How to use a model steam engine Model steam engines can be used to demonstrate a complete energy conversion system and to show good health and safety practice. They are very safe, if the guidance below is followed. This information complements that in the CLEAPSS Laboratory Handbook, section 9.7 and in guide L214 Examining Autoclaves, Pressure Cookers and Model Steam Engines. Under the Pressure Systems Safety Regulations, a regular inspection is required using a simple written scheme, as provided in guide L214. A technician could carry this out, unless an employer decides otherwise. Steam engines should only be used by science department staff that have received appropriate instruction (eg, they are familiar with this leaflet). The simplest stationary steam engines are best for teaching. These (and spare parts) are available from science education suppliers. This leaflet shows the popular Mamod model SP4 (www.mamod.co.uk). A similar engine is the Wilesco model D6 (www.wilesco.de). A small electric generator (often a dc motor working as a generator) is also shown. This can produce enough electricity to operate a voltmeter, light emitting diodes or a small filament lamp. Safety checks • Always carry out checks 1 to 5 below, before using a model steam engine. • If the engine is unusual or very old, check with CLEAPSS before use1. 1. Ensure that the steam engine will not vibrate across the bench when it is running. Fixing the engine to a plywood baseboard is recommended. A G-clamp could be used to secure the unit to the bench. 2. Check the whole engine for signs of corrosion or damage. 3. Unscrew the safety valve. Check for free movement of the sprung pressure release mechanism and any sign of corrosion or damage. 4. Check the condition of all sealing washers and O-rings, usually on the safety valve and the whistle. Replace washers or O-rings if damage is suspected. 5. Check that no bolts or screws are loose, particularly the pivot bolt which holds the cylinder and piston assembly against the faceplate. 1 For example, engines made many years ago by Stuart Turner and supplied by MLI may be unsafe. PS80 JRE 09/08 © CLEAPSS®, The Gardiner Building, Brunel Science Park, Kingston Lane, Uxbridge UB8 3PQ Page 1 of 3 Tel: 01895 251496; Fax: 01895 814372; E-mail: [email protected]; Web site: www.cleapss.org.uk Lubrication 6. Put a drop of clean car engine oil on moving parts and bearings of the piston and drive mechanism. Use a suitable dispenser and avoid skin contact with the oil (See CLEAPSS Hazcard 45B). Filling the boiler with water 7. Open two holes in the boiler, normally by removing both the safety valve and the whistle. 8. Place a small funnel in one hole. Add just- boiled distilled water from a kettle through one hole; air should be displaced from the other hole. 9. Fill the boiler until water reaches the top level marker on the sight glass. 10. Replace the safety valve, whistle and any other plugs in the boiler, ensuring that they are finger- tight only. 11. If the cylinder is fitted with a control valve, set it to the closed position (usually upright). Fuelling and starting the engine • Never use a methylated spirit as a fuel. Always use solid fuel tablets, specifically supplied for model steam engines, in a proper solid fuel tray with a handle. • Fuel tablets usually contain hexamine (methenamine) See CLEAPSS Hazcard 3B. They should be stored as flammable solids [FS] in dry conditions and not used if they have ever been damp. • Unless they are wax coated, avoid touching the tablets or wear nitrile gloves. • When any burning tablets are not under the boiler, wear safety spectacles, as some have been known to spit. • Operate the engine in a well-ventilated area, eg an open laboratory. • Take care, because the engine and steam it produces will be extremely hot. • Consider the use of a safety screen if observers are likely to get close to the engine. PS80 JRE 09/08 © CLEAPSS®, The Gardiner Building, Brunel Science Park, Kingston Lane, Uxbridge UB8 3PQ Page 2 of 3 Tel: 01895 251496; Fax: 01895 814372; E-mail: [email protected]; Web site: www.cleapss.org.uk 12. Place the fuel tray on a heat-proof mat. Add no more than two tablets side by side. 13. Wear safety spectacles. Lighting the tablets with a splint is usually easier than with matches. Hold the tray handle and slide the flaming fuel tray under the boiler, ensuring that it locates properly. Remove safety spectacles. 14. If hot water has been used, it should re-boil in a couple of minutes. 15. Use pliers to lift the hot safety valve carefully and ensure that steam escapes easily. (If the valve does not release steam, wear safety spectacles, remove the flaming fuel tray, put it on the heat- proof mat and carefully place another heat-proof mat on top to extinguish the flames – this may take a minute or two). 16. Test the whistle, using pliers to operate the lever, in case steam is ejected towards the hand. 17. If the cylinder has a control lever, move it to allow steam into the cylinder. 18. Spin the flywheel and the engine should start. 19. Some control levers have 3 positions to allow the engine to be stopped or reversed. 20. When the fuel tablets are used up, the engine will stop. This should be well before the boiler runs out of water. Always refill the boiler with water if the level goes below the bottom of the sight glass or before using new fuel tablets. Never refill the boiler whilst fuel is still burning. Running the boiler dry can be dangerous and may damage the engine beyond repair. Shutting down 21. Whenever possible, leave tablets to burn out in the tray under the boiler. This is safest and avoids disposal problems. 22. Allow the engine to cool. Remove the safety valve and whistle from the boiler, invert the engine over a sink and allow remaining water to drain away. Always ensure that the engine dries out fully. Take care to keep the safety valve and whistle securely but remove them from the boiler to maintain ventilation and to ensure that the boiler remains dry during storage. PS80 JRE 09/08 © CLEAPSS®, The Gardiner Building, Brunel Science Park, Kingston Lane, Uxbridge UB8 3PQ Page 3 of 3 Tel: 01895 251496; Fax: 01895 814372; E-mail: [email protected]; Web site: www.cleapss.org.uk.