtained. To obtain this maximum performance, these burners need to be tuned to the actual installation. Appendix 1 following provides instructions for calibrating these burners.

Boiler Water Level:
It is important to ensure the correct water levels are maintained in the boiler by proper use of the water level sight glass. This is fitted to the boiler so that it shows water levels in a safe range. If the water level is not showing, the boiler has too much or too little water. Too little water can result in boiler damage. Too much water will impede the generation of steam and result in poor boiler performance and excessive water in the steam line. Boiler feed pumps, mechanically connected to the engine, steam driven and manually operated, can be used to maintain water levels during a run, but a well-designed system will have balanced gas supply vs. boiler water capacity that will give session running times of 10 to 30 minutes. Miniature Steam”  3” horizontal boilers are refilled by removing the safety valve. The 2”, 3” vertical and 4” boilers have separate filler nuts for water refills. With 3” & "Econo" vertical boilers this is located under the cowl and with the 3” & 4” horizontal boilers it is adjacent to the safety valve.

The Pressure Release Valve (Safety Valve) For more information see Library Guide 12.


Each boiler is fitted with a pressure release valve that will vent the steam from the boiler if it passes a pressure appropriate to each boiler. This pressure is NOT set at the factory on delivery; the customer must make a setting according to local conditions and regulations. The 2” boilers, 3” vertical boiler and 4” horizontal boilers have a valve that can be adjusted without removing it from the boiler. The valves on the 3” horizontal boilers must be removed to adjust the release pressure. During commissioning, on each run allow the valve to discharge and note the discharge pressure before drawing off steam. At the end of each run, when the boiler is cool, adjust the valve as follows:

For 2” boilers, the 3” vertical & 4” horizontal boilers, slack off the lock nut at the top of the valve and rotate the valve setting nut (the component with 4 holes in it); clockwise to increase the release pressure anti-clockwise to reduce the release pressure, a quarter turn at a time. Re-tighten the lock nut before starting the next run. For 3” horizontal boilers remove the valve, slack off the lock nut (the one on the end of the assembly) and vary the setting of the adjusting nut, a quarter turn at a time; clockwise to increase the release pressure, anti-clockwise to reduce the release pressure. Re-tighten the lock nut and replace the valve in the boiler.
Repeat the procedure until the valve starts discharging at the required pressure.

Coping with condensate:
In simple terms steam is water vapour that is produced when water is boiled. It will return to water if its temperature is reduced below the boiling point of water. When delivering steam from a boiler to an engine, the higher the delivery temperature and pressure the more power can be generated by the engine. Thus, heat lost by the steam after leaving the boiler and arriving on the top of an engine piston will reduce the potential power of the engine. In the extreme case of steam being delivered to a cold engine the steam will condense to water in the engine cylinder and impede its operation.
With oscillating engines this results in water/steam bubbling between the cylinder and trunk during warm-up.
Slide valve engines have manually operated steam cocks to release condensate when it becomes a problem at start-up. In most locations the engine is able to discharge condensate automatically – perhaps with a little finger nudge to the flywheel

Steam Oil Separator:
At the other end of the steam journey, to meet environmental requirements, the spent steam, with the lubricating oil drawn in from the displacement lubricator, has to be passed through a steam condenser/separator, sometimes called an oil trap or steam trap. In this component the lubricating oil in the steam is separated from the cooled steam and the clean steam proceeds to the atmosphere minus its oil load. The oil collected is extracted from the condenser, and discarded, at the end of each run using the syringe supplied. Do not be tempted to re-use the collected oil. Always use the syringe to take out the oil in the condenser while it is still warm. It can be difficult to draw out if it is allowed to cool before extraction. Do not use the extraction syringe for loading clean water into the boiler. We supply a second syringe for this purpose.

Boiler Lagging:
Historically most working boilers were clad with insulating materials to minimise heat loss from the boiler shell. “Miniature Steam” 3” & 4” model boilers are supplied with a wood lagging kit for self-assembly to help minimize heat loss. There are a number of factors to consider before deciding to install lagging on your boiler (See Appendix 2 following for installation guidelines). An additional benefit of the wood lagging is to improve the cosmetic appearance of the boiler and to minimise risk of contact skin burns during operation. If wood lagging is not desired for a particular situation, e.g. cold ambient temperatures requiring warming of the gas tank for efficient combustion, the highly efficient Miniature Steam” cast ceramic burners generally provide sufficient heating capacity to cope with radiant heat losses from an unlagged boiler in reasonable ambient temperatures

Why/how to lag the steam supply pipes:
In normal industrial situations the distance between a boiler and the engine generally was sufficient to require lagging of the steam supply line to minimise heat loss. This was a commercial imperative that does not necessarily apply to modelling situations when the original design is scaled down. It may be advisable where the steam line is relatively long, or when there are many stop/start actions that will leave live steam in the pipe long enough to lose significant heat when manoeuvring the boat. Otherwise it only needs to be used to authenticate the model. This can be accomplished by closely wrapping fibrous string (cotton- not synthetic fibres) around the steam line and painting with a suitable white paint

