All About Engines

292 All About Engines Five per cent, of this will be 144,000 lb., or more than 64 tons, and for a voyage of only ten days’ duration more than 640 tons of fresh water would Vertical section Horizontal section Figs. 168,169.—Weir’s Lunette evaporator have to be carried to supply the boilers alone, to say no- thing of the requirements of the passengers. It follows, therefore, that every ship must carry evapor- ators by means of which fresh water can be prepared from sea water. An evaporator is really a boiler, charged with sea water, which is heated by means of coiled pipes supplied with steam. Horizontal and vertical sections of one of Weir’s Lunette type evapora- tors are given in Figs. 168 and 169. It will be seen that there are a number of copper coils placed one above an- other in the lower part of the evaporator, which has a door in the side so that they can easily be removed and cleaned. The steam is usually taken from the main boilers. The older plan was to take it from the intermediate cylinder valve chest, but the higher temperature of the steam in the boilers enables smaller evaporators