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Questions What is the meaning of the head light code on GWR steam trains? What is it that comes out of the chimney of a steam engine? What is the difference between a ‘Hall’ and a ‘Modified Hall’? How long are the cylinder drains left open for after departure?
Answers What is the meaning of the head light code on GWR steam trains? The codes were used to identify the types of trains to the signalmen and station staff as they approached (especially in the dark). The positioning of the lamps indicated the type of train.
For instance the "A" code (one lamp over each buffer) was express passenger and other priority trains (breakdown and so on). This web page may help explain: We tend to use codes "A", "B", "D" & "K" on the Gloucestershire Warwickshire Railway. The most famous code is of course a lamp on every bracket, which would indicate the royal train (missing from the web page list). What is it that comes out of the chimney of a steam engine? The answer is mainly steam (water vapour) but also exhaust from the coal fire that heats the water in the boiler to make the steam. When a locomotive 'chuff's' each 'chuff' is steam exhausted from one of the cylinders, by the returning piston that in turn drives the wheels. The steam escapes extremely quickly from the cylinder, expanding rapidly as it does so and exits out of a nozzle on top of a 'blast pipe' in the smokebox (the black round bit at the front of the engine, on top of which sits the chimney ), and blasts it out of the chimney. The steam immediately starts to condense in the much cooler air and is thus coloured white - the droplets of moisture then evaporate. The force of the 'blast' creates a partial vacuum in the smokebox and this draws air through the fire, at the back end of the boiler, making the coal burn brightly and very hot (well over 1 ,000 degrees at times). This causes the coal and the volatile gasses that come off the coal to combust almost completely, so that it is mainly CO2 that eventually exits the chimney, with the white steam. When there is black or brown smoke, it means that unburned material (hydrocarbons) is exiting the chimney - that usually happens when coal is being shovelled on to the fire. A skilled fireman, with proper control of air to the fire through dampers and the firehole door can do much to reduce smoke emission. During a day, a typical medium sized tender locomotive on the GWR will consume about 6,000 gallons of water and burn about 1 to 1.5 tonnes of coal. Can you explain the route availability and power classification symbols painted on the cabs of Great Western locomotives and what the 'X' refers to on some locomotives? Click here for a comprehensive answer to this question. What is the difference between a ‘Hall’ and a ‘Modified Hall’? The Modified Halls are an improved version of the original 4900 Hall class. For full details, click here to view the article in our “News Extra” section. How long are the cylinder drains left open for after departure? It depends on a lot of things, but the straightest answer is until steam isn't condensing to water in the cylinders. Non superheated engines will need longer as the steam is more saturated and condenses easier. The outside temperature obviously affects things as well, the colder the loco metalwork the more condensation. You'll normally see the loco moving around with the cocks open when it first comes off shed. Also when it first pulls out on the first train of the day. You'll often see the driver close the cocks after pulling away and then re -open them for a few seconds because he detects the engine note becoming "woolly" indicating that the cylinders have a little water in them. The driver will always park the engine with the cocks open so that any leak past the regulator cannot build up pressure and move the engine. They'll often open them for the first
couple of beats of a pull away if the engine has been standing, just to blow out any condensate that may have accumulated. Click here to visit our virtual footplate: the cylinder drain cock lever is on the cab floor to the right of the firebox. Hover the mouse over the lever and a description of the system and a photograph of a drain cock in operation will be shown. On your coal fired locomotives do you find the need to brush the tubes regulary, and do you ever sand the tubes on your steam engines? We do brush the tubes out, at every boiler washout. This is normally every 25 to 30 steamings. We do not use sand.
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