: (see Coping with condensate above). During warm-up oscillating engines eliminate condensed steam and lubricator oil by “blubbering” between the cylinder and the trunk during warm-up. This is the process that happens as steam is being delivered to the engine while the engine is at a temperature that will condense the steam to water. As soon as the blubbering stops the engine will operate normally. This is also a safety feature of oscillating engines in that steam pressure beyond the design limit will cause the cylinder to lift off the trunk and relieve excess pressure. With oscillators if you experience prolonged blubbering at warm-up or during post warm-up activity this will indicate some serious overload on the engine that should be corrected before continuing.

The role of the lubricator: (For more information see Library Guide 20, Library Guide 22, Library Guide 23 & Library Guide 24
It is imperative that the cylinder and other internal moving parts are lubricated to minimise wear on the engine. When powering an engine with steam a special high temperature lubricant called “Steam Oil” should be used. This is dispensed by a “displacement lubricator” that injects the oil into the steam supply line while the engine is operating. It works by condensing small amounts of steam in the lubricator body. After the steam condenses in the lubricator, the oil floats on the top of the water and overflows into the delivery pipe where it is atomised and carried to the valves and cylinders. After each run the displacement lubricator should be drained of water and topped up with oil.
As noted above a displacement lubricator is not appropriate where the engine is powered with compressed air.(See note starting on the first page of this document)

General lubrication after each run:
Light machine oil is recommended for all mechanical parts outside the steam system. Some engines have oil cups to lubricate specific components but these do not cover all surfaces. For working surfaces that do not have an oil cup, squirt the oil in while turning the engine over by hand.

General housekeeping:
It is normal for steam plants to get “messy” during operation. The steam plant tray has fold up edges to collect water and oil to minimise the “messiness” extending to the rest of the installation. It is good practice to mop out the tray after each run and generally wipe away any splashes on the components.

Long term storage:
Generally an engine’s cast components are made from a marine grade non-corrosive alloy; the crank- shaft is made from stainless steel (oscillators SG Cast iron for slide valve engines) and the remainder of the machined components from brass. This combination provides maximum protection from corrosion during service if the engine is run regularly. However if you are planning to not run it for a prolonged period – say 3 months or more, the condensate that will remain in the cylinder after a run may cause some tarnishing of the cylinder bore. This could cause accelerated wear of the “O” rings and increase the internal friction of the engine during initial startup. In these circumstances we recommend that you remove the top and bottom cylinder covers, soak up the condensate, directly lubricate the cylinder bore (preferably with benign rubber grease) and replace the cylinder covers before storing the engine. This advice does not apply to the Avon engine where the cylinder is factory assembled and should not be dis mantled

 Boiler Size vs. Power Requirements:
There is a direct relationship between the required size of boiler and size of engine for the current range of Miniature Steam” products. The following table illustrates the options available:









Twin cylinder 8 mm bore/ 11 mm stroke





Single cylinder 11 mm bore/ stroke





Twin cylinder 11 mm bore/ stroke





Single cylinder 19 mm bore/ stroke





Single cylinder 19 mm bore/ stroke





Twin cylinder 19 mm bore/ stroke





Twin cylinder 19 mm bore/ stroke




Twin Avon





Twin Tyne





Twin Clyde






If a plant is being configured with other third party components the above sizing can be used as a guideline but please note that Miniature Steam” boilers have superior steam generating efficiency when compared with most other boilers of similar size. Also, when sizing a boiler it may be important to anticipate the use of steam driven accessories such as steam driven boiler feed pumps. There should be no problem with using a larger boiler than the above recommendations to cover this situation

Appendix 1.

The burner converts liquid gas into heat by burning a gas and air mixture in the burner assembly to create heat. “Miniature Steam” burners use individually designed ceramic burner inserts to provide maximum burner efficiency for each boiler. Following is the description of how to calibrate a burner for maximum performance

Calibrating “Miniature Steam” Ceramic Burners

Please note that “Miniature Steam” ceramic burners are only to be used with a Butane/Propane gas mix with a maximum of 30% Propane or Butane/ISO Butane/Propane mix.

LPG (100% propane) should NOT be used.

“Miniature Steam” ceramic burners are specifically designed to provide optimum burning characteristics in enclosed spaces such as the centre flue or firebox of a boiler. They differ from other ceramic burners made from heating tiles designed for radiant room heaters.
The gas/air mixture of a “Miniature Steam” ceramic burner burns outside the ceramic insert (see picture). This results in a more efficient transfer of heat to the boiler’s heating surface. The burner also remains relatively cool thus improving the thermal efficiency of the burner and minimizing the chance of back burning.
Please note that when the burner “roars” it is probably operating efficiently. 2” and 3” boilers have a steady sound where the 4” boiler has a “stuttering” sound imposed over the top of the roar. These sounds are normal for “Miniature Steam” burners.

