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is opened sharply or steam demand is high. Thus, sensible locomotive management by the operators will help to prevent the occurrence. The phenomenon is particularly evident in areas of impure water, where boiled water creates a foam, or a mist of droplets, filling the space that collects steam at
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solids. Other forms of prevention include the chemical treatment of water before it enters the boiler. In the event of priming (and also when steam is admitted through cold piping or into a cold cylinder) the operators need to open the
167:("scum valves"), either continuously working while the regulator is open or operated in conjunction with the boiler feed, are fitted. Valves at water level reduce surface scum; those towards the bottom of the boiler help remove
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in which water is carried over into the steam delivery. It may be caused by impurities in the water, which foams up as it boils, or simply too high a water level. It is harmful to the valves and pistons, as
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Early designers fitted curved sheets below the steam collector pipe, but these were not successful as the whole of the steam space could contain foam. In districts where the feed water is unsuitable,
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The most frequent cause is running the locomotive with too high a level of water in the boiler and is most apparent when the
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and re-used, any oil or grease must be extracted as this form of contamination is particularly likely to give trouble.
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the top of the boiler, to be drawn down the steam collector pipe in the form of slugs of water. If boiler water is
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and for this reason is difficult to put right without reducing the water level to the extent that the
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is not compressible and if trapped may fracture the cylinder head or
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is washed away, and can be dangerous as any water collecting in the
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228:. New York: McGraw Hill Professional. p. 447.
219:. London: British Transport Commission. p. 69.
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of a boiler, as the best location to avoid priming.
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54:but its sources remain unclear because it lacks
217:Handbook for Railway Steam Locomotive Enginemen
210:. London: Venture and Co. pp. 281–282.
224:Woodruff, Everett B.; et al. (2004).
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