All About Engines

J42 All About Engines per pound of steam condensed, so that enormous quantities are required. Assuming that the engine takes 12 lb. of steam per horse-power per hour, the cooling water required will be 240 lb., and in an engine of 1,000 horse-power no less than 240,000 lb. or more than 100 tons of water per hour will be necessary. All kinds of pumps are used, but the centrifugal type is the most satisfactory, because it takes up little room and is capable of delivering large quantities of water in a steady, continuous flow. The Compound Engine When the best materials, the highest standard of workmanship, and the most scientific design have given us engines which run smoothly, with a mini- mum of friction, and wear well, and when all the operations of working have been rendered as far as possible automatic, the great problem which remains is the condensation of steam in the cylinder. More than a hundred and fifty years ago, when he was struggling to improve the Newcomen model, Watt realised that this was the principal source of loss; and he endeavoured to avoid it by two methods. In the first he effected condensation of the steam out- side the cylinder, and in the second he surrounded the cylinder with a steam jacket. Both these methods are employed to-day, and in order to ascertain why they are not wholly successful it is necessary to inquire rather more closely into the changes which occur in steam while it performs its work in the cylinder.