As the gas supply may vary by location and from batch to batch, it is advisable to undertake a calibration process before starting up a boiler for the first time and when changing gas batches.

To achieve the correct burning characteristics of the unit with any gas batch, the jet holder is moved in the air/gas mixing tube to establish a correct air/gas ratio in the fire tube.
We recommend the following procedure:

      • connect the gas source to the burner gas pipe and insert the jet holder into the mixer gas tube
      • remove the burner assembly from the boiler and hold it in one hand by the mixer gas tube. (Note: keep your fingers away from the burner shroud – it may heat uncomfortably during the calibration process!)
      • start by sliding the jet holder in the mixer gas tube to leave the air holes 2/3 open. Turn on the gas and light the burner. You should see a lazy flame flecked with yellow. If not, adjust the jet holder to achieve this. This position indicates that insufficient air is being added to the gas/air
      • slide the jet holder to expose more of the air holes until the flame is blue but is ”dancing” on the surface of the burner. This indicates that there is too much air in the gas/air mix
      • move the jet holder back to reduce the air hole exposure until a stable blue flame is evident. This is the optimum setting for the air/gas mixture.
      • secure the jet holder in the mixer gas tube in this position with the Allen key supplied by tightening the stainless steel 3 mm grub screw provided.
      • turn the gas off and allow the burner to cool a little before reinserting it in the boiler fire tube

When in place in the burner tube the burner is normally lit by turning on the gas and applying a gas lighter as illustrated to the boiler chimney. These are generally available in normal supermarkets. Another alternative is to place the tip of the lighter under an air hole in the cowl,light the lighter and turn on the gas.

The Gas Supply.
The gas used in the burner is supplied as a compressed liquid that follows the immutable laws of physics. Simplified for this note, these mean that when liquid gas in the master reservoir is transferred to a storage container the storage container will get colder, as will the master reservoir. When the gas is drawn off in gaseous form during use, the storage container will again get colder. These facts require particular attention.
“Miniature Steam” steam plants have the refillable gas tank attached to the gas delivery line with a knurled nut fitting and the tank is not physically secured to the mounting tray. This is to enable easy detachment for refilling in open air.
Depending on the ambient temperature at the time and the rate of filling, the tank will cool and may even frost up. If this happens, the tank should be brought back to room temperature by dunking it in warm water before refitting it to the plant.

In normal circumstances the above step should be sufficient to get optimum gas release in starting the operation of the plant but there is still the possibility of chilling from rapid gas expansion during early use. This will reduce the amount of gas available for heating and affect the performance of the plant. “Miniature Steam” plants locate the gas tank as close as practical to the boiler (preferably unlagged) so that there is progressive warming of the gas tank as operation proceeds. In extreme ambient conditions it may be necessary to divert the steam exhaust line through a coil wrapped around the gas tank, to provide the additional warming to offset the cooling process

Library Guide 10. Gas for Model Steam Boilers provides much more information on this very important subject. 

Appendix 2

The lagging items supplied with “Miniature Steam” 3” & 4” boilers comprise suitable sized strips of wood and brass bands to hold them together for an authentic presentation. If a lagged boiler presentation is desired either of the following procedures may be helpful.

Option 1:

      • Lay out the slats on a flat surface to form a mat and check for any size variations.
      • select one slat and fit it to the part of the boiler with the most fittings. Using a sharp knife shape the slat so that the edge fits to the centreline of the fitting/s.
      • place two rubber bands on the boiler to hold the slat in position. Position the rubber bands where the brass bands will be
      • repeat this procedure to position each slat around the
      • gently sand the lagging to remove the ridges that occur where the slats meet and give the lagging several coats of acrylic varnish to seal the
      • when the varnish is dry, fit the boiler bands to secure the lagging and remove the rubber

Option 2:

      • starting at the top centre of the boiler cut the wood planks to fit between the castings etc.
      • glue the wood cut outs in place using super glue. (Cyanoacrylate, or CA, medium viscosity)
      • continue gluing the planks in place and cut out were necessary.Pay extra attention to getting the first planks parallel to the Centre line if the boiler
      • after you have finished sand the planks to a smooth finish. Leave the dust remaining in the cracks between the planks
      • paint the planks with a satin or semi-gloss varnish. Make sure it is dry before heating the boiler!
      • place the brass bands around the finished planks and bend up the ends, leaving a 1/8" gap between the two bent-up ends. Gap is important!
      • Drill holes in the bent up ends and secure in place with the screws and their nuts
        Note: the CA glue may fail after the boiler heats and cools several times, but the brass banding should capture all the pieces and hold them in place. The bands have to be tight, and this is why the gap between the bent ends is so necessary before the screws are tightened.